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Plane table In Surveying
 

Plane table In Surveying

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How to use a plane table.?

How to use a plane table.?

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    Plane table In Surveying Plane table In Surveying Document Transcript

    • CONTENTS<br />SUBJECTPAGEINTRODUCTION ABOUT THE PLANE TABLE1 – 6HISTORY AND THE EXPENSION OF THE PLANE TABLE AND ALIDADE 7 – 16 OBSERVATION USING THE PLANE TABLE 17 – 26 METHOD OF SURVEY : USING THE PLANE TABLE AND ALIDADE SURVEY27 – 34 STEPS TO AVOID ERROR WHILE USING THE PLANE TABLE35 – 36 CONCLUSION37APPENDIX38 – 45 REFERNCES46<br />THE HISTORY OF PLANE TABLE <br />The first known instrument for directly producing a drawing of a site was developed by Johann Richter. He is also known as Johannes Praetorius, a Nuremberg mathematician, born in 1610. This circular table, called a tabula praetoriana, mensula praetoriana or Pretorian table, used with a simple alidade and allowed a piece of paper to be slipped under the alidade for drawing.Later the devices adopted a rectangular table and enhanced the type and features of the alidade.<br />THE ORIGIN OF ALIDADE<br />1. An indicator or a sighting apparatus on a plane table, used in angular measurement. 2. A topographic surveying and mapping instrument used for determining directions, consisting of a telescope and attached parts. <br />There are a number of common usage's, the main subject of this web page is the map making surveying instrument used on a table that has been leveled.  On ships an Alidade is used to measure the angle from the ship's longitudinal axis to some target or targets, typically to help determine the ships position relative to the target(s).  Large telescopes have an alidade system that's used to point in azimuth.<br />These were used on a wooden table that had a drawing attached.  The idea was to make a map while in the field using stadia for distance to the rod.<br />Development<br />The very early Alidades were just a ruler with sighting wires held in a frame at each end.  That was what wasused on the Sketch Boards.  See the 1800s Brass and Army units below.<br />A compass can be used as an Alidade when a scale is aligned with the North position.  The Dietzgen Compass with square scale is in this catagory and you can get a scale base for some models of the Brunton Com-Pro pocket transits.<br />The K&E Early 1800s Alidade appears to be a transit instrument with a verticle angle measuring vernier capability and probably with stadia hairs in the scope so that distance can be manually computed for inclined shots.  No compass as part of the Alidade.<br />The Berger T-778, Gurley, K&E 5187A, K&E 53491, Lutz, Ottway Ealing No 92, San appear to be this type. <br />The Dietzgen 6220 & 6230 added a stadia computation scale "Beaman Stadia Arc" to the vernier making it much easier to compute the distance to the target.<br />The early Dietzgen seems to also have this capability.  TM 5-6675-211-15P for the Dietzgen 6220 & 6230 has change 2 dated 23 May 1973. <br />A number of the newer K&E Alidades use an optical scale like in a theodolite.  Optical scales increase the accuracy of measured angles as compared to reading a vernier.  The Watts and Wild Alidades may use optical scales.<br />The K&E 76 0000 adds what they call "self indexing".  <br />This is an auto level left145415function where the optical path is leveled by a pendulum when the bubble is within the outer ring of the level vial.  The reason for this is to save a huge amount of time when compared to older systems that need to have the table leveled for each shot.  This means that the table does not need to be accurately leveled.  This can be a problem if the Alidade is moved after the sight and before a reading.<br />Alidades were probably replaced by total stations since they can determine azimuth, elevation and distance all automatically, the latest versions work without retro reflection prisims on most targets.<br />In this close up photo of the K&E 5093A Scale you can see that when the alidade is level the Lower center vernier will read 30 degrees, not zero.  This is to avoid blunders which probably were common if level was 0 and there were + and -  numbers on both sides of 0 where a sign error would be a blunder.  Vertical angles from -30 deg to +30 deg can be read as 0 to 60 deg.  That is the limit of vertical angle measurements, since the rest of the scale is used for the horizontal and vertical distance factors.<br />On the left is the "HOR" vernier and on the right the "VERT" vernier.  These are used to convert the slant distance measured using the stadia method into horizontal and vertical distances.  When the alidade is level the HOR correction reads 100% and the vertical correction reads 50% (note you need to subtract 50 from the VERT reading to get the correction factor that's multiplied times the slant distance.<br />Notice that when the alidade is level all three readings are very much different.  Again, I'm sure this is to aviod blunders.<br />THE EXPENSION OF THE PLANE TABLE<br />Plane table mapping is a subject that has received minimum attention over the years, but it played a very important role in the history of surveying. The plane table dates to approximately the beginning of the 17th century. Some of the first references to the plane table are found in early survey textbooks. The early plane table was a mapping tool, as opposed to the compass and chain that was a boundary tool. The early plane table dealt mainly with planimetric features and not with vertical elevation. The use and development of the plane table has gone through four distinct changes since about 1600. I will address each one of these plane tables and its use. <br />THE FIRST PHASE-THE "PLAIN" TABLE<br />Figure 1. The first alidade was a ruler or scale of brass with fold-down sights.