6

I have ASCII files in *.xyz format and want to generate a DEM out of it. According to the information about the data the *.xyz files are containing variable grid widths - from 1 meter to 4 meter. Following a small section of the data (converted to points): enter image description here

Is it possible to generate (with interpolation) a raster with a resolution I want (1,2,3 or 4 meter)? If I generate a 1-meter-raster out of it, how is the quality of the resulting raster in your opinion?

I use ArcGIS in general.

  • 1
    You probably want to calculate the average point spacing and use that figure as a guide in determining the DEM resolution. It looks as though there isn't a wild amount of variation in point coverage from your figure above. Calculating average point spacing with Arc isn't too hard: webhelp.esri.com/arcgisdesktop/9.3/… – WhiteboxDev Nov 12 '14 at 12:49
  • 2
    The right answer may come down to understanding why the widths are variable. Regardless, it certainly depends on what your accuracy requirements are (compared to the accuracy of the data). If the spacing has been adapted to the local ruggedness of the terrain, then the wider spacings may occur in places where interpolation is likely to be accurate over relatively long distances. If the spacing was chosen to achieve a higher accuracy than you need, then datasets generated with spacings much smaller or much larger than any spacing in the original data could be fine for your purposes. – whuber Nov 12 '14 at 15:32
  • 1
5

The concern that I have is that lidar is not a systematic sample, as shown in your example. This data appears to have already been gridded and then thinned based on terrain or vegetation variation. Given the short-distance variation and observed spatial pattern of the clustering, my guess is higher point spacing was retained due to vegetation (e.g., trees). One question would be if this point data is bare-earth or does it have vegetation retained?

If this data has, in fact, been pre-gridded then applying an interpolation with a higher resolution than the observed point spacing may propagate bias from whatever previous algorithm was applied. This could give you something akin the the derivative bias observed in 10m USGS DEM's.

That said and bias aside, the higher resolution spacing is likely supported regardless of application. If you are after vegetation and it is present in the points then you would want the resolution it is represented as. If higher density represents higher terrain variation then the 4m spacing is more homogenous and, if the processing procedure was valid, the higher resolution is supported.

This is, of course, all predicated on the assumption that the data was thinned, based on some sort of homogeneity/heterogeneity criteria, is correct. Other than for specific analytical purposes, I do have to admit that I am completely baffled as to why one would do this.

2

If you are not in an urban area, interpolating elevation from 4 meter point density to 1 m grid is quite safe, especially if your 1 m spacing reflects a larger roughness of your terrain (e.g. river bed). Make sure that you use an exact interpolator to preserve the elevation at known points, because LIDAR is precise and accurate.

1

You say you have ArcGIS, but you will need the Spatial Analyst or 3D Analyst extensions. I agree with the above comments. Use IDW or Natural Neighbor interp in SA. Set up the extent and the cell size using the environment settings. Could also build a TIN from these points then use the TIN to Raster tool.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.