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Difference between hillshade and Image Analyst shaded relief in ArcMap10

January 06 2011 | 0 comments
Categories: Map Data, Symbology

Working on transition from 9.3.1 to 10 and am exploring hillshade and Image Analyst generated shaded relief differences. The IA generated shaded relief using a grayscale color ramp mimics a 3D/Spatial Analyst generated hillshade in appearance, but I'm wondering if they can be used interchangeably? The IA shaded relief is a 3 channel image even with the grayscale color ramp, unlike a 3D/Spatial Analyst generated hillshade. Wondering if you can point out any "issues" using an IA shaded relief as a 3D/Spatial Analyst hillshade. Realize that IA generated shaded relief is a temporary file and must be exported either from IA window or with right click on file in TOC. Losing the pull down hillshade (and others) shortcuts from the 3D and Spatial Analyst toolbars is the main driving force in exploring this.

Thanks

Mapping Center Answer:

The Image Analysis window, new at ArcGIS 10, presents the most commonly used processes in easy to use interface. The processing is applied to the raster, mosaic dataset, image service, or Web Coverage Service (WCS) layers (not the data) on-the-fly.

In the case of hillshade, a hillshade function is applied on-the-fly and produces a temporary layer. So you can save that raster layer result on the disk, as you mentioned. The saved result would be same as the Spatial/3D Analyst hillshade result. The shaded relief button in the Image Analysis window will apply a multi-color coloramp by default. This produces a multi-band result. For a hillshade, you would typically change that to grayscale colorramp. Once that's done, you will get single band result.

This functionality does not replace the Spatial/3D Analyst hillshade tools. As you noted, those shortcut buttons are removed from the toolbars in ArcGIS 10, but you can add them back to the interface using the Customize Mode in ArcMap.

Also, ArcMap 10 has new command line called the python window. You can run geoprocessing tools like Spatial Analyst hillshade directly from that window.

As I mentioned earlier, saved results from the Image Analyst hillshade would be similar to the Spatial/3D Analyst hillshade. You would only find differences in temporary layer. In the temporary layer, the Z factor hillshade is dynamically applied and will increase or decrease as you zoom out or zoom in. However, the results would be the same at resolution fo the input raster (which is why the saved results will be pretty much teh same as those from Spatial/3D Analyst). This behavior will most likely change in next release as it would behave the same as the Spatial/3D Analyst hillshade.

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