<br />The first plane table consisted of wooden boards placed together to form a table about 14 x 11" mounted on a tripod. A paper or cardboard sheet was placed on top of this board. The planimetric map or traverse was drawn on the paper. The alidade is the item that has gone through the most changes. The first alidade was a ruler or scale of brass with fold-down sights, about the same configuration as compass sights (see Figure 1). Note also the chain carriers. I do not know why they are such whimsical figures. <br />The following is a description of the first plain table from The Compleat Surveyor written in 1722 by William Leybourn. In the early text it was called a plain table, not a plane table. I have transcribed this just as it appears in the original text. For some reason, the letter "S" was written as an "F" before 1800: <br />A Defcription of the Plain Table, how it hath been formerly made, and how it if now altered, it being the moft abfolute Inftrument, of any other, for a Surveyor to ufe, in that it performeth whatfoever may be done either by Theodolite, Circumferentor, Peractor, Perambulator, or any other graduated Inftrument, with the fame eafe and Exactneff. <br />During its first phase, the early plain table was a tool that used intersection of lines to locate points that were plotted on the paper on the table. The early table did not have a level bubble but used the compass needle to level the table. If the needle was level to the table, this was close enough. The first operation was to orientate the table to north using the compass. The next step was to sight a point that needed to be located with the alidade and draw a line on the board. If the object was close enough to the table, then the distance could be chained. If chaining was not practical, then the point could be sighted from another location. This would give an intersection of lines, resulting in the location. Some of the early chains used with the plain table were only one pole in length-16.5'. The early plain table was used for mapping or cartography. The plain table was used for horizontal location; elevation was not a consideration in most cases. This item remained unchanged until about the middle of the 19th century. <br />THE SECOND PHASE<br />Figure 2. A 19th century plane table<br />The second phase brought about a name change from plain table to plane table. By the middle to the end of the 19th century, the instrument became in shape and size the plane table most surveyors would recognize (see Figure 2). The alidade now had a telescope. The table was about 2' square and was mounted on a tripod with an adjustable mount for leveling and rotating the table to orientate to north. The alidade had a vertical circle to turn a vertical angle and calculate the difference in elevation between points. <br />This is a description from 1935 by Harry Bouchard, an associate professor of geodesy and surveying at the University of Michigan, on why the plane table is a good choice for topographic mapping: "The plane table is one of the best instruments for topographic surveying, as with it the map is actually drawn in the field where the features can be seen and where the amount of detail to be mapped and the accuracy required can be judged to the best advantage. The topographer, while in the locality, can compare his finished work with the topographic features as they actually appear and thus ascertain if his map represents them properly." <br />Another good description of the plane table appears in the writings of Charles Davies from 1876: "The plane table is an instrument in which the manufacturer has combined the telescope of the transit with the straight edge and drafting board of the draftsman. When some form of stadia reduction arc is added to the vertical circle, the topographic engineer has an excellent field mapping instrument at his disposal." <br />During this second phase of the plane table, many different methods were developed to simplify the calculations to convert the slope distance to horizontal distance and the slope vertical angle to a vertical elevation. During the last half of the 19th century, the United States Geological Survey (USGS) put the plane table to use mapping vast areas of the western United States. Many national parks were mapped using a plane table. <br />Surveyors spent their entire careers bent over a plane table board. During this period, many improvements were made based on suggestions from field surveyors. One of these improvements was the Beaman Arc. The Beaman Arc was a system designed by William Beaman of the USGS. The Beaman Arc is a stadia reduction device, which is attached to the vertical circle of the alidade. Its design was based on the principle that for certain vertical angles the difference in elevation is a whole number multiple of the rod intercept, and the correction to be subtracted from the stadia (slant) distance to obtain the horizontal component is related to the vertical angle. This calculation was a simple multiplication for the horizontal distance using the Beaman "H" index. The vertical difference was a very similar operation using the "V" index on the Beaman Arc. The USGS set up simple standard forms to be used in the field to make these calculations without the use of sine and cosine tables. These improvements were all incorporated into the standard design of the alidades being sold by equipment companies. This alidade design remained unchanged for over 100 years (see Figure 3). <br />An article on the plane table would not be complete without mention of the stadia board. This was a level rod, about 10' or 12' long and 6" wide with very large letters. Many different styles of letters were tried on the face in search of a blunder-free combination. Many of the later stadia rods built by the survey equipment companies had handles on the back to hold the board and a built-in level bubble in order to plumb the rod. Most folded in half with a hinge in the middle for easy transportation. The faces of many of these rods have an art deco quality and are considered very collectable. One last thing about the stadia board; on a very windy day, the rodman could almost be lifted off the ground by a gust of wind while trying to plumb up the board. Surveyors earned their pay when wrestling a stadia board for eight hours a day. <br />PHASES 3 AND 4: THE MODERN ERA<br />Figure 4. Plane table mapping in the field.