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SRTM data and ArcGIS (ArcView)   Andrea Cattarossi Feb 14, 2002
Re: SRTM data and ArcGIS (ArcView)   C P Feb 14, 2002
Re: SRTM data and ArcGIS (ArcView)   Andrea Cattarossi Feb 15, 2002
Re: SRTM data and ArcGIS (ArcView)   Philip Harreld Feb 26, 2002
Re: SRTM data and ArcGIS (ArcView)   Debbie Donahue Jun 04, 2002
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Subject SRTM data and ArcGIS (ArcView) 
Author Andrea Cattarossi 
Date Feb 14, 2002 
Message I am following the story with the new SRTM data from NIMA. In the USGS FTP site I had the chance to download some file now available. A note explains that I can see this raster data in Arcview simply changing the file extension from *.hgt to *.bil. I did it but it wont work. Anybady had any luck with these kind of data and Arcview? Anybody found a way to read the x,y,z data even without ArcInfo and IMAGEGRID?

Thanks for any help

Andrea 
   
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Subject Re: SRTM data and ArcGIS (ArcView) 
Author C P 
Date Feb 14, 2002 
Message have you tried going into the tool drop down menu then options then raster---toggle the radio buttons in the raster format browsing 1 or two times. This most of the times will make it appear the next time you add data. First of all do you have the box checked in that area to view.bil files?
Cameron 
   
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Subject Re: SRTM data and ArcGIS (ArcView) 
Author Andrea Cattarossi 
Date Feb 15, 2002 
Message I tried... but I get a message "Invalid raster dataset. Failed to create raster layer".
I also tried with ArcView 3.2 and the problem seems to be related to the absence of a heather line on the file. The suggestion is to have an ASCII file describing which kind of file I am trying to open... but I am not sure how to do it or if this is really the solution.

In the USGS note, posted on the SRTM FTP site for ARC/INFO users, they say that I can read the see the raster with ArcView (but I cannot edit it).

Andrea
 
   
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Subject Re: SRTM data and ArcGIS (ArcView) 
Author Philip Harreld 
Date Feb 26, 2002 
Message The note you refer to is a bit misleading, because even though the format of the SRTM .hgt files is band interleaved by line (BIL), they still need an associated header file before ArcMAP can recognize them. The header file is a file with the same name as the .bil file, but with a .hdr extension. It is an ASCII file (i.e., use Notepad to edit it), and it contains the information that ArcMAP needs to understand the specific contents of the .bil file.

The note correctly identifies the fields required for the 3 arc-second SRTM file N37W105.bil, and those fields are:

BYTEORDER M (for big-endian byte order in the file)
LAYOUT BIL (for band interleaved by line format)
NROWS 1201 (for 1201 rows in the raster)
NCOLS 1201 (for 1201 columns in the raster)
NBANDS 1 (for a single band in the file)
NBITS 16 (for the number of bits for each cell)
BANDROWBYTES 2402 (number of bytes in each row of the band)
TOTALROWBYTES 2402 (total bytes in each row)
BANDGAPBYTES 0 (for no gaps between the bands in the file)
NODATA -32768 (for the NoData value)
ULXMAP -104.99958333333334 (for the x coordinate (in decimal degrees) of the center of the cell in the upper left corner of the raster)
ULYMAP 38.00041666666667 (for the y coordinate (in decimal degrees) of the center of the cell in the upper left corner of the raster)
XDIM 0.000833333333333 (for the x difference (in decimal degrees) between cell centers)(at 3 arc-seconds)
and
YDIM 0.000833333333333 (for the y difference (in decimal degrees) between cell centers)(at 3 arc-seconds)

Each field name (i.e., BYTEORDER) and its corresponding value (i.e., M) appears on a single line in the .hdr file, and the field name and value are separated by spaces.

Once you build a header file (.hdr) to go along with your downloaded .hgt (.bil) file, ArcMAP will read it in just fine. The note is correct when it says that you can't edit the file unless you convert it to a GRID file first.

Hope this helps!

Phil 
   
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Subject Re: SRTM data and ArcGIS (ArcView) 
Author Debbie Donahue 
Date Jun 04, 2002 
Message I've been asked to enter SRTM data into ArcGIS 8. I found your very helpful msg dated Feb 26,2002 on creating the .hdr file. However I have 2 followup questions: 1) I understand how you got a value for ULXMAP - by subtracting 1/2 * XDIM from 105 (105 taken from the 3 arc-sec file name N37W105.bil.) However I do not understand how you got a value of 38.00041666... for ULYMAP, since 37 - (1/2 * YDIM) or 37 + (1/2 * YDIM) does not = 38.00041666....
2) I thought .000833333333333 equaled 1/2 the cell size, not the difference between cell centers. Can you tell me how you determined this?

Thanks for contributions to this!
Debbie