Kriging Barrier Polyline

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09-01-2011 03:33 AM
PaulEvans
New Contributor II
Dear all,

I am trying to create a raster dataset from a vast number of bathymetric data points. I want to use the kriging method with a cell size of ~20m but when I create the raster surface it is interpolated beyond/outside the zone where the points are located resulting in a surface that is fine within the point area but is incorrect outside. I know that a barrier polyline can be used for the IDW interpolation method to prevent this from happening but does anyone know a way of doing this in the kriging method as the barrier polyline option is not available?

Regards,

Paul
5 Replies
TonyPagani
New Contributor
Hi Paul,

You can limit the area where the interpolation will be done by setting a mask in the environments. To do this you will need a polygon feature class/shape file or a raster which delimits the area of your interpolation. When you open the kriging tool, click on the Environments button. Under Raster Analysis set the mask to the polygon or raster. This will limit the interpolation to this area.

Here is a link to the online help regarding masks: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//001w0000001t000000.htm

Regards,
Tony
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SteveLynch
Esri Regular Contributor
There is a huge difference between the barrier option and using the MASK.

IDW's barrier option uses a "line of sight" method to determine which points will be used in the interpolation. I.e if I can see you, I'll use you. The barrier also has infinite height.

MASK on the other hand is done after the fact. I.e after the interpolation is done the area is clipped or masked.

Spatial Analyst has 2 interpolation methods that use barriers. Geostatistical Analyst, from Version 10, also has 2 barrier interpolators and these use a non-Euclidean distance approach.

Hope this helps.
Steve
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PaulEvans
New Contributor II
Thanks for your responses. So I am guessing the MASK function isn't as effective as the barrier option as the MASK is undertaken after the rater interpolation is complete, i.e. the interpolation process outside the point area has been undertaken and the MASK tool is just cropping the raster back to the specificed polygon? Is this the same as using the extract by polygon tool once the raster has been created?

From experience, which interpolation methods would you recommend in order to create a high resolution raster surface (mainly for visualisation purposes only) from dense point data using a polyline as a barrier to prevent the interpolation from going outside the area of interest? The IDW method seems to crsh when I try and create a raster using a polyline barrier shapefile?

Thanks again,

Paul
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SteveLynch
Esri Regular Contributor
Paul

As far as the crash is concerned, please contact Esri Support or email me (slynch@esri.com) the data and the parameters that you are using and which version of ArcGIS.

As far as which interpolator to use. I would suggest some initial exploratory analysis. Use the CreateSubsets GP tool to create a training and testing subset. Also look at cross validation.

Regards
Steve
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EricKrause
Esri Regular Contributor
Bill is right.  Interpolators are good at, well, interpolating.  Unless you have an expert understanding of the physics involved with the process (and build your model around the physics), extrapolated predictions will be unreliable.

You can force the interpolators to make predictions as far outside the data extent as you want, but this is generally a very bad idea.  If you build the model correctly, you can trust the predictions within the data extent, but you should be very careful about any conclusions you draw outside that extent.
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