<br />Plane table mapping in the field.in the plane table setup and the point being read. Unfortunately-or fortunately-the total station with data collection made the plane table and alidade into museum pieces. <br />No article would be complete without a mention of the surveyors who utilized plane table boards (see Figure 4). There were only a few days each year suited for plane table mapping. The weather needed to be warm but not hot; sweat dripping from your face and hands could make a mess of the paper drawing. The USGS used an umbrella over the board when mapping. <br />Surveyors also needed a day with very little wind. And the reflection of the sun off the board would quickly turn your face into old shoe leather. In the winter, your fingers would get stiff from the cold, making it very difficult to draw the map. Bending over the board for eight hours each day without being able to lean on the table took a physical toll on the back. Despite these difficulties, some surveyors worked in ink in the field and produced maps that were nothing short of masterpieces. <br />Now you have the story of the plane table-gone but not forgotten. Technology is great, and we do need to move forward, but I can't help thinking we may have lost a little of what made a surveyor a surveyor when we lost the plane table.<br />INTRODUCTION OF THE PLANE TABLE<br />ABOUT THE PLANE TABLE<br />-<br />Figure 11-29.-Plane table.<br />When combined with the stadia board or Philadelphia rod, the plane table are used in or what is generally known as plane table surveys. With these instruments, the direction, the distance, and the difference in elevation can be measured and plotted directly in the field. The plane table operation produces a completed sketch or map manuscript without the need for further plotting or computing.<br />A plane table (fig. 11-29) consists of a drawing board mounted on a tripod with a leveling device designed as part of the board and tripod. The commonly used in leveling head is the ball-and-socket type. The cross section of a plane table with the tripod head is shown in figure 11-30(refer to the next. The board (G) usually is either 18 by 24 in. or 24 by 31 in. and has an attached recessed fitting that screws onto the top of the spindle (A). A wingnut (B) controls the grip of parts C and D on cup E. By releasing the wingnut (B), you can tilt the drawing board in any direction to level it. Another wingnut (F) acts only on the spindle and, when released, permits the leveled board to be rotated on azimuth for orientation. The tripod is shorter than the transit or level tripods and, when set up, brings the plane table about waist high for easy plotting. One precaution must be observed in attaching the plane table to the tripod head.<br /> <br />Figure 11-30.-Cross section of a plane table tripod bead.<br />A paper gasket should be placed between the fittings to prevent sticking or "freezing" of the threads. The plane table is setup over a point on the ground whose position has been previously plotted, or will be plotted, on the plane table sheet during the operation. The board is oriented either by using a magnetic compass for north-south orientation or by sighting on another visible point whose position is plotted. The board is clamped and the alidade is pointed toward any new, desired point using the plotted position of the setup ground station as a pivot. A line drawn along the straightedge that is parallel to the line of sight will give the plotted direction from the setup point to the desired point. Once the distance between the points is determined, it is plotted along the line to the specified scale. The plotted position represents the new point at the correct distance and direction from the original point. By holding the plane table orientation and pivoting the alidade around the setup point, you can quickly draw the direction to any number of visible points. The distance to these points is determined by any conventional method that meets the requirements for the desired accuracy and can be plotted along their respective rays from the setup point. Thus, from one setup, the positions of a whole series of points can be established quickly. For mapping, the difference in elevation is also determined and plotted for each point. The map is completed by subdividing the distances between points with the correct number of contours spaced to represent the slope of the ground.<br />The alidade (fig. 11-31) is a straightedge with a sighting device parallel to the edge. The more precise types have telescopes for sighting, special retitles for measuring distance, and graduated arcs for measuring vertical angles. A new version also includes a self-leveling, optical-reading system with enclosed graduated arcs.<br />1.The open-sight alidade (fig. 11-31, view A), which is very useful in sketching small areas, has a collapsible open sight attached to a straightedge. A level bubble is mounted on the straightedge for keeping the alidade level. A trough compass is also furnished for attaching to the sketch board. By sighting through the peep sight, the operator can determine a level line and the slope from the sighting point. No magnification is provided, so the sight lines are kept comparatively short. The distances can be estimated by pacing or can be measured with a tape if more accuracy is required. A 10-mil graduation that is numbered every fifth tick mark from 0 to 40 runs up on the right edge and down on the left edge of the front sight for determining slopes.<br />2. The telescopic alidades (fig. 11-31, views B and C) consist of straightedges with rigidly mounted telescopes that can be rotated through a vertical angle of ±30 0 . One type has a telescope set on a high standard or post to raise it above the table. This permits direct viewing through the telescope, which is at a comfortable height. The other type has the telescope mounted close to the straightedge. A right-angle prism is attached to the eyepiece and permits viewing through the telescope by looking down into the eyepiece prism.