Sink Evaluation - Can't update ZUnit

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04-02-2013 02:22 PM
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ChristinaMetherall
New Contributor
Hi,

I am attempting to run the Sink Evaluation tool (after using the Sink Prescreening tool), but I get the error "Spatial Reference does not have z unit. Z factor computation did not succeed. Do you want to use a factor of 1?"

As suggested, I attempt to modify the prj.adf file, and I save it, and then re run Sink Evaluation, but I get the same error. The prj.adf files I am modifying are in the local directory in Layers/PreFillDeM and Layers/Sink. When I open the prj.adf files in Notepad they seem to continuous lines of text (i.e.no new lines after each parameter). I change the text following ZUnits from NO to0.017... (my DEM Z units are in degrees), being sure to keep the same spacing, etc. I am not sure why I still get this error. Any help you can give wqould be greatly appreciated!
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ChristineDartiguenave
Esri Contributor
Is your grid projected or in geographic? What is the xy unit?

Christine Dartiguenave
Esri Water Resources Team
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BrodySunderland
New Contributor
Hi Christine,

I�??m having the exact same issue as Christina and based on your comment I�??m beginning to think it has something to do with the coordinate system. I�??m working with a projected county coordinate system with xy units in feet. I�??d like to work with integer z units (also in feet) with the precision of a tenth of a foot but I can't get the prj.adf zunit to remain at 10.

Would you recommend projecting from the county system to a more common coordinate system?

Thanks a bunch,
Brody
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ChristineDartiguenave
Esri Contributor
It looks like the culprit is the auxiliary grid file. If a projection is specified in that file, it will be used to update the prj file when the grid gets added to ArcMap. This file is usually located in the same directory as the grid directory (as long as it is writable) and named grid.aux.xml where grid is the grid name. It contains information associated to the grid that cannot be stored with the grid itself.

http://resources.arcgis.com/en/help/main/10.1/index.html#//009t00000027000000

You can set the correct zunit in the auxiliary file by using the geoprocessing tool Define Projection and specifying the Z Coordinate System as well. Then either pick an existing one or create your own.
In the Vertical Coordinate System Properties window you will have the option to specify 1/ZUnit under Linear Unit. You can pick an existing unit (e.g. feet, decimeter, etc.) and see the corresponding value for 1/zunit (e.g. centimers = 0.01 meters/centimeters corresponding to zunit=100 in projection file).

The tool will edit both the auxiliary file and the xml.

Christine Dartiguenave
Esri Water Resources Team
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