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Interpolation dans ArcGIS Online ou analyse spatiale ArcGIS

warrenroberts

Je me demande s’il existe un moyen d’obtenir de meilleurs résultats avec l’interpolation dans ArcGIS Online, comme avec l’IDW dans Spatial Analysis. L’image ci-dessous montre l’interpolation réalisée avec ArcGIS Spatial Analysis et, à droite, le résultat de l’analyse d’interpolation dans ArcGIS Online.

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DanPatterson_Retired

Warren... were the input parameters the same in terms of the conventional tool ?

IDW—Help | ArcGIS for Desktop

Were the dataset both in projected coordinates? (they should be btw)

DarrenWiens2

I couldn't find the link to the AGOL interpolate points tool method, but the similar (same?) tool through the ArcGIS REST API states that it uses empirical Bayesian kriging, which will produce different results than IDW:

Interpolate Points—ArcGIS REST API: Spatial Analysis Service | ArcGIS for Developers

As for how to force AGOL to do IDW, no clue.

XanderBakker

The help inside the Interpolate ArcGIS Online, contains about the same information as found here in the documentation: Perform analysis—ArcGIS Online Help | ArcGIS . ... but doesn't reveal much about the method. I guess the links provided by Darren are best thing to go on, but I feel the documentation should shed some more light on the interpolation method used.

There are many ways to interpolate in ArcGIS for Desktop and some of them are described in this rather old document: http://www.esri.com/news/arcuser/0704/files/interpolating.pdf

NeilAyres

If you want one button click to give you a "nice" picture, use AGOL.

If you want some control over the output and you know the data and what might be appropriate, use the tools in SA.

If you really want to spend a lot of time on the job, use GeoStat Analyst....

warrenroberts

funny. I tell my students, if they want the best results they can go out and dig up the whole bloody field and no need to guess :-). But in the end .. I often have a class of only an hour of non GIS users ..and I may add 90% are Mac users.

warrenroberts

I'd have the points projected in local projection while online, I didnt think it would help .. I'll give it a try. The parameters are different only because their less, or perhaps simpler setting in AGOL

NeilAyres

Interpolation can be a really tricky thing. And it all depends on the data and the nature of the variable you are trying to interpolate and what sort out output you need and what it might be used for.

DanPatterson_Retired

Yes...I get the point, It would be nice to do at least a comparison of one "thing" in two platforms and get the same result. I wouldn't even go to a Kriging demo when interpolation and its "bloody field" isn't the point you are trying to make on a small demo. It is a rare case where the method is specified in the help and in some cases, the algorithm isn't mentioned. Good luck

XanderBakker

I just added feedback to the documentation on this analysis with a reference to this thread. Hopefully they will add some explanation.

Eric6346

Thank you for this feedback. As others have noted, Interpolate Points does not use IDW for the interpolation. Instead, it uses Empirical Bayesian Kriging (EBK), which we consider to be our best automatic interpolation method.

We will add extra information about the particular EBK settings that are used in Interpolate Points to the REST API documentation in the near future, but for now, this is what you need to know. Most parameters from EBK are controlled by the "Optimize for" parameter in Interpolate Points. This parameter has three setting: Speed, Accuracy, and an unnamed default option that I will call "Medium".

If you choose the "Speed" setting, EBK will use the following parameters:

Data transformation type: NONE
Semivariogram model type: POWER
Maximum number of points in each local model: 50
Local model area overlap factor: 1
Number of simulated semivariograms: 30
Number of neighbors: 8

If you choose the "Medium" (default) setting, EBK will use the following parameters:

Data transformation type: NONE
Semivariogram model type: POWER
Maximum number of points in each local model: 75
Local model area overlap factor: 1.5
Number of simulated semivariograms: 100
Number of neighbors: 10

If you choose the "Accuracy" setting, EBK will use the following parameters:

Data transformation type: EMPIRICAL
Semivariogram model type: K_BESSEL
Maximum number of points in each local model: 200
Local model area overlap factor: 3
Number of simulated semivariograms: 200
Number of neighbors: 15

You can learn more about these parameters here. Let me know if you have any other questions.

XanderBakker

Hi Eric Krause , thanks for getting back on this topic so fast. +1 for that and if I could I would add another +1 for the content of the information. Great intel, would like to see that in the documentation too.

Eric6346

Update: This information has been added to the Interpolate Points REST API documentation, and it can be viewed here:

Interpolate Points—ArcGIS REST API: Spatial Analysis Service | ArcGIS for Developers

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