Hi Brendan, If you're using ER Mapper, then simply follow the instructions below (from the srtm website) to create a bil/hdr pair. The hgt is simply a 16-bit bil file.
----------------------------------- Rename the file extension from .HGT to .BIL. Then create a .HDR file as below. The contents of a sample file that works with 3 arc-second SRTM file N37W105.hgt are: -------------------------------------------------------------------------- BYTEORDER M LAYOUT BIL NROWS 1201 NCOLS 1201 NBANDS 1 NBITS 16 BANDROWBYTES 2402 TOTALROWBYTES 2402 BANDGAPBYTES 0 NODATA -32768 ULXMAP -104.99958333333334 ULYMAP 38.00041666666667 XDIM 0.000833333333333 YDIM 0.000833333333333 -------------------------------------------------------------------------- Best Regards, Martin Higham Avantra Geosystems ph (61 3) 8504 0428 0425-730-428 fx (61 3) 9596 7997 www.avantra.com.au > -----Original Message----- > From: Brendan.O'[EMAIL PROTECTED] > [mailto:Brendan.O'[EMAIL PROTECTED] > Sent: Thursday, 17 June 2004 23:26 > To: [EMAIL PROTECTED] > Subject: MI-L SRTM hgt How ? > > > > > > > Hello, > > Regarding the recently oft-mentioned SRTM DEMs, I note Ihab Hawater has > kindly pointed to the availability of 'Grid Translator Pro > for MapInfo Vertical Mapper' > > Must one have Vertical Mapper in order to allow 'Grid Translator Pro > for MapInfo Vertical Mapper' translate to other formats? > > I have at my disposal MapInfo with Encom's Discover and separately ER > Mapper and Geosoft Oasis Montaj. Are there alternative routes to the SRTM > *.hgt files open to me? > > Thanks > > Brendan O'Donovan > > > --------------------------------------------------------------------- > List hosting provided by Directions Magazine | www.directionsmag.com | > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > Message number: 12254 >
Users of ARC/INFO or ArcView can display the DEM data directly after renaming the file extension from .HGT to .BIL. However, if a user needs access to the actual elevation values for analysis in ARC/INFO the DEM must be converted to an ARC/INFO grid with the command IMAGEGRID. For IMAGEGRID to work there must be a separate header file whose name (including case) is exactly the same as the image file name. The contents of a sample file that works with 3 arc-second SRTM file N37W105.hgt are below -------------------------------------------------------------------------- BYTEORDER M LAYOUT BIL NROWS 1201 NCOLS 1201 NBANDS 1 NBITS 16 BANDROWBYTES 2402 TOTALROWBYTES 2402 BANDGAPBYTES 0 NODATA -32768 ULXMAP -104.99958333333334 ULYMAP 38.00041666666667 XDIM 0.000833333333333 YDIM 0.000833333333333 -------------------------------------------------------------------------- IMAGEGRID does not support conversion of signed image data, therefore the negative 16-bit DEM values will not be interpreted correctly. After running IMAGEGRID, an easy fix can be accomplished using the following formula in Grid: out_grid = con(in_grid >= 32768, in_grid - 65536, in_grid) The converted grid will then have the negative values properly represented, and the statistics of the grid should match those listed in the .ANN file. In addition, below are the contents of an AML script that documents the process of converting two elevation files into DEMs, mosaicks the two grids, projects to UTM13, and creates a hillshade grid for display with ArcMap, ArcPlot, or ArcView. -------------------------------------------------------------------------- /* SRTM.AML /* AML for converting SRTM image files in grids and hillshades. /* Rename image file to be lower case and have .bil extension. /* Create and check header file. Merged DEMs correspond to the La Junta /* 250K sheet. /* &IF [EXISTS n37w104raw -GRID] &THEN KILL n37w104raw ALL &IF [EXISTS n37w105raw -GRID] &THEN KILL n37w105raw ALL imagegrid n37w104.bil n37w104raw imagegrid n37w105.bil n37w105raw /* GRID DISPLAY 9999 &IF [EXISTS n37w104dd -GRID] &THEN KILL n37w104dd ALL &IF [EXISTS n37w105dd -GRID] &THEN KILL n37w105dd ALL n37w104dd = con(n37w104raw >= 32768, n37w104raw - 65536, n37w104raw) n37w105dd = con(n37w105raw >= 32768, n37w105raw - 65536, n37w105raw) &IF [EXISTS lajdd -GRID] &THEN KILL lajdd ALL &IF [EXISTS laj13 -GRID] &THEN KILL laj13 ALL &IF [EXISTS lajhill13 -GRID] &THEN KILL lajhill13 ALL lajdd = merge(n37w104dd, n37w105dd) laj13 = project(lajdd, ddutm13.prj, bilinear) lajhill13 = hillshade(laj13, 315., 45., shade) MAPE lajhill13 GRIDP lajhill13 # EQUALAREA # GRAY &PAUSE QUIT /* &RETURN -------------------------------------------------------------------------- Many thanks and congratulations to to Arthur Tarr of the U.S. Geological Survey in Denver for figuring out the SRTM format and generating the sample header file and script above.
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