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Adding Custom Coordinate Reference Systems

LizardTech Express Server can reproject imagery into an EPSG-defined coordinate reference system (CRS). The supported EPSG codes are a subset of those which were defined by the EPSG database available at the time the product was released. You can add support for other CRSs, such as custom projections or more recent additions to the EPSG database. To do this you must obtain an OGC-compliant well known text (WKT) version of the CRS and add it to the esri_extra.wkt file used by Express Server.

Improper editing of the esri_extra.wkt file can cause unexpected behavior. Please review your changes carefully and make a backup before you start.

Obtaining an OGC-Compliant WKT Version of the CRS

The WKT version of the CRS should be available from the source of the CRS. If an ESRI ".prj" file is provided instead (as is often the case) the .prj file can be converted in LizardTech GeoExpress using the steps below.

To obtain an OGC-compliant WKT version of the CRS:

  1. Add any image to the Images tab of the Job list in GeoExpress.
  2. Choose Reproject from the Tools menu. The Reprojection Manager appears.
  3. Click Select Coordinate Reference System. The Coordinate Reference System Selector dialog appears.
  4. Select the Use custom WKT checkbox.
  5. Choose Add a new WKT from the Select WKT drop-down menu. The Edit User Defined WKT dialog appears.
  6. Click Browse to choose the .prj file you need to convert. If you don't see your file, select ESRI CRS files (*.prj) in the Files of Type drop-down menu.
  7. Click OK. The text box populates with the OGC-compliant WKT that you will add to the esri_extra.wkt file.
  8. Copy the WKT and paste it into a text editor for later use.
  9. You may now close GeoExpress without saving the project.

If you don’t have access to GeoExpress or an authoritative conversion of your projection string (from the source) you may be able to convert it "by inspection" as ESRI PRJ files are quite similar to WKT files (see example below).

Adding the WKT to the esri_extra.wkt File

This text file is used internally by Express Server. Each line in the file follows the format

epsg code, wkt

containing an EPSG code with a definition of an OGC-compliant (but presumably non-standard) CRS.

To add the WKT to the esri_extra.wkt file:

  1. Using a text editor, open the esri_extra.wkt file (located by default in <Express Server installation directory>/ImageServer/etc/gdal).
  2. Add a new line for your custom EPSG code to the bottom of the file as follows:
    1. Add the custom EPSG code and a comma
    2. Append the WKT. Remove all the carriage return line feeds so that the WKT is all one long string.

Example

Here we’ll add support for EPSG code 102763, which is not in the EPSG database and not supported by Express Server. It comes from the following custom ".prj" file:

PROJCS["NAD_1983_StatePlane_Kentucky_FIPS_1600_Feet",
GEOGCS["GCS_North_American_1983",DATUM["D_North_Am
erican_1983",SPHEROID["GRS_1980",6378137.0,298.257222
101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.017453292
5199433]],PROJECTION["Lambert_Conformal_Conic"],PARAM
ETER["False_Easting",4921250.0],PARAMETER["False_Northi
ng",3280833.333333333],PARAMETER["Central_Meridian",-8
5.75],PARAMETER["Standard_Parallel_1",37.0833333333333
4],PARAMETER["Standard_Parallel_2",38.66666666666666],
PARAMETER["Latitude_Of_Origin",36.33333333333334],UNIT
["Foot_US",0.3048006096012192]]

Convert the .prj file to an OGC standard WKT using GeoExpress, which results in the following. Note that the DATUM and PROJECTION values have been changed.

PROJCS["NAD_1983_StatePlane_Kentucky_FIPS_1600_Feet",
GEOGCS["GCS_North_American_1983",
DATUM["North_American_Datum_1983",
SPHEROID["GRS_1980",6378137.0,298.257222101]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]],
PROJECTION["Lambert_Conformal_Conic_2SP"],
PARAMETER["False_Easting",4921250.0],
PARAMETER["False_Northing",3280833.333333333],
PARAMETER["Central_Meridian",-85.75],
PARAMETER["Standard_Parallel_1",37.08333333333334],
PARAMETER["Standard_Parallel_2",38.66666666666666],
PARAMETER["Latitude_Of_Origin",36.33333333333334],
UNIT["Foot_US",0.3048006096012192]]

Add the new WKT to the esri_extra.wkt file, preceding it with the EPSG code and a comma. While the text in the sample below has line breaks, the text in your esri_extra.wkt file should be on one line with no breaks.

102763,PROJCS["NAD_1983_StatePlane_Kentucky_FIPS_1600
_Feet",GEOGCS["GCS_North_American_1983",DATUM["North_
American_Datum_1983",SPHEROID["GRS_1980",6378137.0,29
8.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.017
4532925199433]],PROJECTION["Lambert_Conformal_Conic_2
SP"],PARAMETER["False_Easting",4921250.0],PARAMETER["Fa
lse_Northing",3280833.333333333],PARAMETER["Central_Meri
dian",-85.75],PARAMETER["Standard_Parallel_1",37.08333333
333334],PARAMETER["Standard_Parallel_2",38.666666666666
66],PARAMETER["Latitude_Of_Origin",36.33333333333334],U
NIT["Foot_US",0.3048006096012192]]

Express Server will now reproject to "EPSG:102763".