topic Re: Contours to DEM creates pixelated DEM in Elevation Data Questions

Contours to DEM creates pixelated DEM

KarlBackhaus — Wed, 28 Aug 2019 23:49:54 GMT

Hey all,

I am currently trying to create a DEM from ~1800 control points. Elevation ranges from 1820ft to 120ft. I created contours from a DEM generated by the contours. I have continuously had issues with the output rasters being extremelty pixelated. The pixeIs are generally 200m by 160meters using the NAD 1983 Zone 18N coordinate system. The default pixel size using the Topo to Raster Tool and Tin to Raster is 1.88159924474218E-03. Is there a step I am missing or anyway to resolve the issue?

Re: Contours to DEM creates pixelated DEM

DanPatterson_Retired — Thu, 29 Aug 2019 00:00:48 GMT

sounds like your dem has decimal degree coordinates. That cell size may be too coarse.

How many rows and columns do you have? by default the extent is divided by 250 to yield the cell size, which would lead to coarse results in any case.

As a suggestion, it would be best to use a projected coordinate system. In any event, this help topic is useful for making decisions on raster creation

How the Cell Size Projection Method environment setting works—Geoprocessing | ArcGIS Desktop

Re: Contours to DEM creates pixelated DEM

KarlBackhaus — Thu, 29 Aug 2019 00:26:13 GMT

I have 109 columns and 249 rows. I am using the NAD 1983 Zone 18 as my projected coordinate system, is there a projected coordinate system that is should use that is similar? Also, should I have this coordinate system from the start?

I have the jist of some GIS things but this has always tricked me. One of my former classmates made a similar map using bedrock topography elevation points, created contours and made a DEM from them. He then subtracted the Surface Elevation DEM from the Bedrock topography to get drift thickness and it turned out very smooth and at a cell size of 10 X and 10Y to match the surface DEM. That is ultimately what I am trying to do but the DEM is too coarse.

Re: Contours to DEM creates pixelated DEM

DanPatterson_Retired — Thu, 29 Aug 2019 00:39:07 GMT

If the dem is coarse already, you have few options if you can't acquire or redo the dem.

Have a look at

How Contouring works—Help | ArcGIS Desktop

which provides a few tips on improving the 'quality' (in quotes) of the contours.

Re: Contours to DEM creates pixelated DEM

KarlBackhaus — Thu, 29 Aug 2019 01:01:54 GMT

I can go back to step 1 with the point data. They started in WGS_1984. I should reproject them to a UTM Coordinate system such as NAD 1983?

Then convert the points to a raster by Kriging? Create the contours using the contour tool and set a small cell size? The DEM that I will be subtract from is 1m in resolution.

Re: Contours to DEM creates pixelated DEM

DanPatterson_Retired — Thu, 29 Aug 2019 01:18:17 GMT

Project to UTM NAD83 would be a good start. Follow that link about the projection cell size that I listed.

Interpolate …

Hopefully your points are numerous and well distributed in space or you will have problems with any method of interpolation.
Select an appropriate cell size given the number of points and their distribution and spacing (art meets science to some degree)
Assuming that you have determined that Kriging, in some variant, is the most appropriate interpolator (that is a much longer discussion),
Contour, using a 'smoothing filter' for aesthetics.

After all this, if you contours are all blocky and weird looking, take a hard look at the input data... it may not be enough, it may have a poor spatial distribution, the interpolator isn't appropriate for the data or myriad of other issues.

If you just want a smooth look and aren't looking for anything else, have a gander at spline interpolation

Good luck