This procedure builds a GLT file for the corresponding x and y map location images. These and the associated map projection are used to build the GLT file in the specified output projection. You can also specify a rotation for the output GLT image. GLT images are then used to georeference additional images.

Syntax

ENVI_DOIT, 'ENVI_GLT_DOIT', DIMS=array, I_PROJ=structure, /IN_MEMORY, O_PROJ=structure, OUT_NAME=string, PIXEL_SIZE=value [, R_FID=file ID] [, ROTATION=value] [, /SUPER] , X_FID=file ID, X_POS=array, Y_FID=file ID, Y_POS=array

Keywords

DIMS

The “dimensions” keyword is a five-element array of long integers that defines the spatial subset (of a file or array) to use for processing. Nearly every time you specify the keyword FID, you must also specify the spatial subset of the corresponding file (even if the entire file, with no spatial subsetting, is to be processed).

  • DIMS[0]: A pointer to an open ROI; use only in cases where ROIs define the spatial subset. Otherwise, set to -1L.
  • DIMS[1]: The starting sample number. The first x pixel is 0.
  • DIMS[2]: The ending sample number
  • DIMS[3]: The starting line number. The first y pixel is 0.
  • DIMS[4]: The ending line number

To process an entire file (with no spatial subsetting), define DIMS as shown in the following code example. This example assumes you have already opened a file using ENVI_SELECT or ENVI_PICKFILE:

  envi_file_query, fid, dims=dims

I_PROJ

Use this keyword to specify the input projection for the x and y map location images. Both x and y must be in the same projection. You cannot set I_PROJ to the Arbitrary projection. I_PROJ is a projection structure returned from ENVI_PROJ_CREATE or ENVI_GET_PROJECTION.

IN_MEMORY

Set this keyword to specify that output should be stored in memory. If you do not set IN_MEMORY, output will be stored on disk and you must specify OUT_NAME (see below).

O_PROJ

Use this keyword to specify the output projection for the GLT file. You cannot set O_PROJ to the Arbitrary projection. O_PROJ is a projection structure returned from ENVI_PROJ_CREATE or ENVI_GET_PROJECTION.

OUT_NAME

Use this keyword to specify a string with the output filename for the resulting data. If you set the keyword IN_MEMORY, you do not need to specify OUT_NAME.

PIXEL_SIZE

Set this keyword to a scalar value that represents both the x and y pixel size of the output GLT image. Set these individually to this scalar value. The default value is calculated from the pixel size of the input projection.

R_FID (optional) 

ENVI Classic library routines that result in new images also have an R_FID, or “returned FID.” This is simply a named variable containing the file ID to access the processed data. Specifying this keyword saves you the step of opening the new file from disk.

ROTATION (optional)

Use this keyword to specify the rotation of the GLT image in the defined output projection. Rotation is expressed in degrees clockwise from north. The default is to calculate the rotation of the input x and y map location images. To set the GLT output image to north up, specify ROTATION=0.

SUPER (optional)

Set this keyword to output a super GLT file. If you set this keyword, then you must specify OUT_NAME, in which case the keyword IN_MEMORY is ignored.

X_FID

Use this keyword to specify the file ID for the x map projection values file. This value is returned from the keyword R_FID in the ENVI_OPEN_FILE procedure. X_FID is a long integer with a value greater than 0. An invalid file ID has a value of -1.

X_POS

Use this keyword to specify the band position of the x map projection values. X_POS is an array of long integers, ranging from 0 to the number of bands minus 1.

Y_FID

Use this keyword to specify the file ID for the y map projection values file. This value is returned from the keyword R_FID in the ENVI_OPEN_FILE procedure. Y_FID is a long integer with a value greater than 0. An invalid file ID has a value of -1.

Y_POS

Use this keyword to specify the band position of the y map projection values. Y_POS is an array of long integers, ranging from 0 to the number of bands minus 1.

API Version

4.2