DEM of MSP offices, produced by gridding LiDAR data and overlaying intensity map.

Digital elevation models are created by gridding LiDAR data. In gridded data, each cell is assigned a value based on surrounding elevation points. This gives the data a continuous distribution resulting in a smooth surface when displayed.

Once the LiDAR is in grid format, Digital Elevation Models (DEM), and contour and shaded relief maps can be created.

A closer view of a location.

X,Y,Z View of the LiDAR

Gridded View of the LiDAR

The Ground Truthing Site (GTS) is a ground survey of a test area; we use specially made targets that show up well in the LiDAR due to the intensity of the light that is reflected back. The LiDAR cloud can be compared with the surveyed GTS. A patch of LiDAR can be statistically analysed in order to test the vertical and horizontal accuracy of the LiDAR. It is then possible to adjust the LiDAR to best fit the surveyed test site. We also measure the offset on the aircraft so that we know how far the GPS antenna is to the laser center.

The image on the left shows a ground truthing site with a raised target. If you move your cursor over the image, you will see the survey data with LiDAR points overlaid. The green coloured points have a level greater than that of the grassy area and the raised target is clearly visible in the scan. The levels of the LiDAR points are compared to the surveyed levels for vertical accuracy analysis.

The LiDAR is processed automatically to seperate the returns into ground and vegetation files. This allows us to create 'bare earth' models without buildings or trees. The LiDAR can be processed in order to produce a variety of products including contour maps, cross-sections and digital elevation models (explained in information bar on the right). Once the point cloud has been processed into grid format (DEM), a variety of maps can be made, including shaded relief maps, vector maps (showing water flow), 3D perspective maps, slope maps, hillshade maps and ortho-drape maps. We can also compute volumes from the DEM's and have analysed differences between DEM's on beaches to quantify changes in beach volume. In combination with cross sections, we were able to show how wave action was affecting the beach profile.

TRANSFORMATIONS AND GEOID / ELLIPSOID MODELLING - Aerial laser scanner systems compute positions and heights using GPS. The GPS system uses the WGS84 ellipsoid to reference it's heights. If you want to accurately convert these heights to a more usable geoidal height (eg height above sea level), then you need an accurate model of the geoid, local to your area of interest. Accuratemaps Survey Partnership have developed software solutions that allow for the conversion of huge data quantities from one co-ordinate system to another.