topic Re: Extending spline beyond points in Geoprocessing Questions

Extending spline beyond points

DarrenHeffernan — Sat, 21 Dec 2013 16:27:02 GMT

Hello,
I'm trying to overlay a spline on a map, but can't figure out how to interpolate beyond the points used to generate the spline...
I've tried changing the properties to extend it to the data frame, but this doesn't seem to work.
Any help appreciated,
Darren
[ATTACH=CONFIG]30063[/ATTACH]

Re: Extending spline beyond points

MarcoBoeringa — Sat, 21 Dec 2013 20:54:47 GMT

Interpolating beyond the extent of the data points is actually called extrapolation. You should be very weary of doing this with any "interpolation" method, even when it is supported, as it can result in really wacky values for calculated raster points outside the extent of the data points. This is especially true for methods like Spline.

In addition, looking at your dataset as presented by the screenshot you included, which seems to be based on a mere 7 points, the results of any interpolation will be highly speculative. I really think your dataset is far to small for any reliable interpolation, and therefor question whether you should continue with this.

Re: Extending spline beyond points

808707 — Mon, 23 Dec 2013 08:35:49 GMT

What are you trying to interpolate exactly? A cheat is to make some values up and place them at the corners of the area you want to include. However this will completely mess up your interpolation values and is just for visualisation purposes.

Re: Extending spline beyond points

SteveLynch — Mon, 23 Dec 2013 13:11:48 GMT

I agree that you have too few points.

You don't need to put points at the corners.

In the environment you need to specify an output extent, the default is the extent of the input points.

-Steve