Selecting Map Projection Types
Many functions require you to select an input and/or output map projection type for your data. Refer to the following procedure when projection selection is needed in any dialog.
- In the list of projection types, either:
- Click on the name of the projection to select it.
Different parameters are available depending on the selected projection type.
- Select the corresponding secondary parameters for the selected projection type:
- If you select Arbitrary, select either Pixel Based or Map Based by clicking on the arrow toggle button below the Units parameter.
Pixel-based uses the upper-left corner as the origin and map-based uses the lower left corner as the origin. Either selection only affects the y coordinates.
- To change the datum for a projection type, click Datum and select a datum from the list in the Select Geographic Datum dialog.
The datum conversions are done using the Molodensky Transformation (see the web page http://www.connect.net/jbanta/).
- If you select UTM, click the N or S toggle button to indicate if the selected latitude is north (N) or south (S) of the equator. Enter a zone, or click Set Zone and enter the latitude and longitude values to automatically calculate the zone.
- If you select a State Plane projection, enter the zone or click Set Zone and select the zone name from the list.
Both NOS and USGS zone numbers are shown next to the zone name.
- To designate the units for a projection type, click Units and select a unit type. Enter a pixel size (in the selected unit), if needed.
ENVI Online Help (August 12, 2005)