PROJECT GEODESYPROJECT GEODESY

SURVEY

SURVEY

In HYPACKIn HYPACK®® … …

Lat-Long on WGS-84

Lat-Long onLocal Datum

DatumTransformation

GPS

X-Y onProjection

GridConversion

Lat-Long on WGS-84

GPS

X-Y onProjection

GridConversion

On WGS-84 or NAD-83 projects:On WGS-84 or NAD-83 projects:

On other projects:On other projects:

The EllipsoidThe EllipsoidA mathematical shape that approximates the geoidal surfaceA mathematical shape that approximates the geoidal surface.

• Your position on Your position on the ellipsoid is the ellipsoid is defined by:defined by:– LatitudeLatitude– LongitudeLongitude– Height Above Height Above

EllipsoidEllipsoid

• Those items Those items change based on change based on the shape of the the shape of the ellipsoid!ellipsoid!

You are here

ɸ = Latitude

H

a = semi-major axis

b =

sem

i-min

or

axis

Flattening = (a-b)/a

Geoid: An equipotential surface, meaning the pull of gravity measured anywhere on the surface is a constant.

DatumDatum

When an ellipsoid is moved to fit your ‘local’ geoidal When an ellipsoid is moved to fit your ‘local’ geoidal conditions, it becomes a “datum”.conditions, it becomes a “datum”.

InternatioInternational nal

EllipsoidEllipsoid

EuropeaEuropean Datum n Datum 19501950

BogotBogota a

DatumDatum

Your datum will usually determine which ellipsoid is to be used.

North American Datum 1927: Clarke 1866 EllipsoidNorth American Datum 1983: GRS 1980 EllipsoidUK National Grid: Airy EllipsoidRiks Drihoek (Holland): Bessel 1841Hong Kong 80 Grid: InternationalJamaica Old Grid: Clarke 1880 Ellipsoid

Datum TransformationDatum TransformationConverting your position from one datum (usually WGS-84) to a local datum.Converting your position from one datum (usually WGS-84) to a local datum.

Φ’Φ

Your latitude, Your latitude, longitude and height longitude and height above ellipsoid above ellipsoid varies depending on varies depending on the datum being the datum being used.used.

The process of going The process of going from one datum from one datum (WGS-84) to another (WGS-84) to another datum is called a datum is called a “Datum “Datum Transformation”.Transformation”.

WGS-84

European Datum 1950 International Ellipsoid

Surveying on WGS-84 Ellipsoid?

Surveying on NAD-83State Plane

Coordinate System?

No Datum Transformation is

Required.

YESYES

No Datum Transformation is

Required.

YESYES

NONO

You Need to Do a Datum

Transformation!

NONO

For a Datum Transformation, you For a Datum Transformation, you can:can:• Determine your own parameters.Determine your own parameters.• Use published parameters.Use published parameters.• Use a Datum Shift model, if Use a Datum Shift model, if available for your area.available for your area.

Datum Transformations: Datum Transformations: Configurations

Don’t do a Datum Don’t do a Datum TransformationTransformation

Do a 3-Parameter Datum Do a 3-Parameter Datum TransformationTransformation

Do a 7-Parameter Datum Do a 7-Parameter Datum TransformationTransformation

Use a National Transformation Use a National Transformation ModelModel

Click here for available models:

Projections: Projections: A 2-D representation of the ellipsoidal surfaceA 2-D representation of the ellipsoidal surface

• Distortion is caused Distortion is caused when moving from the when moving from the ellipsoid surface to a flat ellipsoid surface to a flat project.project.

• BC BC B’C’ B’C’• A good projection should A good projection should

minimize the distortion.minimize the distortion.

1000 kg

A

B C

D

A’ B’ C’ D’

Typical ProjectionsTypical ProjectionsMercatorMercator Transverse Transverse

MercatorMercatorOblique Oblique MercatorMercator

Lambert Lambert Conformal Conformal

Conic IConic I

Lambert Lambert Conformal Conformal

Conic 2Conic 2

No distortion No distortion along along equator.equator.

No distortion No distortion along a line of along a line of longitude.longitude.

Good for N-S Good for N-S AreasAreas

Basis of UTMBasis of UTM

No distortion No distortion along selected along selected azimuth.azimuth.

For countries For countries not N-S or E-Wnot N-S or E-W

No distortion No distortion along a line of along a line of latitude.latitude.

