[visit-users] DEM display

Brad Whitlock whitlock2 at llnl.gov
Wed Mar 3 12:58:07 EST 2010

Hi Dianne,
    Yes, you can send me an example file. It would be good to have 
when I'm able to try adding support for "no data" values in the GDAL 


>I have had some similar problems displaying .asc files.  Adding a 
>threshold operator helps, but the nodata values seem to be assigned 
>a value close to the minimum of the dataset.  If I set the minimum 
>threshold to the minimum value in the legend, I am able to get rid 
>of the nodata values, but I also lose some of the values from my 
>.asc file that have a value equal to the minimum. Can I send you and 
>Brad Whitlock whitlock2 at llnl.gov
>Tue Feb 16 13:24:23 EST 2010
>VisIt's GDAL plugin is not currently set up to remove portions of the
>data using "nodata" values. This probably is not too difficult to
>correct since it looks like the "nodata" value can be queried from
>Since the nodata values are not currently removed, adding a Threshold
>operator is a good workaround. The Pseudocolor plot will need its
>limits set relative to the "current plot" instead of the "original
>data" for the legend to exclude the nodata values.
>As for the Z-axis values, which mesh are you visualizing? The GDAL
>plugin provides both flat and elevated versions of the mesh. As
>written, the "elevated" version of the mesh provided by the GDAL
>reader uses the Z values from the file. If your height units are not
>the same as the x/y units then a Transform operator may be needed to
>bring the plot into a 1:1 aspect ratio with height vs width.
>If you're using the flat mesh with the Elevate operator, you'll get a
>plot where the vertical values appear to be normalized into [0,1] so
>the data can be plotted in roughly a cube shape. The Z-axis would
>then be labeled with values in [0,1]. Is this the 0 that you're
>talking about?
>On Mon, 2010-02-15 at 21:38 -0600, Brian Clark wrote:
>>  Hi,
>>  I have a DEM formatted file with nodata values (-9999) in portions of
>>  the area. When viewing in VisIt, the nodata values show, even if a
>>  threshold is set (though normally, the nodata areas seem to inherit the
>>  same value and the lowest value in the DEM). What am I doing wrong? Is
>>  there a nodata option to specify for these DEM's related to the GDAL plugin?
>>  Also the DEM contains negative values that show up in the color legend,
>>  but the Z axis appears to cut everything off below zero? Is it possible
>>  to show the full scale of DEM values (those below zero)?
>>  thanks,
>>  brc
>>  --
>Dianne L. Brien, Hydrologist
>U.S. Geological Survey, Landslide Hazards
>345 Middlefield Road, MS 910
>Menlo Park, CA 94025
>dbrien at usgs.gov
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Brad Whitlock                   Lawrence Livermore National Laboratory
whitlock2 at llnl.gov
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