GRAFCAN launches “DSM on steroids”

GRAFCAN has launched a new product based on LiDAR for the Canary Islands: a digital suface model (DSM) that is literally “on steroids”. It is a synthetic view (not image-derived) that lets the user intuitively understand the territory. The product combines standard hillshading with a height-based color-coding enabling the viewer to “see” where the trees are taller and to grasp height differences between buildings. Darker shades of green indicate high vegetation and lighter shades of green indicate low vegetation. For man-made structures, the shade of red is darker for taller buildings and lightest for one-story houses. The new product is available for all of the Canary Islands at a resolution of 2.5 meters/pixel via the GRAFCAN Web viewer and also as a WMS service.

Example of a DSM on steroids: The viewer intuitively grasps the height and spatial distribution of trees in vegetation areas and the density and size of buildings in urban areas.

Example of the new DSM on steroids: The viewer intuitively grasps the height and spatial distribution of trees in vegetation areas and the density and size of buildings in urban areas.

The product is complemented with a layer with the water areas and a layer of the main roads (both extracted from topographic maps). Around the airports the terrain is very flat and mostly empty. Therefore an intensity map was extracted from the LiDAR and fused into the imagery to provide additional details.

Comparison between orthophoto and DSM on steroids: The ridge is practically invisible in the ortho and the dark green colors of the vegetation are quite missleading to the untrained eye.

Comparison between orthophoto and DSM on steroids: The ridge is practically invisible in the ortho and the dark green colors of the vegetation are quite missleading to the untrained eye.

The LiDAR was flown between 2011 and 2012 with a Leica ALS60 with an average density of 1 pulse per square meter. Most of the LiDAR processing was done with LAStools batch scripts:

  • clean-up of header with las2las.exe
  • orthometric height correction with lasheight.exe
  • tiling with lastile.exe
  • bare-earth extraction with lasground.exe
  • noise removal (clouds and low points) with lasheight.exe
  • DSM rasterization at 2.5 meters per pixel with las2dem.exe
  • flattening reservoirs, ponds, swimming pools with las2dem.exe
  • normalize LiDAR to height above ground with lasheight.exe
  • create height above ground map with lasgrid.exe
  • generating intensity rasters for airports using LiDAR with lasgrid.exe

Other processing tasks involved ArcGIS and Photoshop:

  • separate height above ground map into vegetation and building height map with ArcGIS
  • generating hillshaded rasters from the DSM with ArcGIS
  • rasterizing building footprints colored by height with ArcGIS
  • rasterizing roads from topographic maps with ArcGIS
  • rasterizing reservoirs, ponds, swimming pools with ArcGIS
  • extracting water line of Ocean (contour at 1 meter) from DSM with ArcGIS
  • some manual editing on complex areas (classification errors, ocean line…) with ArcGIS
  • fusing airport intensity rasters into hillshade rasters with Photoshop
  • blending all the layers into the final product with Photoshop
Comparison between bare earth DTM and DSM on steroids. The green houses show up nicely as "planar low vegetatation". This is because they are made out of coarse maze fabric (instead of glass) that lets the the laser through and does not deflect it (like glass houses would).

Comparison between bare earth DTM and DSM on steroids. The green houses appear as “low planar vegetatation”. They are made out of coarse maze fabric (instead of glass) that lets the laser through and does not deflect it (like glass would).

GRAFCAN is a company that  produces and publishes the geographic information of Canary Islands. The company has done LiDAR flights since 2010. You can explore the Canary LiDAR directly in 3D via their interactive Web viewer of IDECanarias (press the “Lidar” button).

Another beautiful example of a DSM on steroids.

Another beautiful example of a DSM on steroids.