topic IDW Problem How to define an interpolation limit? in ArcGIS Spatial Analyst Questions

IDW Problem How to define an interpolation limit?

ElaHorold — Sun, 08 Jun 2014 07:28:45 GMT

Hey guys,

I'm working on a project in which I have the target to determine the mud amount of a lake. I would like to make an interpolation with the IDW methode. However, I have the problem that the limits of my interpolation are the external measurement points. But I would like to have the lakeborder as limit. Is this possible? Or do I have to use another methode?
I desperately need help so every suggestion is more than welcome!
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Greetings

Re: IDW Problem How to define an interpolation limit?

DanPatterson_Retired — Sun, 08 Jun 2014 13:37:04 GMT

Did you try setting a mask in the Environments tab for the IDW interpolator?
http://resources.arcgis.com/en/help/main/10.2/index.html#//009t000000nz000000
http://resources.arcgis.com/en/help/main/10.2/index.html#//001w0000001t000000

Re: IDW Problem How to define an interpolation limit?

ElaHorold — Tue, 10 Jun 2014 08:48:10 GMT

Thank you for answering 🙂
But I think I have solve my problem.
I have fixed imaginary measuring points on the shore of the lake.
The values �??�??of these measurements are all 0.
By performing an interpolation with all all measuring points, even with the imaginary points and the actual points, I get a good result.

After conversion to a TIN I could reload the file in ArcScene. It looks like a good terrain model 🙂

Please tell If this way of solving the problem is not a good way.
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Re: IDW Problem How to define an interpolation limit?

DanPatterson_Retired — Tue, 10 Jun 2014 08:55:08 GMT

The 0 values around the edge will affect the interpolation results in the intervening cells within the study area. It may look nice on screen but the interpolated values close to the edge may be spurious. I wouldn't recommend it.

Re: IDW Problem How to define an interpolation limit?

SteveLynch — Tue, 10 Jun 2014 14:12:00 GMT

I agree with Dan, however, I would suggest the following;

- convert your coastline to polyline if not already a polyline (use FeatureToLine tool)
- IDW with;
1) original points (without the zero's)
2) use the above polyline as a barrier
3) set the extent (in the environment) to the polyline

or
IDW with
1) original points (without the zero's)
2) set the extent (in the environment) to the polygon boundary
3) set the mask (in the environment) to the polygon boundary

-Steve

Solution without interpolation ...

ElaHorold — Mon, 16 Jun 2014 15:50:28 GMT

Hey Guys,

first of all thank you!
Today I had a very useful conversation with a GIS professor of my university. He advised me to the following solution:
In the attribute table of the shoreline add another column for the height.
This gets the value 0 (On the shore of the lake: Lake depth and water depth = 0)
Now an TIN surface can be created with the tool "Create TIN (3D Analyst)".
Select the shoreline and the measurements as Inputfeatures (The heightfield values �??�??then have to be changed correctly).

Solution without interpolation ...

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