Why do GeoTIFF images display incorrectly in some GIS applications?

GeoTIFF images in Indiana state plane map projections may not display correctly in some applications due to differences in linear units specified in EPSG codes.

The International Association of Oil & Gas Producers (OGP) Surveying and Positioning Committee maintains and publishes the EPSG Geodetic Parameter Dataset. The OGP recognizes the following codes as valid Indiana EPSG codes used by local and state governments:

• 2965 ( NAD_1983_StatePlane_Indiana_East_FIPS_1301_Feet )
• 2966 ( NAD_1983_StatePlane_Indiana_West_FIPS_1302_Feet )

The above codes specify the linear unit in feet. Current GeoTIFF specifications use EPSG codes that specify the linear unit in meters:

• 26973 ( NAD_1983_StatePlane_Indiana_East_FIPS_1301 )
• 26974 ( NAD_1983_StatePlane_Indiana_West_FIPS_1302 )

Applications created by vendors such as ERDAS and ESRI use two GeoTIFF metadata keys, ProjectedCSTypeGeoKey and ProjLinearUnitsGeoKey, to define Indiana state plane projections using feet, for example:

The EPSG code for PCS_NAD83_Indiana_East is 26973, which defines the linear unit in meters. This practice violates the GeoTIFF specifications by overwriting the linear units defined by ProjectedCSTypeGeoKey with different units defined by the ProjLinearUnitsGeoKey. Some software applications that follow a strict interpretation of the GeoTIFF specifications cannot read the value of the ProjLinearUnitsGeoKey; instead, they display the image using the linear unit of meters. Some reader software can recognize the problem and apply the appropriate override.

UITS requested that future software versions use the newer 2965 and 2966 EPSG codes as the value for ProjectedCSTypeGeoKey. ERDAS staff are reviewing this request and researching other solutions.

Multiple free GIS applications, as well as proprietary applications, are available for viewing geospatial data. If imagery such as the IndianaMap 2005 GeoTIFFs do not display correctly in an application, consider using a different application.

Additionally, you can modify an image's GeoTIFF metadata tags using the GDAL utilities' GDAL_TRANSLATE application to set the GeoTIFF ProjectedCSTypeGeoKey to 2965 or 2966. The DOS program listgeo will report GeoTIFF metadata tags to either the screen or an output text file.

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