HDR and STX files

The formats of the header (HDR) and statistics (STX) files for SRTM-3 data are given below.

HDR file

The header file is a text file with the extension HDR. The contents of the file (for 3 arc-sec data) is:

BYTEORDER M
LAYOUT BIL
NROWS 1201
NCOLS 1201
NBANDS 1
NBITS 16
BANDROWBYTES 2402
TOTALROWBYTES 2402
BANDGAPBYTES 0
NODATA -32768
ULXMAP 32.000000000000
ULYMAP 30.000000000000
XDIM 0.000833333333333
YDIM 0.000833333333333

Lines 11 and 12 specify the X-coordinate (ULXMAP) and Y-coordinate (ULYMAP) of the center of the grid cell in the upper left corner of the map. These are the only two lines you should change for each tile. Remember to use signed coordinates: positive for longitude E and latitude N, negative for longitude W and latitude S.

STX file

The statistics file is a one-line text file with the extension STX. The sample contents of the file is:

1 0 1000 500 100

The STX file consists of a “1”, followed by the minimum, maximum, mean, and standard deviation of the Z values. Surfer uses the minimum and maximum, so enter those values in the STX file if you know them. If you don't know the minimum and maximum, enter any reasonable values, and use Grid | Convert to convert to a GRD file. Surfer will calculate the correct Z minimum and maximum values and save them in the GRD file.

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