ah-docs

Build Contours

Description

Generates contours from Digital Elevation Model (DEM) raster data. User can specify contour interval and starting elevation and optionally limit the processing extent to an area of interest using a limit polygon. Contours are post-processed to enhance readability.

The post-processing methodology is based on workflows designed for the National Resource Conservation Service (NRCS) National Enterprise Elevation Project (NEEP) and includes:

• Step 1 (Generate) - Initial contour lines are generated using the Contour geoprocessing tool from the Spatial Analyst toolbox with a contour interval of 2 feet.
• Step 2 (Simplify) - Contour lines are run through the Simplify Line tool from the Cartography toolbox to remove vertices, reduce disk size and improve processing speed. The tool uses the Douglas-Peucker algorithm to retain critical points with a simplification tolerance of 10 centimeters.
• Step 3 (Smooth) - Once simplified, contour lines are passed through the Smooth Line tool from the Cartography toolbox to enhance visual interpretation and remove any jaggedness resulting from coarse raster cell sizes. This step uses the PAEK algorithm with a smoothing tolerance of 10 meters.
• Step 4 (Clip) - If provided, the input AOI is buffered by 10 meters during step 1. This step then uses the input AOI to Clip the resulting smoothed contours back to the intended area.
• Step 5 (Remove) - If provided, contours shorter than specified length will be removed.

The methodology produces best results on high-quality (resolution) DEMs.

Usage

Parameters

Parameter Name	Type	Direction	Data Type	Dialog Reference
Input DEM Raster	Required	Input	Raster Layer	Raster dataset/raster layer for which contour lines will be constructed. The methodology produces best results on high-quality (resolution) DEMs.
Contour Interval	Required	Input	Double	Number in DEM vertical units defining interval between the contour lines.
Output Contour Feature Class	Required	Output	Feature Class	Output feature classes hosting the constructed contour lines.
Base Contour Elevation	Optional	Input	Double	Starting contour elevation.
Input Limit Polygon	Optional	Input	Feature Set	AOI - Defines the area within which the contour lines will be constructed.
Remove Short Contours	Optional	Input	Linear Unit	Length of short contours that will be removed. If greater than 0, any contours with length less than provided value will be removed. If set to 0, no contours will be removed.If Remove_Short_Contour=0, all the resulting contour lines will be kept.There is no python reference for this parameter.