topic Re: Does the Web App Builder's Analysis Widget "Interpolation" tool have trouble with overlapping points in a layer? in Developers Questions

Does the Web App Builder's Analysis Widget "Interpolation" tool have trouble with overlapping points in a layer?

LeighJeudevine — Thu, 24 Jan 2019 15:55:17 GMT

I am configuring a web app for water quality samples taken at 4 different sites along a bayou. The point layer has 242 records a/k/a 242 point features. However, when I run the AGO Interpolate tool (via the Analysis widget) I get an error message claiming that there have to be at least 10 points available. Interpolation procedures worked great in desktop. Is the fact that the points are overlapping only 4 locations (same x, y's) causing a problem in AGO? Or is this a bug?

Thanks for the feedback!

Re: Does the Web App Builder's Analysis Widget "Interpolation" tool have trouble with overlapping points in a layer?

EricKrause — Thu, 24 Jan 2019 16:17:34 GMT

It actually needs 10 unique locations with measured values. All measured values at the same location get averaged into a single value.

The same thing should happen in Desktop though, unless you happened to change the default value of the "Coincident Points" environmental setting. Which tool are you running in Desktop that can execute successfully with these points?

Re: Does the Web App Builder's Analysis Widget "Interpolation" tool have trouble with overlapping points in a layer?

LeighJeudevine — Thu, 24 Jan 2019 17:21:19 GMT

Thank you for that explanation for the AGO tool logic.

I was able to perform several IDW and Kernal Interpolation with Barriers

tests. The results varied, but I did not knowingly change the

environmental settings other than to set a shapefile of the bayou as the

extent and/or barrier. Here is a snapshot of the mask I extracted from

results for Dissolved Oxygen with IDW on desktop:

Re: Does the Web App Builder's Analysis Widget "Interpolation" tool have trouble with overlapping points in a layer?

EricKrause — Thu, 24 Jan 2019 18:57:30 GMT

That explains it; I should have thought of this earlier. IDW and Kernel Interpolation With Barriers both only require 3 unique locations to run. Interpolate Points actually uses Empirical Bayesian Kriging (EBK) to perform the interpolation, and that method requires at least 10 unique locations. You should get an analogous Not Enough Data error if you try to use the EBK tool with this data.

More data is needed in EBK than in IDW and Kernel Interpolation because many more parameters must be estimated in EBK, and more data is required in order to do that.

Re: Does the Web App Builder's Analysis Widget "Interpolation" tool have trouble with overlapping points in a layer?

LeighJeudevine — Thu, 24 Jan 2019 18:59:43 GMT

Got it...Thank you for this information!

Re: Does the Web App Builder's Analysis Widget "Interpolation" tool have trouble with overlapping points in a layer?

EricKrause — Thu, 24 Jan 2019 19:02:35 GMT

Also, if you really want to use EBK with those points in ArcMap or ArcGIS Pro, you can use the Coincident Points geoprocessing environment to force the tool to use all the points and not perform any averaging. Set the environment to INCLUDE_ALL in order to do this. However, you should keep an eye out for artifacts in the output because including all points with a relatively few number of sample locations will very frequently cause instability and strange behavior in kriging methods.

Re: Does the Web App Builder's Analysis Widget "Interpolation" tool have trouble with overlapping points in a layer?

LeighJeudevine — Thu, 24 Jan 2019 19:10:17 GMT

The end result was intended to be an online tool where people can view water quality features and see potential changes as more data is collected over time. It is a school project has already spanned several years. However this info is great to keep in mind for other uses!