Defining an NEZ coordinate system based on known scale and angle
September 19, 2011 Leave a comment
Some of you may wish to display the Feature coordinates in reference to a local Cartesian coordinate system. For example, you may wish to express the location of the buildings, wells or towers on a large complex in terms of their X-Y position with respect to a reference location on the campus. The reference location coordinates are usually set to values that permit all the locations on the resultant map to be expressed with positive X and Y values. For instance, if the map spans an extent of about 3500 ft both ways, and the reference location is set near the center of the campus, then the reference position could be assigned a value of (2000, 2000).
The local coordinate system is called an NEZ coordinate system with the N (Northing) corresponding to the Y value, the E (Easting) corresponding to the X value, and the Z (Z-value) corresponding to the vertical distance along the Z-axis.
The relationship between the LLA plane and the NEZ plane consists of a rotation and a scale change. How would you transform the LLA coordinates to the NEZ coordinates? Leave the computations to the software program, but you will need to pick the reference location and specify the relative orientation and the scale for the NEZ coordinate system.
If you are using a known local control point and the associated transformation angle and scale values, you can enter this information into your iCMTGIS II or your iGPSGIS II for your newly defined NEZ plane as follows.
From the Main Menu, select Setup then select Coordinate System. Select NEZ , tap the Edit button then enter a name for your new plane.
Tap in the first data field under the GPS Reference section. Enter the LLA coordinates of the reference control point, or tap the Pick button then select the reference point from Map View if that point has been digitized in Map View.
Enter the decimal values for the Angle and Scale fields. Save your settings then return to Map View. When you tap on the map, you will see that the coordinates are now displayed in terms of the NEZ system.