# Thread: Problem with minimum range while intepolating bathymetry

1. ## Problem with minimum range while intepolating bathymetry

Hi,
i have such a problem that i need to interpolate bathymetry for a strait, with grid cells of about 50 or 100m. In the data i have depths from 0.2 - 8m. Now my problem is that using any interpolation method (IDW, kriging, natural neighbour) i get values starting from the depth of 2m, although the most of the strait is relatively shallower than 2m. I also tried to interpolate as a spline, but that didn't also work out. Is there a way i could define the lower limit to my interpolation or what can i do to solve this problem?

2. ## Re: Problem with minimum range while intepolating bathymetry

If your input has a min=0.2 and you're not seeing it in the output.

Do you have coincident (duplicate) points, if so, eliminate them.
How close is the nearest point to the one with 0.2?
What happens if you make your cell size smaller?

-Steve

3. ## Re: Problem with minimum range while intepolating bathymetry

I tried to make it with really fine cells, then it creates some weird results ranging from -1 to 17. There is no overlapping points and the points are scattered with distance of about 500-700m between them.

4. ## Re: Problem with minimum range while intepolating bathymetry

IDW can never give you -1 if the min=0.2

If you don't get exactly 0.2 or the max value in the output raster then it means that these input locations do not fall on the cell center of the output raster.

-Steve