ESRI Projection Engine Reference

As of ENVI 4.7, all calculations involving map projections in ENVI are handled using the powerful ESRI Projection Engine. This is true for all ENVI products, including ENVI, ENVI+IDL, ENVI Zoom and ENVI Ex. Previous versions of ENVI used the General Cartographic Transformation Package (GCTP). While much of ENVI's map projection functionality will remain unchanged to users, the switch will result in some differences when working with map projections in ENVI 4.7 and later versions. This help article provides links to files containing information needed when performing the following tasks:

• How to use a projection type that the ESRI Projection Engine supports but ENVI does not.
• Using a datum or projection type that is *not* supported by the ESRI Projection Engine.
• Specifying a different method for datum shifts.
• Creating a log file that can be used for debugging projection problems.

Exelis VIS Technical Support plans to add help articles with step by step instructions for these tasks in the future. In the meantime, if you need to perform any of these tasks, you may find it most helpful to contact Technical Support for instructions.

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ENVI Map Projection Engine Articles

Note : ENVI switched from using version 9.3 of the ESRI Projection Engine with ENVI 4.7 and 4.8, to using version 10 with ENVI 5.  Therefore, the steps used for various map projection related tasks are different in ENVI 4.7 and 4.8 than in ENVI 5.

ENVI 4.7 and 4.8

Title: Defining ENVI Map Projection Engine Geographic Transform Overrides
Description: How to override the default geographic transformation.

Title: Using the ENVI Map Projection Engine Logging Feature
Description: The purpose of this logging feature is to enable the debugging of map projection issues.

Title: Creating ENVI Map Projection Engine User Defined Objects
Description: Creating user defined datums, geogcs's, geogtrans, projcs's and spheroids.

Title: Defining ENVI Map Projection Engine Datum Overrides
Description: How to override a datum. (Requires ENVI 4.7 SP1 or later version)

ENVI 5

Title: Defining ENVI Map Projection Engine Geographic Transform Overrides
Description: How to override the default geographic transformation.

Title: Using the ENVI Map Projection Engine Logging Feature
Description: The purpose of this logging feature is to enable the debugging of map projection issues.

Title: Creating ENVI Map Projection Engine User Defined Objects
Description: Creating user defined datums, geogcs's, geogtrans, projcs's and spheroids.

Title: Defining ENVI Map Projection Engine Datum Overrides
Description: How to override a datum.

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ENVI Map Projection Engine Reference Files

Note: ENVI switched from using version 9.3 of the ESRI Projection Engine with ENVI 4.7 and 4.8, to using version 10 with ENVI 5.  Therefore, the files describing supported projection types, datums, etc. are different for ENVI 4.7 and 4.8 than for ENVI 5.


ENVI 4.7 and 4.8

EnviPEDatums.txt
- contains a list of predefined datum constants.
- contains a list of predefined datum strings.

EnviPeGeogcs.txt
- contains a list of geogrpahic coordinate systems (Geogcs) constants.
- contains a list of geogrpahic coordinate systems (Geogcs) strings.

EnviPEGeographicTransformMethods.txt
- contains a list of predefined geographic transformation method constants.
- contains a list of predefined geographic transformation method strings.

EnviPEGeographicTransforms.txt
- contains a list of predefined geographic transform constants.
- contains a list of predefined geographic transform strings.
- this list can be referenced when defining a geographic transform override.

EnviPEParameters.txt
- contains a list of the projection parameter constants.
- contains a list of the projection parameter strings.

EnviPEProjcsStrings.txt
- contains a list of predefined projected coordinate systems (Projcs) codes/strings sorted by type.

EnviPEProjectionTypes.txt
- contains a list of the projection type constants.
- contains a list of the projection type strings.

EnviPESpheroids.txt
- contains a list of predefined spheroid constants.
- contains a list of predefined spheroid strings.

EnviPEPrimeMeridians.txt
- contains a list of predefined prime meridians constants.
- contains a list of predefined prime meridians strings.

EnviPEUnits.txt
- contains a list of predefined units constants.
- contains a list of predefined units strings.

ENVI 5

EnviPEDatums.txt
- contains a list of predefined datum constants.
- contains a list of predefined datum strings.

EnviPeGeogcs.txt
- contains a list of geograpahic coordinate systems (Geogcs) constants.
- contains a list of geograpahic coordinate systems (Geogcs) strings.

EnviPEGeographicTransformMethods.txt
- contains a list of predefined geographic transformation method constants.
- contains a list of predefined geographic transformation method strings.

EnviPEGeographicTransforms.txt
- contains a list of predefined geographic transform constants.
- contains a list of predefined geographic transform strings.
- this list can be referenced when defining a geographic transform override.

EnviPEParameters_v10.txt
- contains a list of the projection parameter constants.
- contains a list of the projection parameter strings.

EnviPEProjcsStrings.txt
- contains a list of predefined projected coordinate systems (Projcs) codes/strings sorted by type.

EnviPEProjectionTypes.txt
- contains a list of the projection type constants.
- contains a list of the projection type strings.

EnviPESpheroids.txt
- contains a list of predefined spheroid constants.
- contains a list of predefined spheroid strings.

EnviPEPrimeMeridians.txt
- contains a list of predefined prime meridians constants.
- contains a list of predefined prime meridians strings.

EnviPEUnits.txt
- contains a list of predefined units constants.
- contains a list of predefined units strings.