Photogrammetry is a technique for obtaining reliable spatial information about physical objects through analyzing photographs. It involves taking overlapping aerial photographs from aircraft and processing them using software to extract 3D spatial data like digital elevation models, contours, and orthophotos. The key aspects are that it is precise, cost-effective, produces 3D representations, and relies on established algorithms to extract data from overlapping photos with less manual effort than traditional surveying methods.

1. PHOTOGRAMMETRY
G.CHANDRA SEKHAR REDDY
M.Tech(GIS)
NIIT UNIVERSITY

2.  VERY PRECISE
 3D REPRESENTATION
 TIME EFFECTIVE
 COST EFFECTIVE
 BASED ON WELL ESTABLISHED AND
TESTED ALGORITHMS.
 LESS MANUAL EFFORT
 MORE GEOGRAPHIC FIDELITY

3.  Photos – light
 Gramma – to draw
 Metron – to measure
“Photogrammetry is the technique of measuring objects
from photographs”
“The art, science and technology of obtaining reliable
spatial information about physical objects and the
environment through the processes of recording,
measuring and interpreting image data.”

4. Aerial Photogrammetry the camera is mounted
in an aircraft and is usually pointed vertically towards
the ground. Multiple overlapping photos of the ground
are taken as the aircraft flies along a flight path. These
photos are processed in a stereo-plotter (an instrument
that lets an operator see two photos at once in a stereo
view). These photos are also used in automated
processing for Digital Elevation Model (DEM) creation.
Close-range Photogrammetry the camera is
close to the subject and is typically hand held or on a
tripod. Usually this type of photogrammetry work is
non-topographic - that is the output is not topographic
products like terrain models or topographic maps, but
instead drawings and 3d models. Everyday cameras are
used to model buildings, engineering structures,
vehicles, forensic and accident scenes, film sets, etc.

5. PROCESS
FLOW
=> RAW DATA FORM CLIENT
=> AERIAL TRIANGULATION
=> DATA CAPTURING
=> DEM GENARATION
=> CONTOUR GENARATION
=> ORTHOPHO GENARATION
=> GIS CONVERSTION

6. In Aerial Photogrammetry the camera is mounted
in an aircraft and is usually pointed vertically towards
the ground. Multiple overlapping photos of the
ground are taken as the aircraft flies along a flight
path. These photos are processed in a stereo-plotter
(an instrument that lets an operator see two photos at
once in a stereo view).

7. AERIALTRIANGULATION
Aeotriangulation
adopts
photogrammteric
triangulation which
establishes the
geometric
relationships among
overlapping and
sidelapping
photographs to
determine
supplemental
horizontal and vertical
control points

8.  Adjacent but
overlapping aerial
photos are called
stereo-pairs and
are needed to
determine parallax
and stereo/3D
viewing

9. R u n #1
R u n #2

10.  Overlapping
photography
 Endlap - ~60%
 Sidelap - ~20-30%

11. PLANIMETRIC FEATURE
EXTRACTION

12.  Buildings
 Transportation Features
 Hydro Features
 Utilities
 Vegetation
 Breaklines
 DTM points
 Bridges

13. Raster data are described by a cell grid, one value per cell
Vector Raster
Point
Line
Zone of cells
Polygon

15. 15

16. PLANMETRIC FEATURES

18.  There is no common usage of the terms digital
elevation model (DEM), digital terrain model
(DTM) and digital surface model (DSM) in
scientific literature.
 In the most cases the term digital surface model
represents the earth's
 The digital terrain model represents the bare
ground surface
 The term Digital Elevation Model is often used as a
generic term for DSMs and DTMs, only
representing height information without any further
definition about the surface

19.  There is no common usage of the terms digital elevation
model (DEM), digital terrain model (DTM) and digital
surface model (DSM) in scientific literature.
 In the most cases the term digital surface model
represents the earth's
 The digital terrain model represents the bare ground
surface
 The term Digital Elevation Model is often used as a generic
term for DSMs and DTMs, only representing height
information without any further definition about the surface

21.  Contour lines are lines drawn on a map connecting
points of equal elevation
 Contour lines are useful because they allow us to show
the shape of the land surface (topography) on a map
 This vertical spacing is referred to as the contour interval
 If the contour interval is 10 ft. Each the contour lines was
a multiple of 10 ft.( i.e. 0, 10, 20, 30)
 In areas with high relief the contour interval is usually
larger

23. DATA FOR THE 3D CITY MODELS
 The 3D city models contain data, which is related to the Spatial objects.
Those objects are generally topography, buildings, transportation,
plant cover, infrastructure and other details related to the goal of
application.
3D city models are focused on buildings however it may contain
roads, green cover, trees etc. according to the usage of model.

24. 3D BUILDING MODEL
The constructed 3D model

25. Photogrammetry …. Lecture 11
Dr. Steve Ramroop

26. ORTHO PHOTO GENARATION

27. ORTHO PHOTO GENARATION
Usually orthoimages do have some geometric limitations, they do
show only the elements located in the height level of the used DEM in
the correct location. Buildings not included in the DEM, are shifted with
the location of the roofs depending upon the tangent of the nadir angle
of the image location multiplied with the building height. So also parts of
the facade can be seen If the height value of the roof is included in a
detailed DEM, the roof is shown in the correct position corresponding to
an orthogonal map projection. This is causing the problem that for some
parts, before hidden by the roof, no information is available for the
orthoimage

28. ORTHOIMAGE
location of a building in a usual
orthoimage with the
orthoimage based on a DEM the bare
corrected location of
including ground
the building roof

29. ORTHOIMAGE
location of bridges uncorrected and corrected for
height differences against the road below

30.  The output of photogrammetry is typically a
map, drawing or a 3d model of some real-
world object or scene. Many of the maps we
use today are created with photogrammetry
and photographs taken from aircraft.