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.