<br />3. The telescope for the high standard is 16 power; for the low standard, 12 power. Both are the inverting type with internal focusing. The prismatic eyepiece inverts the image top to bottom, so that it appears erect but reversed side to side. The line of sight through the telescopes in a level position is parallel to the straightedge on the base. The telescope reticle has horizontal and vertical cross hairs and a set of stadia hairs. As you already knew, the stadia hairs are used to measure distances. The vertical distance between the upper and lower stadia hairs is carefully read and multiplied by the stadia interval factor. This value is the straight-line distance between the instrument and the rod.<br />4. A circular bubble and a magnetic compass needle are attached to the base. These are used to level the plane table and orient it to its proper position. Since the ball-and-socket head does not permit as fine a movement as the leveling screw, the bubble is centered as accurately as possible. Then, the wingnut (fig. 11-30, view B) is set firmly but not tightly. When the plane table is tapped lightly on the proper corner, the operator can refine the leveling and then properly tighten the wingnut. To orient the plane table, loosen wingnut F and rotate the table. It is a good practice to draw a magnetic north line on the cover sheet or on two pieces of tape attached near the edges of the board. The straightedge is set on this line during orientation. When the plane table is rotated to face north, the magnetic needle is released and will have room to swing in its case without hitting the sides<br />5. The telescopic alidades have two other important features used for plane table surveying. These are the detachable striding level and the<br />Figure 11-31.-Types of alidades.<br />stadia arc. The striding level contains a long bubble, and when attached, permits accurate leveling of the line of sight. The bubble is mounted on a metal tube with V-fittings on each end. The fittings are placed astride the telescope and bear on built-in polished brass rings on each side of the center post. A spring clip on the level grips a center pin on top of the telescope and keeps the level from falling or being knocked off during operation. A button on the side of the level releases the clip for removing the level. For checking and adjusting, the level is reversible. The striding level normally is used to establish a horizontal line of sight and to use the alidade as a level. The stadia arc assembly consists of a vertical arc mounted on the end of the left trunnion and a vernier attached to the left bearing by an arm. A level vial is attached to the upper end of the arm; a tangent screw controls the movement of the vial. Once adjusted, this vial establishes a reference from which vertical angles can be measured even if the plane table is not exactly level. The stadia arc is a vertical scale attached to the alidade. With the stadia arc, it is possible to determine horizontal distances and differences in elevation by the stadia method.<br />6. A new model telescopic alidade is the self-leveling, optical-reading instrument. Instead of the exterior arc and level bubble, a prism system with a suspended element and enclosed arcs is used. As long as the alidade base is leveled to within one-half degree of horizontal, the suspending element (or pendulum) will swing into position. Then the vertical arc index that is attached to it will assume a leveled position. The scales are read directly through an optical train. This combination permits faster operation. In addition, there is no chance of forgetting to index the arc bubble and introducing errors into the readings.<br />7.Some of the auxiliary equipment used with a plane table consists of a coated plastic or a paper plane table sheet on which the map or sketch is drawn, drawing materials (scribing tools for coated plastic or pencils for the paper), scales for plotting distances, triangles, waterproof table covers, umbrella, and notebook. The plane table sheet is attached to the board by flatheaded, threaded studs that fit into recesses in the table and do not obstruct the alidade’s movement.<br />MORE ABOUT THE PLANE TABLE<br />A plane table is a device used in surveying and related disciplines to provide a solid and level surface on which to make field drawings, charts and maps.<br />This shows a plane table with part of the surface of the table cut away to show the mounting on the tripod. The mount allows the table to be levelled. On the table, the alidade with telescopic sight is seen.<br />A plane table consists of a smooth table surface mounted on a sturdy base. The connection between the table top and the base permits one to level precisely the table, using bubble levels, in a horizontal plane. The base, often a tripod, is designed to support the table over a specific point on land. By adjusting the length of the legs, one can bring the table to being approximately level regardless of the roughness of the terrain. <br />THE USE OF A PLANE TABLE IN REAL WORLD<br />The plane table is set over a point and brought it to precise horizontal level. A drawing sheet is attached to the surface and an alidade is used to sight objects of interest. The alidade, in modern examples of the instrument a rule with a telescopic sight, can then be used to construct a line on the drawing that is in the direction of the object of interest .By using the alidade as a surveying level, information on the topography of the site can be directly recorded on the drawing as elevations. Distances to the objects can be measured directly or by the use of stadia marks in the telescope of the alidade. Modern versions of the plane table are still used today for filling in or updating detail on street plans.<br />METHODS OF SURVEY: USING PLANE TABLE AND ALIDADE SURVEY<br />
      • This is a method of survey that allows a surveyor to plot and create an accurate scale drawing on site. The idea is to scale down the site to a size that fits onto the drawing board.
