topic Re: Hillshade - Stretched not rendering as expected in ArcGIS Spatial Analyst Questions

Hillshade - Stretched not rendering as expected

JakubSisak — Wed, 01 Sep 2010 18:49:50 GMT

Hello all,
Please see the attached for visual... Used the province of Manitoba dem to generate a hillshade. Result is Symbolized with streched values, Standard Deviation, n: 2 Display Resampling: Bilinear Interpolation.

As with other hillshades, I was expecting the stretched values but it almost appears as this hillshade was classified with unique values.

I would like to produce a smooth hillshade. Help would be much appreciated.

Re: Hillshade - Stretched not rendering as expected

ChrisSnyder — Thu, 02 Sep 2010 20:25:37 GMT

Just specify a stretch type of None and it should look okay... That's what I do at least.

An annoying fact: If you calculate statistics for a raster, it automatically applies a stretch to the symbology (standard deviation by default). Not sure why its is like that, nor why ESRI would by default assume most users would want to apply a complex stretch factor to their raster symbology. Hmm...

Re: Hillshade - Stretched not rendering as expected

RobertBerger — Thu, 02 Sep 2010 20:40:07 GMT

Raster options does allow you to turn off the stretch by default. At ArcGIS 10 you can also change the default stretch to other stretches.
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Setting_default_raster_display_options/009t0000008z000000/
Enjoy.

Robert

Re: Hillshade - Stretched not rendering as expected

ChrisSnyder — Thu, 02 Sep 2010 20:52:35 GMT

Is this only for v10? In v9.3 under the "raster" options there is a check box for "Display raster layers with contrast stretching" which is checked off by default (so you would then think that a stretch would not be used). I find that as long as a raster has had the stats calculated for it (no matter if the box is checked or not), the stretch renderer kicks in every time. One of the most notable display issues I have with this is that it makes my hillshade models appear darker than the should. The only way I can get it to NOT use the streatch by default is if I delete the .aux file and have ArcMap rebuild it (without stats).

Re: Hillshade - Stretched not rendering as expected

ChrisSnyder — Thu, 02 Sep 2010 20:54:47 GMT

Verified... The ability to turn off the stretch is new in v10 (v9.3 lacked the "Raster Layer" tab).

Re: Hillshade - Stretched not rendering as expected

RobertBerger — Fri, 03 Sep 2010 14:56:06 GMT

The option to toggle between various stretches is new at v10. At 9.3.1 you do have the option to turn contrast stretching on/off (meaning you either get standard deviation stretch or none stretch).
http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=About_setting_default_raster_display_options

Robert

Re: Hillshade - Stretched not rendering as expected

JakubSisak — Thu, 09 Sep 2010 13:15:54 GMT

Thanks for your replies. The option to toggle between various stretches was available in previous versions. What might be new is the ability to define what type of stretch is being used by default when the raster is added to the map. The above described rendering anomaly does not go away by adjusting the type of the stretch. Using None or Minimum-Maximum rather than St. Deviation just makes the hillshade darker and less pronounced. The anomaly is not as visible because it is obscured by the uniform shades but it is still there.