Good for E-W Good for E-W areas.areas.

No distortion No distortion along two lines along two lines of latitude.of latitude.

A little bit of A little bit of distortion distortion between the between the lines.lines.

GEODETIC PARAMETERSGEODETIC PARAMETERS

• Each project has Each project has its own geodetic its own geodetic parameters.parameters.

• Create a new Create a new project or copy an project or copy an existing project:existing project:• Your new project Your new project

inherits the inherits the geodesy from the geodesy from the previous project.previous project.

Starting GEODETIC PARAMETERSStarting GEODETIC PARAMETERS

Click the ‘World’ icon.Click the ‘World’ icon.

Or… Click the ‘Preparation – Geodesy’ menu itemOr… Click the ‘Preparation – Geodesy’ menu item.

UTM GridUTM Grid

•Grids:Grids:•UTM North for UTM North for northern hemisphere.northern hemisphere.

•UTM South for UTM South for southern hemisphere.southern hemisphere.

•Zone:Zone:•Divided into 6Divided into 6º of º of longitude.longitude.

•Ellipsoid:Ellipsoid:•If your Ellipsoid is not If your Ellipsoid is not WGS-84:WGS-84:

•You have to do a You have to do a datum datum transformation.transformation.

NAD-83 GridsNAD-83 Grids

Grids:Grids:Select ‘State Plane Select ‘State Plane NAD-83’NAD-83’

Zone:Zone:Select the appropriate Select the appropriate state zone.state zone.

Ellipsoid:Ellipsoid:Even though NAD-83 Even though NAD-83 is based upon GRS-is based upon GRS-80, you will see WGS-80, you will see WGS-84 listed as the 84 listed as the ellipsoid. This is ellipsoid. This is because the US because the US government treats the government treats the two as the same, even two as the same, even though there are though there are slight differences.slight differences.

NAD-27 GridsNAD-27 Grids

Grids:Grids:Select ‘State Select ‘State Plane – NAD27’Plane – NAD27’

Zone:Zone:Select your state Select your state plane zone.plane zone.

Ellipsoid:Ellipsoid:Fixed to ‘Clarke Fixed to ‘Clarke 1866’.1866’.

You have to do a You have to do a Datum Datum Transformation!Transformation!

Set the Datum Set the Datum Shift file to Shift file to CONUS.CONUS.

UKNGUKNG

Grids:Set to ‘UK National

Grid’Zones:

There are no zones!

Ellipsoid:Fixed on ‘Airy’.

You have to do a Datum Transformation.

Set the Datum Shift file to OSTN02.

User Defined ProjectionUser Defined Projection

Grids:Grids:Set to ‘None’ Set to ‘None’ (bottom of list).(bottom of list).

This opens up the This opens up the Projection items.Projection items.

Projection:Projection:Select your Select your projection.projection.

Enter the Enter the projection projection parameters.parameters.

Ellipsoid:Ellipsoid:If not WGS-84, do If not WGS-84, do a Datum a Datum Transformation.Transformation.

RTK Tide CalculationRTK Tide Calculation

• User Defined RTK CalculationUser Defined RTK Calculation• Choose from which source the K value is based uponChoose from which source the K value is based upon• Check the RTK TIDES presentation for detailsCheck the RTK TIDES presentation for details

Geodetic Parameters: Geodetic Parameters: Other StuffOther Stuff

Geoid Model:Geoid Model: Used in RTK Tides methods.Used in RTK Tides methods.

Orthometric Height Correction:Orthometric Height Correction: Used in RTK Tides method.Used in RTK Tides method.

VDatum Zone and Chart Datum:VDatum Zone and Chart Datum: Used in VDatum RTK TIDE Used in VDatum RTK TIDE

MethodMethod

Local Grid AdjustmentLocal Grid Adjustment Used to convert to local Used to convert to local

engineering grid.engineering grid. Has its own presentation!Has its own presentation!

Chart datum level above Chart datum level above geoid.geoid. Formerly the Orthometric Formerly the Orthometric

Height Correction….Height Correction….

Time Variable Datum Transformations

To account for continental drift, time variable transformations are available for select locations. Select the ITRF/WGS84 Epock, the target system, and the target year. Click OK, and the transformation parameters are calculated.

In GEODETIC PARAMTERS, click “Tools” and then select the “Time Variable Transformations” menu item.