ArcGIS 10 Problems creating Hillshade from DEM

[Anonymous User]

Original User: fbelanger7

I have a DEM which has several tiles to cover several hundred square kilometers. I have used a mosaic dataset to mosaic the whole DEM and now I would like to create an hillshade but if I use the hillshade function I get display problem (some parts appear as if they were integer datas instead of floating points) and if I use 3D analyst to geoprocess the whole mosaic I get white lines in it and a part of the data missing. Does anybody has an idea of what is wrong? See attached images for more details.

Thank you,
Francis Bélanger

[JakubSisak]

fbelanger7;237351now I would like to create an hillshade but if I use the hillshade function I get display problem (some parts appear as if they were integer datas instead of floating points)[/QUOTE wrote:

Hello there,
Can you confirm that when you run this particular area without mosiacing it first that it in fact appears correct?  Any chance the source data is Canadian DEM obtained from Geobase or NRC?

[Anonymous User]

Original User: timmo1982

One often gets these types of problems when combining DEM data, especially where it the source data is sparse (i.e. contour information on flat-land) and the terrain is interpolated (i.e. using TopoToRaster).

If you are simply merging existing data, then that makes things harder. If you are creating the DEM information yourself (i.e. from vector data, contours or points), then create tiles that have large amounts of overlap (i.e. by buffering existing tiles) then re-make the DEM tiles and when merging them into the final large tile, set the overlap rule to 'average'. This should smooth out any differences in the areas where DEM interpolation doesn't have much info to work on and is 'guessing' more.

[FrancisBélanger]

Sorry for the replying delay.

Actually the DEM seems to be right before creating the mosaic dataset. The when I create the mosaic dataset aformentioned problems happen. The DEM I'm using was produced from LIDAR datas and not from NRC.

Francis Bélanger

[Anonymous User]

Original User: mboeringa2010

I don't know if this is in any way related to your issues, but I have seen issues with ArcGIS 10.0's (SP5) hillshading too.

In my case, display issues arise when I use the dynamic "Use hillshade effect" checkbox in a raster DEM layer's properties under the "Symbology" tab.

The problem I witness, and that I still haven't figured out what causes it beside some bug in ArcGIS 10 display engine, is that somewhere half way down the ArcMap Dataframe display, the hillshading effect stops being displayed and the DEM turns into its ordinary "flat" display. In the attached image you can see this. Please note the exact location where this happens is NOT fixed, if I pan the frame, the horizontal border shifts to another Y location in the dataframes coordinate system, and is also not fixed on the screens height. It seems rather random.

The usage of this particular DEM has proven stable in any other respect, no issues or crashes, just this display issue. I haven't had time to report this to ESRI yet, nor time to really make sure it isn't some weird raster data set issue. I have, however, imported the data into a file geodatabase and that still gave the same issues.

For my purpose, I solved the issue by calculating a separate hillshade layer using the Spatial Analyst tools and adding this to dataframe. By setting a transparency on the DEM, I can get an acceptable "hillshade" type display without the same issues arising as in the dynamic hillshading effect of the layer properties.

Marco

[FrancisBélanger]

After more investigations I have found that the problem seems to come from the overviews. The original image was OK but when I zoom out the overview shows and it looks like the values of some raster dataset don't have decimal values.

Francis Bélanger