explain datum

2. • Adatum is an)' numerical or geographical
quantity or set ofsuch quantities. which
may serve as a reference Of base for other
quantities.
• In surveying (or geodesy), datum is a set of
quantities that describe the shape, size,
rotation and gravity field parameters ofthe
Earth.

3. Geodetic Datum
• l...oca.l l regional datum
• Approximate size and shape of the earth on
• local •regional scale
• Geometrical center ofthe ellipsoid not
necessarily coincident with the &eO center
• Geodetic datum is suited to the surveyina
area they were defined where there are
inadequate global salellite surveying
systems

4. • Geodetic datum define the reference systems that
describe the size and shape ofthe earth.
• Hundreds ofdiffeRnt datum have been used to
frame position descriptions since the flf'St
estimates ofthe earth's size were made by
Aristode.
• Datums have evolved from those describing a
spherical earth to ellipsoidal models derived from
years ofSlIellite measurements.

5. > ConsIsts 01 +
.k or an initial origin:
> Tho _lor one h:
)0 The pararnrMeB d!he retelence ~
> and Ihe geoid _ _ ItIhe origin. II
> Tho _ 0I1he _ and geoIckpheroId
_ _ .. set to zero It an origin point ____
> ~ JoIlnson in Auslnllan datum

6. - ~ The elipsoid Is ImpIIcIUy inl.od 10 the daUn. SO k has
become comnon 10 use the dalum name10 nwthe
sp/leroId IWld W;o ..... ox~ WOOd Geodetic
System 84 (WGS84).
~ The orionIationlWld scale of the...-Is doIIned
usilg UIlor goode4ic observIIions.

7. Geodetic datum
- ---......•

8. Geodetic Datums: Datum Types
• Datum types include horizontal, vertical and
complete datum (3-D Datum).
Horizontal Datum
• Examples horizontal datum include the North
American Datum of 1927 (NAD21) and the
European Datum 19S0 (EDSO).

9. Geodetic Datums: Datum Types
Vertical Datum
• Examples vertical datum include the National
Geoc!etk V",lcaI DoIum of 1929 (NGVD29) and
the North American Vertical o.turn of 1918
(NAV088).
• Some are bMed on sea-Ievel measurements and
leveling networks (NGVD29). others on gravity
measurements (NAYOU).

10. 3-D Datum
• The GLobal Positioning system is btsed on the
World Geodctk System 1984 (WGS-I4).
Example:
• In order to design and construct highway
proj_ all distaocos (boIb horimntal and
vertical) must be referenced to a recognized
_m.

11. A JeOdetic datum is comprised oftwo surfaces
that approximale the ral Earth.
• The rustofthese surfaces is an ellipsoid that
mathematically approximales the shape and size
ofthe Earth. The ellipsoid is used as a reference
frame for horizontal position computations.
• The se<:ond surr.cc is the geoid that is a
mllthetMticaUy imaulat' surface ofelevation
zero. The geoid is used for determining
elevations or Vt'I'tical position.

12. Malaysia :- Datum
• JUPEM is responsible for
- the establishment and mlliotenance ofborizonlll and
verticaJ control points for aeodecic 19P1ications.
• Geodette datum for mapping
- Geodetic o.tum ofMalaysia, 2000 (GDMlOOO)
• ..ntr. the ... ofGPS tcIdIy. conwrsq froaI WGS14 10
ClDM2000 m.de ....
• Mapping projection we use
- RSO (Rectified Skew Orthomotpbic Projection System)
or the BBST ·Bcntuk Benar Sistcm di Tepllti

13. • A horizontal datum is a surfilce of constant
values which fonns the basis for the
computations ofhorizontal control surveys
in which the curvature ofthe earth is
considered.
• A reference ellipsoid is used for a
horizontal datum..

14. Five parameten are required to defme a horizontal
datum:
2 - '" specify the di.mensioos ofthe ellipsoid.
2 • '" specifY the kation ofaD initial poiDt (ariaia)
I • '" lpeC:ifY the orie....dOIl. (i.e. DOItb) ofthe coordinate
."'....
• Countries. or groups ofcountries
- ct.oo. differeo.t reference ellipsoids '" minimize the
deviMions bdwtn the topoaraphy IDd the ellipsoid In
the", rePoo (best·fit ellip30id for their rea,ion.).
•

15. .....MllfII
....... 111.
,...u11tM.

