topic Re: Help with the slope tool in ArcGIS Spatial Analyst Questions

Help with the slope tool

GrahamMcCulloch — Mon, 21 Nov 2011 22:20:34 GMT

I'm trying to use the slope tool on hilly national elevation data from the seamless server but the output keeps coming out completely red. From what I understand the xy and z data is all in meters so I shouldn't need to convert the data to or from feet. I tried rerunning the tool using 3.048 and .3048 in the z field but it keeps coming out all red.

Can someone help me with this?

Re: Help with the slope tool

DirkCilliers — Tue, 22 Nov 2011 11:41:06 GMT

Hallo G,

Just to be clear, is the result "all red" when you keep the z value 1 as well? What is the projection of your dataset?

Dirk

Re: Help with the slope tool

GrahamMcCulloch — Tue, 22 Nov 2011 16:55:05 GMT

Hi D,
Thanks for replying.
Yes, everything is red even with the z value left at 1.
The data frame coordinates are in NAD 83.
Thanks,
G

Re: Help with the slope tool

DanPatterson_Retired — Tue, 22 Nov 2011 18:24:11 GMT

What is the projection?
NAD83 is a datum, not a coordinate system.

Re: Help with the slope tool

GrahamMcCulloch — Wed, 23 Nov 2011 16:40:41 GMT

I hadn't been using a projection, just the original datum, so I presume that's the source of my problems?

I have been trying to define a projection (NAD 83 CORS96 UTM Zone 10N) but am having strange results so I'll have to sort that out first.

Re: Help with the slope tool

DanPatterson_Retired — Wed, 23 Nov 2011 20:14:25 GMT

It may that your coordinates are in decimal degrees (aka a Geographic Coordinate system with a NAD 83 datum) and defining the coordinate system incorrectly isn't going to work. It needs to have a defined coordinate system first ... if it doesn't have one use the Define Projection tool. If it does have one then you need to project it to what you want. Projection produces a new file. Check your data source and see if it has a defined projection, if it does, then Project it to what you want.

Re: Help with the slope tool

GrahamMcCulloch — Wed, 23 Nov 2011 22:32:59 GMT

I used the Define Projection tool to project the Elevation data to NAD 83 CORS96 UTM Zone 10N (all it had before was a GCS in NAD 83) but when I run the slope tool it still comes out all red, except for some some green areas which I believe are lakes. It's the same whether I leave the Z value as 1, 3.048, or 0.3048.

Any suggestions as to what I should try next?

Re: Help with the slope tool

DanPatterson_Retired — Wed, 23 Nov 2011 22:41:11 GMT

Again, the Define Projection tools does not project the data, it just makes it wrong if it is defined wrong, you need to project the data using the appropriate tool

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00170000007q000000

On a side note, ESRI, change the name of the Define Projection tool as per the ArcGIS Ideas suggestion
https://c.na1.visual.force.com/apex/ideaView?id=087300000008MkXAAU
please vote, the confusion is prevelant and needs to be addressed.