How to get GTOPO30 or Hydro1k dem data into ArcGIS/ArcView

by J Ramón Arrowsmith, July 28, 2003; updated November 19, 2003; July 17, 2006.

Get the data

Hydro 1k seems to be slightly higher quality and the same resolution, and it is available continent by continent (it is also hydrologically corrected):
http://edcdaac.usgs.gov/gtopo30/hydro/index.html

Un tar and unzip it

on Unix:
tar xvf as_dem.tar
gunzip as_dem.bil.gz (the main image file needs to be unzipped

Make the image an appropriate GRID

"Users of ARC/INFO or ArcView can display the DEM data directly after simply renaming the file extension from .DEM 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. 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"
--from http://edcdaac.usgs.gov/gtopo30/README.html

So, using Arc (on unix or command line in ArcWorkstation on Windows)

Arc: imagegrid as_dem.bil as_dem
This won't work if you don't put at least the .hdr in with the .bil (doesn't happen automatically when you unzip the files.
Arc: rename as_dem in_grid (probably not necessary)
Importantly, go to grid (just type grid in arc):
Grid: out_grid = con(in_grid >= 32768, in_grid - 65536, in_grid)
Grid: rename out_grid as_demclean (again this rename is probably not necessary, but I did it to get the above grid math exactly correct)

Here is a good explanation for how to do this in ArcGIS Desktop

http://www-sul.stanford.edu/depts/gis/DEM_SDTS.html--as noted above, make sure that you get the *.hdr, etc. in with the .bil file so Arc can find it.

ArcView Instructions (untested)--Require Image Analyst; I don't know how to do this in ArcToolBox

"The ArcView procedures are as follows: Note: HYDRO1K or GTOPO30 can be viewed in ArcView as an image but no geo-processing can be accomplished until the ArcView Spatial Analyst Extension (raster module) has been purchased. This extension must be loaded (turned on) for steps four through six. To receive correct projected coordinates in ArcView or ArcMap the bil needs to be ingested with the a properly formatted header and world file. The associated world and header file reference the upper left image corner coordinates and output pixel size (horizontal grid spacing). Examples of the properly formated ESRI header and world file can be found at http://edcdaac.usgs.gov/gtopo30/README.html The steps are as follows: 1) Rename dem.dem to dem.bil 2) Under the View Pull down, Click the Add Theme Button 3) Click Add Image Data Source, Pick the GTOPO30 image (.bil file) 4) Under the Theme Pull down, Click the Convert to Grid Button 5) Under the Analysis Pull down, Click Map Calculator - Type in the following formula: Syntax: ([NwGrd1] >= 32768.AsGrid).Con ([NwGrd1] - 65536.AsGrid, [NwGrd1]) 6) Under the Theme Pull down, Click the Save Data Set Button, Save Map Calculator Theme",br>--from: http://edcdaac2.usgs.gov/custhelp/product_info.asp?p_refno=011231-000000

Getting it to display and be properly manipulated in ArcMap

You need to specify the projection. Look in the readme that comes with the continent. For Asia, it says (among other things):

The Asian HYDRO1k data set is made up of six raster and
two vector layers.  The projection and georeferencing information
for the Asian data set include:

Number of rows = 11882
Number of columns = 9341

XY corner coordinates (edge of pixel):

   Lower left:   -4355500.000, -5438500.000
   Upper left:   -4355500.000,  6443500.000
   Upper right:   4985500.000,  6443500.000
   Lower right:   4985500.000, -5438500.000

Projection used:  Lambert Azimuthal Equal Area
                  Units = meters
                  Pixel Size = 1000 meters
                  Radius of Sphere of Influence = 6,370,997 meters
                  Longitude of Origin = 100 00 00E
                  Latitude of Origin = 45 00 00N
                  False Easting = 0.0
                  False Northing = 0.0

So, one needs to go into ArcCatalogue, find the grid file, and right click to find the properties. For the Spatial reference, you shoud interactively define it with the above data. The one thing I was unsure of is the datum. I used the WGS84 Spheroid which is the datum for GTOPO30 and so maybe that is ok?

One other issue that came up is that sometimes we could not get the Raster Calculator for example to operate on the originally converted file and so Lela Prashad came up with this fix:

I think I fixed your problem but I don't know if I can tell you why this
works. In ArcMap, I opened the raster calculator and clicked on na_dem. Then I
hit evaluate. So it just re-evaluated the original grid. I was then able to
put the heat flow points on top and calculate zonal statistics for those
points in map calculator. I could not do that with the original na_dem.

I put the re-calculated na_dem grid in the same folder and called it
recal_na_dem