Elevation or ground surface information for many years has been portrayed by contour lines drawn on a map. These contours have been obtained photogrammetrically from stereo imagery created from the aerial photography. The contour information has been adequate for mapping but with the advent of GIS and better technology it has become unsuitable data for high-end ground surface analysis and accurate planning.
The main reasons for this are: the coarseness of the data (despite some areas of five metre contours, most of the state is only covered by ten metre contours) and the accuracy of the data with the contours being captured from small scale photography. Also this type of capture is performed visually and anywhere the ground surface is obscured by vegetation or shadow it increases the possibility of errors in the contour data.
Remote sensing technology has provided new methods for capturing ground elevation data. Radar, LiDAR and point cloud capture systems are now used to provide high resolution data at an accuracy previously unattainable. The three methods of capture all have advantages and disadvantages but the most important issue is that the data provided by these methods it often better than the existing contour data and enables more accurate and comprehensive analysis of the ground surface.
LiDAR surface model Southern Outlet, Hobart
is the most often used of the three technologies, at this point in time, as it provides a good compromise between number of ground point readings and coverage and is able to penetrate all but the densest vegetation canopy. It cannot be used in cloudy conditions. Aircraft are the normal platform.
Radar is more suited to quick acquisition of large areas and satellites as well as aircraft can be used as the platform. It has the ability to penetrate cloud but struggles to penetrate vegetation cover due to the non-vertical nature of the radar beam.
Point Cloud elevation data
Point Cloud Elevantion Data - Tamar Valley
is a by-product of imagery capture. Stereoscopic digital imagery enables each imagery pixel to not only have a horizontal position assigned but also a vertical value. As the Point Cloud data is derived from imagery, any object or vegetation obscuring the ground will cause a problem for identifying the ground height at that point. It has a very high point density and is best suited to small open areas of capture.
Apart from 10 metre and 5 metre contour data and the 25 m DEM, all the elevation data available from this department is LiDAR derived.
An index of the LiDAR coverage of Tasmania is available on LISTmap
. Please note that the index only indicates coverage areas and not general availability. Some of the LiDAR data is proprietary information owned by other organisations. The index will provide either access to the data or indicate who the holds the data. Other organisations owning the data may be able to provide access.