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Technical Article   HowTo:  Convert GTOPO30 DEM data to a grid using ArcGIS

Article ID: 22749
Software:  ArcGIS - ArcEditor 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1 ArcGIS - ArcInfo 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1 ArcGIS - ArcView 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1
Platforms: N/A

Summary

You can use ArcGIS Spatial Analyst to convert a United States Geological Survey (USGS) GTOPO30 digital elevation model (DEM) to an ESRI grid format.

Click the USGS GTOPO30 link in the Related Information section to download a GTOPO30 DEM. This file comes as a .tar file, which contains the *.dem and *.hdr files. Both files are required for this operation.

Procedure

  1. Uncompress the TAR file using WinZip 6.2 or higher.-show me-
    Summary
    Instructions provided describe how to fix WinZip configuration and avoid data corruption. Data may be corrupted if the data is extracted with the WinZip utility. The corruption which occurs can affect any kind of GIS data.

    The steps in this article apply to all versions of WinZip.
    Procedure
    A default setting must be changed on the WinZip compression utility. The default setting may corrupt data while data is being unzipped.

     This checkbox has no effect on data when the data is zipped.

    Follow the steps below.

    1. Open WinZip Classic.
    2. Select Options > Configuration > Miscellaneous tab.
    3. Uncheck the 'TAR file smart CR/LF conversion' box. The box will remain unchecked until you check it again.
    4. Unzip and import the data.

       Here are some of the error messages and problems which can occur if the 'TAR file smart CR/LF conversion' is checked when data is extracted.
      -show me-

    5. Extra steps are necessary if the compressed file has a .TAR.GZ extension from compression on Unix. Follow the instructions below to avoid corrupting these data.

      A. When the .tar.gz file is double-clicked to open, WinZip will open a dialog saying

      "Archive contains X number of files.
      <file_name(s).tar>
      'Should WinZip decompress it to temporary folder and open it?'

      Click NO.

      B. Check the 'TAR file smart CR/LF conversion' box. Extract the .tar file from the .gz archive to the desired folder.

      C. Double-click on the .tar file to start WinZip a second time. Uncheck the 'TAR file smart CR/LF conversion' box, and extract the .tar file.


     If not properly configured WinZip can corrupt the files.

  2. Change the *.dem extension to *.bil.
  3. Open ArcCatalog.
  4. Navigate to the *.bil created in Step 2.
  5. Right-click on the *.bil, click Export, and click the Raster to Different Format option. Specify the location to which you will save the new grid, and ensure the Save As Type is set to ESRI GRID.
  6. Open ArcMap and add the grid created in Step 5.
  7. On the ArcGIS Spatial Analyst toolbar, click Spatial Analyst and select Options.
  8. Click the General tab and set the working directory.
  9. Click the Extent tab and set the analysis extents to Same as layer 'your grid'.
  10. Click the Cell Size tab and set the cell size to Same as layer 'your grid'. Click OK.
  11. Navigate to ArcGIS Spatial Analyst and select the Raster Calculator. Enter the following expression, substituting your grid for [in_grid]. Include the square brackets.

    CON([in_grid] >= 32768,[in_grid] - 65536,[in_grid])

    Click Evaluate.
  12. The ocean areas (-9999) can be converted to NODATA using the SETNULL function. Insert the Calculation from Step 11 for [Calculation]. Include the square brackets.

    setnull([Calculation ] == -9999, [Calculation ])

    Click Evaluate.
  13. Save the final output to disk by right-clicking the Calculation result from Step 12 and selecting Make Permanent.

Related Information

  • Convert GTOPO30 DEM data into a grid using ArcINFO GRID
    Instructions provided describe how to convert GTOPO30 DEM data into a grid. Use ArcInfo GRID to convert a USGS GTOPO30 DEM to grid format while retaining the digital elevation data values. Click the link in the Related Information section to do...
  • UGSG GTOPO30
  • Convert GTOPO30 DEM data into a grid
    You can use ArcView Spatial Analyst to convert a USGS GTOPO30 DEM to grid format while retaining the digital elevation data values. Click the link in the Related Information section to download a GTOPO30 DEM. This file comes as a .TAR file, whi...

Created: 6/19/2002
Last Modified: 11/15/2006

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Comments

By Anonymous - 02/24/2004 10:22 AM

I have ArcGIS 8.3 (just got it) and your step 5)Right-click on the *.bil, click Export, and click the Raster to Different Format option. Specify the location to which you will save the new grid, and ensure the Save As Type is set to ESRI GRID. When I right click the only option available is to change to MRSid format!