topic Scallop Shaped Edges on Interpolation in ArcGIS Mapping and Charting Questions

Scallop Shaped Edges on Interpolation

BrittanyHoffnagle — Tue, 28 Mar 2017 18:38:31 GMT

I am trying to use Natural Neighbor Interpolation on a set nodes (100,000's) to create a raster surface that has a grid resolution of 1x1 meter. When I symbolize the raster to be n=0 clear, and n>0 my specific color ramp I created, the edge of the n>0 extent is scallop shaped. Is anyone familiar with this and know how to solve this without using 3D analyst?

Re: Scallop Shaped Edges on Interpolation

NeilAyres — Tue, 28 Mar 2017 18:44:28 GMT

"scallop shaped".

Can you show us a picture of what you mean?

Re: Scallop Shaped Edges on Interpolation

BrittanyHoffnagle — Tue, 28 Mar 2017 18:49:16 GMT

Re: Scallop Shaped Edges on Interpolation

BrittanyHoffnagle — Tue, 28 Mar 2017 19:19:32 GMT

I posted a picture!

Re: Scallop Shaped Edges on Interpolation

DanPatterson_Retired — Tue, 28 Mar 2017 19:48:38 GMT

If you have a grid resolution of 1 m... there is no need to interpolate, just convert to raster using a cell size of 1.5 or 2. You are going to get no extra 'precision' doing an interpolation, as your data is suggesting

Re: Scallop Shaped Edges on Interpolation

NeilAyres — Wed, 29 Mar 2017 06:38:19 GMT

But what is the problem with what you have got?

The raster interp seems to be doing exactly what is required.

I take it that the white dots have very low values of whatever it is you are measuring and the blue dots are higher values.

Re: Scallop Shaped Edges on Interpolation

BrittanyHoffnagle — Wed, 29 Mar 2017 12:59:12 GMT

The scallop or bubble shape in between the white dots. White dots are 0 and the blue is anywhere between 1 and 100. Because of the NNI, there is some excess interpolation out to the white dots. So between the Blue and white dots there is data that doesn't actually naturally occur. We to get rid of the "scallop shape".

Re: Scallop Shaped Edges on Interpolation

BrittanyHoffnagle — Wed, 29 Mar 2017 13:01:10 GMT

Our point feature class shape file is not a 1 m grid. We want to interpolate to a 1 meter grid. The problem lies in the scallop shape interpolated edge between the Blue dots and the white (0's) dots. The green yellow and red raster is showing the issue.

Re: Scallop Shaped Edges on Interpolation

DanPatterson_Retired — Wed, 29 Mar 2017 15:44:10 GMT

It is the data spread then as Neil suggests. if you don't want the scalloped edges, then you would have to clip around a bounding extent

Re: Scallop Shaped Edges on Interpolation

BrittanyHoffnagle — Wed, 29 Mar 2017 15:51:54 GMT

Clip is an option but could be tedious because there are areas of 0's within the raster as well, so we would want to get rid of the scallop along those edges as well and to create a boundary that covers my entire extent would be a long time commitment. Not sure if there is an easy answer to this. The real question, I guess, is whether is a tool to smooth interpolation edges.

Re: Scallop Shaped Edges on Interpolation

NeilAyres — Wed, 29 Mar 2017 15:55:37 GMT

I think you are expecting "interpolation" to do something it is not designed to do. It will interpolate between low and high depending on the decay function.

So, if you do not think this is "real", do as Dan_Patterson says, make a clip polygon and clip out the bit that you "like".

Re: Scallop Shaped Edges on Interpolation

DanPatterson_Retired — Thu, 30 Mar 2017 00:43:45 GMT

No... you can define masks or clip to constrain the output results, but there is no 'function' to feather the edges to make them look more pronounced