IDW with a clipped geometry

[RachelS]

Hi,
Can anyone tell me is there a way to use IDW with a clipped geometry.
I have 10 polygons with points inside them. I only want the interpolation to run within the polygons as they are not related to each other.
I tried the input barrier polyline option by converting the polygons to polylines but this didn't work and still interpolated outside the polylines.

Any help much appreciated.
Regards
Rachel

[MarcinGasior]

You can try using raster analysis mask:

- In IDW tool dialog window click Environments
- In Raster Analysis section select your polygon layer as Mask

[SteveLynch · Accepted solution]

Hi,
I tried the input barrier polyline option by converting the polygons to polylines but this didn't work and still interpolated outside the polylines.

The barrier option in IDW uses a "line of sight" technique to determine which points are used when making a prediction at a location. Therefore, for example, if you have high values to the left of a barrier and low values to the right then your output will have a clear "split".

The mask option that is suggested by m.gasior clips the output after all the interpolation has been done.

You have to decide what you want, viz.,
- predictions should be influenced by the barrier, then use the barrier option
- clip the output after interpolation is done then use the mask environment option.

Hope this helps
Steve

[RachelS]

Thanks for you replies,
It looks like I'll use the polyline barrier as I want adjustments made before the interpolation rather than after with the mask.
Many thanks
Rachel

[SteveLynch]

Rachel

If you also have Geostatistical Analyst and ArcGIS10+ I would suggest that you try Kernel Interpolation With Barriers

The advantages include; optional standard error of prediction output and it does not use "line of sight" but rather "shortest distance around the barrier".

REgards
Steve