Local X,Y to Long,Lat

Use the Coordinates > Georeferencing > Local X,Y -> Long,Lat menu option (XY2LL GX) to convert local X, Y coordinates to longitude, latitude coordinates based on a common known location and the direction of the local coordinate system.

The script parameters are the same as for the LL2XY GX, so that an inverse conversion can be performed without changing parameters.

There are two dialogs for this option. The first dialog enables you to select the input and output channels, and the second dialog is used to set the conversion parameters.

Local X,Y -> Long,Lat dialog options

Local X channel

The name of the local coordinate X channel.

Script Parameter: LL2XY.X

Local Y channel

The name of the local coordinate Y channel.

Script Parameter: LL2XY.Y

Longitude channel

The name of the existing longitude channel.

Script Parameter: LL2XY.LON

Latitude channel

The name of the existing latitude channel.

Script Parameter: LL2XY.LAT

Convert Local (X,Y) to (Longitude, Latitude) dialog options

Local X

The local X coordinate.

Script Parameter: LL2XY.LOCX

Local Y

The local Y coordinate.

Script Parameter: LL2XY.LOCY

Local length units

The local length units selected from POSC compatible abbreviations. Normally "m" or "ft".

Script Parameter: LOOKUP1.UNITS

Local grid Y direction (deg azimuth)

The direction of the local grid Y axis in degrees azimuth (clockwise) from geographic North.

Script Parameter: LOOKUP1.AZM

Longitude of local (X,Y)

The longitude of the local (X,Y) coordinate.

Script Parameter: LL2XY.LOCLON

Latitude of local (X,Y)

The latitude of the local (X,Y) coordinate.

Script Parameter: LL2XY.LOCLAT

Application Notes

This procedure is useful if you have data points with known longitude and latitude coordinates, and you would like to work on a map/local X, Y coordinates.

  • For the "Projected" method, the X, Y coordinates are calculated based on a projected map coordinate system by running NEWXY GX.

  • For the "Local" method, the X, Y coordinates are calculated by projecting longitude/latitude coordinates to a Transverse Mercator projection with a central meridian through the specified local (X, Y) and then rotating to the required Y azimuth by running LL2XY GX. A local coordinate system is an arbitrary Cartesian coordinate system that has been located and oriented for the purposes of a particular study.