STAR*NET V6 - Circe

Chapter 10 Adjustments in Grid Coordinate Systems
10.12 Defining “Custom” Grid Zones
Parameters for Custom zones are stored in a text file named STAR6.CUS located in the
same directory you installed STAR*NET. It contains ellipsoid parameters, custom grid
zone parameters, and optional custom linear units information. A listing of the supplied
file is shown later in this section. This file is a standard text file, and using any text
editor, you can view it or modify its contents to add ellipsoids, grid zone parameters or
linear unit definitions as needed. When running STAR*NET, this information becomes
available in the Project Options/Adjustment dialog.
Below are descriptions of the three sections in the STAR6.CUS file. While reviewing
these descriptions, refer to the listing of the supplied file.
Ellipsoids
This section contains a list of ellipsoids available for custom grid zones and UTM. Most
standard ellipsoids used internationally are supplied in the file, but you can edit-in other
special ellipsoids whenever required.
A data line defining an ellipsoid begins with the “E” character. As an example, we’ve
supplied a special non-standard ellipsoid “Airy Modified” as the second ellipsoid in the
list. (It’s actually used in Ireland.) An ellipsoid name may contain up to 18 characters
including internal blanks, and is terminated by a “:” colon character.
Note that even though ellipsoids for the United States NAD grid systems are included in
this list, when using NAD27 and NAD83 the program uses built-in ellipsoidal constants
for these zones so they can’t be inadvertently changed by editing this file.
Custom Grid Zone Parameters
This section contains parameters for any custom zones defined. Projections currently
supported by STAR*NET are Transverse Mercator, Lambert and Hotine. A few custom
zones which illustrate parameters required for the different projections are already
included in the file, and of course you can edit-in custom zones required for your own
geographical area. Parameter lines defining Transverse Mercator zones begin with a “T”
character; Lambert, with an “L” or “B” character; and Hotine, with an “H” character. See
the attached listing of the STAR6.CUS file for data items required for each kind of line.
Note that you can enter Lambert parameters using two methods. The “L” code allows
entry of a single parallel and the scale factor on that parallel, the method normally used
internationally. The “B” code allows entry of two standard parallels, the method used in
the United States and sometimes elsewhere. The zone illustrating the “B” code file
shown in the sample STAR6.CUS listing actually includes the same parameters used for
the definition of NAD83 California Zone 0403.
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