Routines (alphabetical) > Routines: M > MAP_PROJ_INVERSE

# MAP_PROJ_INVERSE

The MAP_PROJ_INVERSE function transforms map coordinates from Cartesian (x, y) coordinates to longitude and latitude, using either the !MAP system variable or a supplied map projection variable created by MAP_PROJ_INIT.

## Syntax

Result = MAP_PROJ_INVERSE (X [, Y] [, MAP_STRUCTURE=value] [, /RADIANS] )

## Return Value

The result is a (2, n) array containing the longitude/latitude coordinates.

## Arguments

### X

An n-element vector containing the x values. If the Y argument is omitted, X must be a (2, n) array of X and Y pairs.

### Y

An n-element vector containing y values. If this argument is omitted, X must be a (2, n) array of X and Y pairs.

## Keywords

### MAP_STRUCTURE

Set this keyword to a !MAP structure variable containing the projection parameters, as constructed by the MAP_PROJ_INIT. If this keyword is omitted, the !MAP system variable is used.

### RADIANS

Set this keyword to indicate that the returned longitude and latitude coordinates should be expressed in radians. By default, returned coordinates are expressed in degrees.

### Thread Pool Keywords

This routine is written to make use of IDL’s thread pool, which can increase execution speed on systems with multiple CPUs. The values stored in the !CPU system variable control whether IDL uses the thread pool for a given computation. In addition, you can use the thread pool keywords TPOOL_MAX_ELTS, TPOOL_MIN_ELTS, and TPOOL_NOTHREAD to override the defaults established by !CPU for a single invocation of this routine. See Thread Pool Keywords for details.

## Version History

5.6 | Introduced
6.2 | Thread pool keywords added

## See Also

MAP_PROJ_FORWARD, MAP_PROJ_INIT, The IDL Thread Pool, Thread Pool Keywords