2

I am having trouble producing a hillshade using the ArcGIS spatial analyst (hillshade) tool. I am working with a 1m DEM in a projected coordinate system (GDA_94_MGA56) and have adjusted the Z-factor accordingly for a metric dataset to 0.0000898 (dataset is at -28 degrees). Everytime I try to output, all values in the raster are returned as 180. Any ideas please?

enter image description here

and the output looks like so:

enter image description here

  • 5
    How does it look without z adjustment? You've made all elevations close to 0. – FelixIP Jan 29 '18 at 7:27
1

As was mentioned by @FelixIP, you need to ignore the Z Factor. Leave it at 1.

From the documentation:

If the input raster is in a spherical coordinate system, such as decimal degrees, the resulting hillshade may look peculiar. This is due to the difference in measure between the horizontal ground units and the elevation z units. Since the length of a degree of longitude changes with latitude, you will need to specify an appropriate z-factor for that latitude. If your x,y units are decimal degrees and your z units are meters, some appropriate z-factors for particular latitudes are:

Latitude     Z-factor
 0           0.00000898
10           0.00000912
20           0.00000956
30           0.00001036
40           0.00001171
50           0.00001395
60           0.00001792
70           0.00002619
80           0.00005156

It seems that this is where you got the value of 0.00000898. However, if your latitude is at -28 degrees, then, it seems reasonable that you should have used the value for 30 which is 0.00001036. However, that is only if your x,y coordinate system is in decimal degrees.

You're using the projected coordinate system GDA_94_MGA56 which has x,y units of metres. Therefore, you can use the default value of 1 because the elevation of the DEM is also in metres (presumably).

Also from the documentation, the z factor is the:

Number of ground x,y units in one surface z unit.

The z-factor adjusts the units of measure for the z units when they are different from the x,y units of the input surface. The z-values of the input surface are multiplied by the z-factor when calculating the final output surface.

If the x,y units and z units are in the same units of measure, the z-factor is 1. This is the default.

If the x,y units and z units are in different units of measure, the z-factor must be set to the appropriate factor, or the results will be incorrect. For example, if your z units are feet and your x,y units are meters, you would use a z-factor of 0.3048 to convert your z units from feet to meters (1 foot = 0.3048 meter).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.