[Gdal-dev] SRTM data and GDAL

[Markus Neteler]

Dear GDAL users,

since yesterday a SRTM shuttle elevation data are available
for Northern America at around 90m resolution (0:00:03 deg):

http://www.jpl.nasa.gov/srtm/cbanddataproducts.html
ftp://srtm.usgs.gov/pub/data/srtm/North_America/3arcsec/

The trick to use them with GDAL is as follows:

- unpack the .zip file
- mv NXXWYYY.hgt NXXWYYY.bil
- create a .hdr file (ARC/INFO style) from the file name:

Example for N18W077.bil

BYTEORDER     M
LAYOUT        BIL
NROWS         1201
NCOLS         1201
NBANDS        1
NBITS         16
BANDROWBYTES  2402
TOTALROWBYTES 2402
BANDGAPBYTES  0
NODATA        -32768
ULXMAP        -76.9995833333        <- WYYY - 0.0004166667
ULYMAP        19.00041666666667     <- NXX  + 1.0004166667
XDIM          0.000833333333333
YDIM          0.000833333333333


Then gdalinfo then accepts the file and reports:

gdalinfo -mm N18W077.bil
Driver: EHdr/ESRI .hdr Labelled
Size is 1201, 1201
Coordinate System is '
Origin = (-77.000000,19.000833)
Pixel Size = (0.000833,-0.000833)
Corner Coordinates:
Upper Left  ( -77.0000000,  19.0008333)
Lower Left  ( -77.0000000,  18.0000000)
Upper Right ( -75.9991667,  19.0008333)
Lower Right ( -75.9991667,  18.0000000)
Center      ( -76.4995833,  18.5004167)
Band 1 Block=1201x1 Type=Int16, ColorInterp=Undefined
    Computed Min/Max=-10.000,2024.000
  NoData Value=-32768

Maybe the GDAL authors could add a simple HGT driver which
automagically constructs the .hdr file internally on the fly.

Anyway, with above method you can easily import/convert
the data (also tested with GRASS).

Cheers

 Markus

-- 
Markus Neteler

ITC-irst, Istituto per la Ricerca Scientifica e Tecnologica
      Project on Predictive Models for the Environment    
Via Sommarive, 18        -       38050 Povo (Trento), Italy
tel +39 0461 314 520 (fax -591)           http://mpa.itc.it