      • A plane table is a drawing board which is fixed to a tripod, levelled, and orientated. An alidade is a sighting device used to observe the salient points of the site.
      • Have a good look at the site before you start the survey, time should be taken to walk round and have a good look at the site or building that you are going to record. On a building, the obvious features that you would want to record are the corners, door and window openings, fireplaces. More subtle features that you would look out for are changes in wall direction, straight joints, blocked doors or windows, cruck slots, changes in the stonework, changes in floor covering, byre drains.
      SELECT A SURVEY STATION<br />
      • Once you have had a good look at the site, you will select a position for your survey station from which you have a line of site to as many of the main points as possible. It is particularly important to be able to see all the corners and places where a feature has a change in direction. Set up the tripod legs over your selected survey station. Prepare the drawing board , a piece of polyester drafting film is taped onto the drawing board with masking tape. The corners are taped first, with the film pulled tight, and then the edges are taped. The board is fixed onto the tripod.
      Orient the drawing board<br />
      • When drawing a building you would orientate the long side of the board so that it is parallel to the long axis of the building. If possible, for a site plan, you would oriented the board so that north is up the page. For all plans it is important to check that the whole site is going to fit on the board at your chosen scale. A pin is positioned into the board to give a fixed point from which observations and measurements can betaken. The pin marks the position of your survey station on the board. Once the survey has commenced the plane table should not be moved.
      Carry out the survey<br />
      • The alidade is placed against the pin and used to observe in turn, selected points. Rays are drawn on the film and measurements between the pin and the points taken with the 30m tape. The measurement is written onto the drawn ray as a record. Subsequently, each point is plotted along the ray at the selected scale, ' with a scale rule. Observations and measurements are taken to as many points as required to allow the shape to be recorded. These plotted points create an accurate framework around which the rest of the plan can be constructed. This method is most useful for plans of single buildings or small sites within a radius of 30m from the plane table.
      Larger sites<br />
      • For larger sites multiple stations will be required. The second station must be plotted accurately onto the plan from the first station and marked on the ground. It must lie within 30m of the first station.
      EQUIPMENT REQUIRED FOR A PLANE TABLE AND ALIDADE SURVEY<br />Plane table, tripod legs, alidade, spirit level, 30m tape, polyester drafting film, hi-polymer 6H pencil, masking tape, pin, scale ruler, compass, ranging rod for sighting, plumb bob.<br />EXAMPLE OF PLANE TABLE IS SET UP<br />EXAMPLE OF A DRAWING PAPER IS DRAWN AFTER THE ALIDADE SURVEY<br /> <br /> <br />MAPPING WITH A PLANE TABLE AND ALIDADE<br />First position of the plane table <br />attach a blank sheet of paper to the plane table<br />choose an appropriate scale according to the relative sizes of the mapping sheet and the study area<br />mark two base points (A' and B') on the paper corresponding to two ground positions (A and B) of known separation and relative location <br />position the plane table at A, placing the alidade along the line A'B' and turning the table with attached map until the A'B' line-of-sight coincides exactly with its corresponding AB line <br />without moving the plane table (even a slight shift in map orientation will cause errors), move the alidade so another field position, say C, can be sighted from A<br />a penciled line along the edge of the alidade will form a ray from A' toward a position that will become C'<br />in a similar manner, rays can be drawn toward other visible field objects <br />Second position of the plane table<br />position the plane table at B<br />place the alidade along line B'A' and turn the table and map sheet so the B'A' line matches the BA line-of-sight<br />if the B'A' line coincides exactly with the BA sighting line, then the map is oriented the same as it was at position A<br />now, rays drawn from B' toward C and D will intersect those drawn from A' <br />the intersections determine points C' and D' in the manner that a side and two adjacent angles always geometrically determine a triangle, i.e., by triangulation.<br /> Subsequent positions of the plane table<br />the researcher can move the plane table to position C because its corresponding map location is known, and therefore can repeat thc triangulations and extend the map data<br />moving to a third field position, whether or not it is necessary to view all targets, enables the mapper to verify the accuracy of the previous work<br />if the rays from three positions do not intersect at a single point, then the triangle of intersections represents the degree of inaccuracy of the map<br />three rays may not intersect at a common point if two, or all three, are almost parallel; thus rays that intersect at a very small angle generally should be avoided <br />OBSERVATION USING THE PLANE TABLE<br />Surveying and map making have always been two of the most interesting things a civil engineer has had to do. Surveying takes one out of doors, and is apt to lead him into the unknown and unexplored byways of the earth.