16. • Those Individual geodetic datums ant
often leferred to as local dat.ma.
• Since the odwnt of GPS. the tendency 10
to adopt a gIOOal datum that provides the
best tit lor the entire Earth.
• Global datums are also related to the
e.rth's centermaas, the geocenleJ.

17. • Positions of points (coordinates) on a
horizontal datum are expressed in terms of
latitude and longitude.
• Topics In cartography, surveying, navigation,
and astronomy .11 mBa Ule of geodetic
datums.
• Datum is importllnt because refef'encing
geodetic ooord6n8tee to the wrong datum can
result in position en'Ors of hundreds of meters
• It is used to Identify ~. in geographic
information systems, ~ positioning
systems, and nilvigation systems

18. • VERTiCAl datum based on a local
geoid definition (at one Of more tide
gauge, or "vertical datum" stations).
• Elevations for engineering projects must
be referenced to a singfe vertical datum
so various phases of a project, and
contiguous projects, will match.

19. • This datum can bo bosed on some particular
standard, such as sea level, an assumed
e~yation or the _vatIon of a local permanent
point or naturat object.
• Various organizations (private and public),
use datums that belt serve their Individual
needs.
• This has led to many different datums.
causing a considerable amount of confusion.
• The diversity of datums in use today and the
technological advancements that have made
possible global pos~lonlng measurements
. ,

20. • This requires careful datum setection and
careful converskln between COOfdinates in
different datums.
• GeOOetic datums and the coordinate
reference systems based on them were
devekiped to describe geogl1lphlc positions
(orsurveylr!; . . .jillion.

22. • Using a 'geodetic datum', any point on the
earth's surface has an x, y, z coordinate
value. and that coordinate value can be
In>nslated into a Latitude (~). Longitude (')
and a HeIght (h) 1IboYe. on Of even below
the IUrface of the mathematical model
• ~ datu"" are used lor hOOzontal
poaItioning only.
• The _ I component is traditionally
referred to mean sea level. Elevations are
related to the geoid.

23. • The "figure of the earth" was refined from
tlal.....rth models 10 opherlcal model, of
suf!icienl accuracy 10 allow global
oxpionltion, navigation and mapping,
• Flat earth models are still used for plane
surveying. over distances short enough so
that earth curvature Is Insignificant (tess than
10km

24. • Spherical earth models represent the shape
of the earth with a sphere of a speclfoed
radius.
• SpheriCal earth models are often used for
short range navigation and for global distance
approximations
• E!ipsoidalearth models are required !of
accurate range and bearing calculations
over long distances.

25. • Loran-C, and GPS navigation receivers use
ellipsokial earth mod. to compute position
and way point Infonnotion.
• Blipsoldal models define an ellipsoid with an
equatorial radius and • polar radius.
• Reference ellipsoids ore usually defined by
semknajor (oquatoriol radius) and ttattenlng
(tho retotionshlp _en oquotoriol and polar
radII).

26. Global Coordinate Systems
Coordinate systems to specify locations on
the surface of the earth have been used for
centuries.
• In __ geodesy !he equalOr, !he Iroplcs
of Cancer and Capricorn, and !hen lines of
latitude and longitude wen! used to locate
pooIIions on !he aarth.
• EasIom cartographen used other
rectangular grid systems as oarty as 270 A.
D.

27. Latitude, Longitude, and Height
The most commonty used coordinate
system today Is the Lolltude, longitude, and
height system.
• The Prime Meridian and the Equator are the
reference planes used to define latitude and
longitude.
•

28. Equator and Prime Meridian
• The geodetic latitude of a point is the anglo
from the equatorial plane to the vertical
direction of. line normal to the reference
oiIlpSQid.
• The geodetic longitude of a point is the anglo
between a reference plane and 8 plane
passing through the point, both planes boIng
porpondicular 10 the oqualaWl plano.
• The good.1ie height at a point Is the
distance from the reference ellipsoid to the
point In a direction normal to the ellipsoid,

29. • Earth Centered, Earth Fixed Cartesian
coordinates are afao used to define three
dimenalonal poaItions.
• Earth centered. Hrth-fixed. X. Y. and Z.
Ca_lan c:o<>f<Ilnates (XYZ) define lllree
dimensional poaltlons with respect 10 tho
center 01 moss of tho reference ellipsoid
• The Z-axle points toward tho North Pole.
• The X-axia Ie deljned by tho Intersection of III.
plane define by tho prime meridian and tho