The ENVI_ENVISAT_GEOREF_DOIT procedure georeferences AATSR-, ASAR-, and MERIS-format Envisat data by extracting geolocation tie points from header information in the Envisat file.


ENVI_DOIT, 'ENVI_ENVISAT_GEOREF_DOIT' [, BACKGROUND=value] [, DEGREE=value] [, DIMS=array], F_FID=file ID [, GCP_NAME=string], /IN_MEMORY [, OUT_BNAME=string array], OUT_NAME=string [, OUT_PROJ=structure] [, POS=array] [, R_FID=variable] [, WARP_METHOD={0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8}] [, ZERO_EDGE=0]


BACKGROUND (optional)

Use this keyword to specify the value for all background pixels. The default value is 0.

DEGREE (optional)

Use this keyword to specify the degree of the polynomial warp when WARP_METHOD=3, 4, or 5. The default is DEGREE=1.

DIMS (optional)

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


Use this keyword to specify the file ID of the open file. This value is returned from the keyword R_FID in the ENVI_OPEN_FILE procedure. FID is a long integer with a value greater than 0. An invalid file ID has a value of -1.

GCP_NAME (optional)

Use this keyword to specify the name of the output file that contains the ground control ponts (GCPs). If you do not set this keyword, the points are not saved to disk.


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).

OUT_BNAME (optional)

Use this keyword to specify a string array of output band names.


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.

OUT_PROJ (optional)

Use this keyword to specify the projection of the resulting data. You cannot set OUT_PROJ to the Arbitrary projection. OUT_PROJ is a projection structure returned from ENVI_PROJ_CREATE or ENVI_GET_PROJECTION. The default projection is derived from the input data.

POS (optional)

Use this keyword to specify an array of band positions, indicating the band numbers on which to perform the operation. This keyword indicates the spectral subset of bands to use in processing. POS is an array of long integers, ranging from 0 to the number of bands minus 1. Specify bands starting with zero (Band 1=0, Band 2=1, etc.) For example, to process only Bands 3 and 4 of a multi-band file, POS=[2, 3].

POS is typically used with individual files. The example code below illustrates the use of POS for a single file with four bands of data:

envi_doit, 'envi_stats_doit', dims=dims, fid=fid, pos=pos, $
comp_flag=3, dmin=dmin, dmax=dmax, mean=mean, stdv=stdv, hist=hist

But what if you need to create an output file consisting of data from different bands, each from different files? Library routines such as CF_DOIT and ENVI_LAYER_STACKING_DOIT can accomplish this, but they use the POS keyword differently. Suppose you have four files, test1, test2, test3, and test4, with corresponding FIDs of fid1, fid2, fid3, and fid4, respectively. In the following example, you want Band 3 from test1 in the first position, Band 2 from test2 in the second position, Band 6 from test3 in the third position, and Band 4 from test4 in the fourth position. The code should be as follows:

  fid_array = [fid1,fid2,fid3,fid4]
envi_doit, 'cf_doit', dims=dims, fid=fid_array

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.

WARP_METHOD (optional)

Use this keyword to specify an integer value that indicates the combination of methods used to warp and resample the image.

  • 0: RST with nearest neighbor (default)
  • 1: RST with bilinear
  • 2: RST with cubic convolution
  • 3: Polynomial with nearest neighbor
  • 4: Polynomial with bilinear
  • 5: Polynomial with cubic convolution
  • 6: Triangulation with nearest neighbor
  • 7: Triangulation with bilinear
  • 8: Triangulation with cubic convolution

ZERO_EDGE (optional)

Set this keyword to specify that the edges outside of any triangles for the triangulation method are set to the value specified by the BACKGROUND keyword. The ZERO_EDGE keyword is only used when WARP_METHOD=6, 7, or 8.

Note: The ZERO_EDGE keyword is set by default. To disable this, explicitly set the ZERO_EDGE keyword to 0.

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