Generating topos / contours for earthwork software or Google Earth

QGIS is an excellent piece of free GIS software. This tutorial explains how to use Site Scan and QGIS together to generate topo/contour plots for earthwork, client updates, planning civil work, and accurately estimating jobs.

  1. Drag and drop both “mesh_ortho.tif” and “mesh_dem.tif” into the QGIS canvas

    Sometimes the DEM might show up with “no data” pixels.

    You can change the symbology by zooming into a building or tree using “mesh_ortho.tif”, right-clicking on “mesh_dem.tif” and selecting “Stretch using Current Extent”, as illustrated in the following three images.

    After the DEM is stretched to the current extent, it will display appropriately

  2. Zoom into the area of interest where you'd like to create your contours.

  3. Navigate to raster clipper via Raster>Extraction>Clipper.

  4. In the Clipper dialog box, use the “mesh_dem” as the input file, and select a filename and location for the new clipped raster file. Then, select the extent of the clip by dragging in the map canvas to create a rectangle.

    Note: You can also clip using a .shp file if you would prefer a non-rectangular-shaped region.

  5. Now, create contours by navigating to the Contour tool via Raster>Extraction>Contour.

    In the Contour dialog box, select the newly created clipped raster as the input and select an output filename and file type.

    You can produce contour/topos in the following formats:
    1. KML / KMZ (Google Earth)
    2. DXF (Autocad)
    3. .SHP (Esri)
    4. And many other file formats

      For the contour interval, remember the dataset is in meters. To create 1 foot contours, enter the value “0.304”. Check the box to include an elevation field.

      In a couple seconds, the contour shapefile will be created.

  6. Right click the newly created file which now appears in the Layers window and select “Save As”.

    Once saved, you can use this file in whatever planning or earth work program you need.  

  7. To create a KML file for viewing in Google Earth, select “Keyhole Markup Language” as the output format, and select a filename for the output file.

  8. Open resulting KML file in Google Earth!


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