I'm trying to extract aspect surfaces from different DEM sources at different resolutions in QGIS. I've had success working with SRTM-derived grids (3-arcseconds) and am trying to perform the same gdal-based functions on Canadian DEMs (0.75-arcseconds). My issue is that there are very distinct boundaries between elevation levels and it's causing my aspect calculation to have plateaus.

SRTM Aspect Grid

USGS SRTM aspect grid

Canadian DEM Aspect Grid

Canadian DEM aspect grid

I'm wondering what I'm doing wrong here or if I'm forgetting something. I'm not sure if I should be smoothing my DEM out or if there's anything the can be done to the Aspect grid to make it continuous.

  • 2
    The second grid looks like the result of a wrong parameterized interpolation or triangulation of contour lines, except the mountain in the south-east. Can you verify that the Canadian DEM is continuous/smooth, and not already leveled?
    – Detlev
    Jan 23, 2016 at 10:50
  • @Detlev I checked over some of the problematic areas and realized that it's an issue with how the data was compiled. While the lowlands are relatively flat, there is some variation (as can be seen in the SRTM data) but the model used in the CDEM has leveled terrains for the flatter lowland areas. I probably need to smooth out the CDEM first if I want to create continuously sloping surfaces. Thanks for the question! Jan 24, 2016 at 22:12


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