<br />Though modern surveyors often use precise and expensive instruments, creditable surveys can be made with simple and inexpensive apparatus. Of such apparatus, two of the simplest are the plane table and the camera. Since one must know the principles of plane-table surveying before he can do camera surveying, this paper will describe the plane table alone, leaving the camera for another chapter.<br />A plane table is simply a drawing board mounted on a tripod so that it can be set up and worked upon in the field. One kind of plane table, which is used in the army for reconnaissance, does not even have a tripod; it is simply strapped to the arm of the man who is using it.<br /> HYPERLINK "http://amazon.com/gp/product/1425547931?ie=UTF8&tag=theultimatlearna&link_code=em1&camp=212341&creative=384065&creativeASIN=1425547931&adid=b92071c6-f0aa-4f8a-9cc1-9a9b533ff7c4" t "_blank" Plane-table maps vary greatly in scale and the area they represent. Landscape artists' plans may show only single city lots, while some topographic maps cover hundreds of square miles on a single sheet. For maps of a small farm, a park, or a residence block in the city, a plane table is almost ideal, since plane-table maps are made with rather simple apparatus and do not require much actual measuring on the ground. Most objects ,are located without ever going to. them, or even sending a rod-man to them.<br />Besides the plane table itself and a sheet of paper, only a small carpenter's level, a tape to measure a few distances with, and some spikes for markers, a hard lead pencil, a ruler, and a few needles are absolutely necessary for this sort of a map.<br />To start a plane-table map, a station must first be selected from which as many as possible o f the objects to be located on the finished map can be seen. Ordinarily, the objects one would locate are corners of buildings, fence corners, intersections of roads, corners of lots, banks of streams, possibly trees, and section and quarter section corners in the country. A railroad, a lake, a mountain, or anything which forms a noticeable landmark in / any particular locality, ought to be on the map. In mapping a territory which has never been surveyed before, toe first surveyor may name the hills and streams. After the first station has been selected, it is marked by a pile of stones, a stake, or, if precise work is to be done, a tack in the top of a stake. The table is then set up over this station point and leveled so that the surface of the paper will be truly horizontal. Generally, too, the board is "oriented," that is, placed so that two of its edges point north and south and two east and west. It is then clamped so that it will not move while working on it.<br />To begin the map, a point on the table is chosen to represent the station on the ground over which the table is set. This point is marked by sticking a fine needle into the paper, vertically. A small triangle should be drawn around the needle hole in the paper and labeled <br />"Sta. A," so that it will not be lost in the maze of points which will soon cover the sheet. <br />By sighting past his needle toward some object which is wanted on the map, like the corner of a house, its direction can be marked by setting another needle on the far side of the table, in line with the first and the given object. Then, if a ruler or straightedge be placed against these two needles and a fine line drawn connecting them, this line will show the exact direction of the object from other objects which are wanted on the finished map and can be seen from Sta. A are located by direction in the same way.<br />Station. A. <br />The first points to have their direction thus marked ought to be the next stations to be occupied. If all the objects to be located can be seen from three stations, or even two of three stations, three stations will be sufficient. The distance to one of them from Sta. A should be carefully measured and laid off to scale along its direction line on the map. Its place on the map should be marked exactly as the first station was, substituting B for A. It is wise, after every few sights at other objects, to take a sight along the line AB to make sure that the board has not turned. A good map is impossible if the board twists.<br />To measure the distance between stations, a 50 or 100-ft. tape, or some accurate substitute, is necessary. An ordinary piece of iron telegraph wire, 105 ft. long, is a good substitute. A No3 point, about 2 1/2 ft. from one end, is marked with a little lump of solder. A chisel dent in this solder will mark one end of the 100-ft. section. Then, with a borrowed tape or a good rule, measure off and mark every 10 ft., just as the first point was marked, until the entire 100 ft. have been laid off. The last 10 ft. should be divided into feet. In all this measuring and marking, the wire must be stretched out taut and straight. The extra 2 1/2ft. at each end are used for making handles. By estimating the tenths of a foot, measurements can be made with such a tape, or "chain," as an old-time surveyor might call it, just as accurately as they can be laid off on the map.<br />Ill: An Alidade, Consisting of Two Sights And a Straightedge, Takes the Place of the Two Needles<br />Two men are required for measuring, or "chaining," a head and a rear chainman. The rear chainman holds the 100-ft. end of the tape on the station point, while the head chainman takes his end forward toward the station to which they are measuring. When he has gone nearly the length of the tape, the rear chainman calls "halt." The head chainman stops and draws the tape up tight, while the rear chainman holds his division end on the starting point. Then the head chain-man sticks a spike into the ground to mark the place where his division end comes, calls out "stuck," and starts on toward the object point.