Hello Everyone,

 

Last week I had posted a question to the Listserv regarding smoothing contours created from DEMs derived from LAS Datasets and if there were any standards that dictated how much smoothing was acceptable. Initially I had created contours using the contouring tools in 3D Analyst and then smoothed the contours using the smoothing functions found in the cartography toolset. I received a number of responses and some suggestions that smoothing the DEM before creating the contours was a good approach. As a test I decided to try smoothing the DEM using

“Filter” in the Spatial Analyst toolbox with the filter type set to low. Below is a brief summary of each of the methods I used to create 1ft contours.

 

Method 1:

Contours were created directly from the DEMs using the Contour tools in 3D Analyst. The contours were then smoothed using “Smooth Line” tool in the Cartography toolset with a PAEK algorithm value of 20ft. The resulting contours were also “flagged” to show errors (contour lines crossing, etc.). The contours that were smoothed using this methodology yielded a dataset

that will require a significant effort to clean up.

 

Method 2:

Contours were created from a second DEM that was smoothed using the “Filter” tool . The contours created using this method required much less cleanup and appeared to provide a better

product for production/cartographic applications.

 

As for the which method provided more precise contours it is difficult to say. Going forward I will maintain two sets of contours. One will be used primarily for analysis and the other for production/cartographic applications.

 

I would like to thank everybody that responded to my questions and to Andy Kuether, Roy Apostle, and Glenn Hazelton for suggesting the DEM smoothing approach.

 

Eric

 

Eric Rizzo

GIS Administrator

City of Waltham

21 Lexington Street

Waltham, MA 02451

Tel: (781) 314-3006