<br />Large spikes make good marking pins, especially if they have little red or white strips of cloth tied to them. Surveyors use 11 markers. One is stuck into the ground at the starting point and is carried forward by the rear chainman, who also picks up the markers at each 100-ft. point as soon as the head chainman calls "stuck." In this way, the number of markers which the rear chainman has in his hand is always the same as the number of hundreds of feet which the last set marker is from the starting point.<br />In measuring between two points, care must be taken to draw the tape out taut and straight, its two ends must be level with each other, and it must be exactly in line with the two points between which the measurement is being made. In measuring downhill, one end may have to be held up high, and the point on the ground where the end division would come, found by dropping a stone from the place where it is in the air and watching for the spot where the rock strikes the ground. A surer way to do this is to hold a plumb-bob string on the last division and carefully let the bob down until it touches the ground. A rod with a red or white flag on it ought to be placed at or just beyond the point to which the measurement is to be made so that the rear chainman can easily line in the head chainman. The latter, before he places his marker, looks back to the rear chainman to be told whether or not he is "on line" with the object point. If he is not, and ought to go to the rear chainman's right to get "on," the latter holds out his right arm and the head chainman moves accordingly. When he reaches the right point, the rear chainman signals "all right" by holding out both of his arms and then dropping them to his side; the marker is stuck, and both move up a hundred feet and repeat the process.<br />After all the points possible have been located from Sta. A, and the direction lines labeled lightly in pencil so that they can be distinguished when the board has been removed from the station, the plane table is picked up and carried to Sta. B. Here it is again set up, leveled, and oriented by making the direction of the line AB on the paper exactly the same as that of the line from Sta. A to Sta. B on the ground. This is done by placing needles at points A and B on the table and then turning the board until the two needles and Sta. A are in line. Sights are taken on the same objects which were "shot" at Sta. A, and to objects which were not visible from Sta. A. The intersection of the lines of sight toward a given object from A and from B marks the location on the paper of that object. If the two ends of a HYPERLINK "http://amazon.com/gp/product/1555663907?ie=UTF8&tag=theultimatlearna&link_code=em1&camp=212341&creative=384065&creativeASIN=1555663907&adid=80f02546-70ff-400a-993e-0b27a63f1813" t "_blank" straight fence have been located in this way, a straight line joining the points will show the location of the fence on the map. By exactly similar methods, every other object is located on the paper.<br />In order to avoid errors, it is an excellent scheme to locate three stations near the outside edges of the area to be mapped, and locate all objects possible by sights from each of the three stations. If, instead of all three crossing each other at a point, the lines of sight from the three stations form a triangle, something is wrong. If the triangle is very small, it may be safe to use its center as the correct point; if not, the work must be repeated and checked. Locating even a few points by this method may prevent some bad blunders. The three stations ought to form as nearly as possible, an equilateral triangle; and the distances between all of them should be measured and laid out accurately on the plane table.<br />There are two ways in which the map may be finished, inked, or traced. By drawing in the "culture," that is, the things built by man, like the houses, the fences, the roads, and the railroads, in black ink ; the topography, that is, the hills and valleys, in brown; the water, in blue, and then erasing all the construction lines, a very neat map can be made. Another way is to get some "onion-skin" paper, or some tracing cloth, tack it over the penciled map, and trace the lines right through, using black India ink. This tracing can be blueprinted, just as a photographic film. A plain, neat title, describing location of map; who made it and when; the scale used; why It was made, if it was made for a special purpose, and the direction of the north point, ought to be on every map. The topographic sheets published by HYPERLINK "http://amazon.com/gp/product/B000112ISK?ie=UTF8&tag=theultimatlearna&link_code=em1&camp=212341&creative=384065&creativeASIN=B000112ISK&adid=e891f421-b223-4a37-89fd-ca9da4a2beaa" t "_blank" the United States Geological Survey are good samples to follow. They have been published for a great many places all over the country.<br />Ill: From an Original Drawing of a Survey of HYPERLINK "http://amazon.com/gp/product/B000EM8W9K?ie=UTF8&tag=theultimatlearna&link_code=em1&camp=212341&creative=384065&creativeASIN=B000EM8W9K&adid=74078b0b-c627-4f76-8736-83ad1791bf42" t "_blank" Mount Vernon, Made by George Washington at the Age of 14<br />Plane tables are almost as easily made as they are bought. If there is no old drawing board around the house, a new bread board from the ten-cent store will serve. For ordinary work, a table which is 15 or 20 in. square will do very well. The board must be mounted on a tripod so that it will be rigid while it is being worked upon and yet can be unclamped and oriented. A brass plate, with a hole in it and a nut soldered over the hole, screwed to the bottom of the board will permit the board and tripod to be bolted together in good shape. Another method, which is not nearly as good, is to drill a hole clear through the board, countersink it on top for a bolt head, and bolt the board and tripod head directly together. With HYPERLINK "http://amazon.com/gp/product/B000I1AY9S?ie=UTF8&tag=theultimatlearna&link_code=em1&camp=212341&creative=384065&creativeASIN=B000I1AY9S&adid=934c2556-8a73-435d-a18c-dc1b727e2b81" t "_blank" the brass plate and nut, the camera tripod can be pressed into service if a nut of the proper size has been used. The camera tripod is, however, apt to be wabbly with a drawing board on top; a much more satisfactory tripod can be built as shown in the accompanying drawings. Each leg is made of two strips of wood, 3/4 by % in. and 3 ft. long. These strips are screwed together at their lower ends, gripping a spike between them which will prevent the legs from slipping on the ground. The tops of the strips are spread apart and screwed to the opposite ends of an oak or maple cleat. This cleat is, in turn, screwed to the under side of the circular tripod head.<br />In place of the two needles and the ruler described for marking the line of sight, most plane-table men use an alidade, which is a combination of two sights and a straightedge. A very simple alidade may be made by mounting two needles on a ruler. The straight edge of the ruler is placed against the needle which marks the station at which the plane table is set up. Then, by swinging the ruler around this needle until its two sighting needles come in line with some object, the line of sight can be drawn directly on the paper along the edge of the ruler. A surveyor in India once made an alidade out of a piece of straightedge and two sights made of native coins hammered out by a native blacksmith. Two pieces of cigar box, one with a fine vertical saw slit in it, and the other with a vertical slot and a piece of fine wire or silk thread stretched down the center, glued to a well planed, straight, flat piece of wood, make a fine alidade. A careful worker may be able to put his sights on hinges so that they will fold down when not in use.<br />More than anything else, map making rewards care and accuracy, and shows up slipshod workmanship. If the pencils are sharp, the lines fine, and if the work is checked often, beautiful maps can be made with very simple apparatus.<br />White marks on waxed surfaces may be removed by rubbing lightly with a soft rag moistened in alcohol, after which rub with raw linseed oil.<br />STEPS TO AVOID ERROR DURING THE OBESERVATION USING THE PLANE TABLE<br />THE PROCESS<br />Establish a baseline (the baseline needs to be scaled to the project and features that are to be mapped need to be visible from the baseline.<br />Multiple baselines can be used as necessary but the second baseline must be correctly tied to the initial baseline.<br />The baseline can be extended to points plotted off the initial baseline. Extremely large areas can be mapped with a fair degree of accuracy using this method.<br /> STEPS TO AVOID ERROR<br />The plane table is set up over the initial point on the baseline.<br />Layout your paper so that it will easily contain the boundaries of the objects you are trying to map.<br />You will need to calculate the scale… 1” = 1 meter. The scale will determine how much shows up on your completed map. The scale needs to be appropriate (depends on the situation) <br />Use the Alidade (in our case triangular scale) to sight to the opposite end of the baseline.<br />Draw in the baseline.<br />If you can see it , then you can map it.<br />Sight across the plane table at features that will be located on your map. One end of the Alidade , will be on the initial point of the baseline, the other end will be exactly on the correct point, because light rays travel in straight line and your eyes are highly accurate.<br />Make sure you are using the same edge of the ruler (Alidade) each time.<br />CONCLUSION<br />As all we know that the use of total station have made the plane table and alidade into museum pieces because of the technology changes during 19th century .The aim of using the plane table is to show how the traditional way to use the alidade without the help of the theodolite and the total station while drawing and plotting the points on the drawing paper .We should be thankful because of the scientist that has made a lot of experiment during inverting the alidade and the theodolite to use with the plate table. Now, modern surveyor can use the total station as their main instrument but they will never forget what is plane table is about. <br />APPENDIX<br />This plane table was made by Benjamin Cole. Plane tabling is a method of survey which allows observations to be plotted directly on a map by a surveyor in the field. Modern versions are still used today for filling in or updating detail on street plans; in the 18th century it gave a rapid map without requiring the transfer of notes and measurements from a notebook.<br />Rudimentary plane table methods had been used in Europe since the early 17th century, but more advanced techniques and equipment for plane table mapping were first introduced to the United States by Ferdinand Hassler. Here, a plane table is used to map an area in Alaska.<br />Photo of a plane table and alidade , taken from Dewitt-Wallace Museum, U.S<br />Plane table alidade (1894). Image courtesy of National Oceanic and Atmospheric Administration Department of Commerce.<br />Instruments (plane table & alidade) owned by the US. Royal Engineers (Yorktown 225th)<br />Surveyor use the plane table during plotting the points on the drawing paper. <br />Image taken by the Coquetdale Community Archaeology.<br />Plane table surveying during excavation at the Ovenstones site.<br />Surveying at the North Pole<br />Debenham surveying with plane table on British Antarctic Expedition, 1910-1913.<br />