The Tasmania 2 metre Digital Elevation Model (DEM) is a regular grid of ground level elevation values spaced at 2 metre intervals across the extent of the land area of Tasmania and most of the associated islands, but excluding Macquarie Island. Approximately 65% of the DEM is derived from LiDAR data, with the remainder of the surface interpolated from photogrammetric contours, spot heights and mean high water level data. Outside of LiDAR areas, the data resolution is 10 m. The projection is GDA 1994 MGA Zone 55, with vertical heights relative to AHD. This dataset was produced by Mineral Resources Tasmania and the data is available to download using the ELVIS download portal. https://elevation.fsdf.org.au/

This DEM was constructed from a combination of data sources, including LiDAR data, 10 m photogrammetric contours, spot height data, mean sea level (MSL), and mean high water level (MHWM). Processing was primarily performed in an automated manner, using ArcGIS Pro and a series of python scripts. The LiDAR data includes 178 surveys collected between 2008 and 2020, by a variety of providers and for a number of different purposes. Data was supplied in LAS file format and were first (re)classified to ensure that bridges were classified separately. The LiDAR data was then processed using ESRI LAS dataset tools, to create a bare earth DEM for each dataset. The surveys were ranked by year and quality and the DEMs clipped according to rank, leaving a 50 m overlay between overlapping acquisitions, prior to mosaicking the datasets. In order to fill areas where LiDAR was unavailable, a Default DEM was constructed using ESRI Topo-To-Raster from 10 m photogrammetric contours, spot heights, MSL, MHWM and Hydro-Tasmania lake bathymetry. This data was clipped with the LiDAR coverage, leaving a 25 m overlap, and then mosaicked with the LiDAR DEM using a distance weighted average.

Position Accuracy: The 2 m DTM has been constructed from 178 LiDAR surveys from 2008 to 2020, and in areas without LiDAR survey from a photogrammetric 10m contour data set. That data set has been prepared to support the Tasmanian Strategic Flood Mapping Project with a minimum model resolution of 10m. There were 12,410 records for survey control marks in Tasmania available (as per data download from 11/06/2020); of these 8,718 have been excluded from the analysis for the following reasons: * Location outside the LiDAR acquisition areas * Location outside the DTM area * Status other than existing * Unsuitable horizontal or vertical order * Height datum other than AHD83. Of the remaining 3288 were appropriate for the first analysis. An analysis of the DTM and 3288 overlaying survey control marks within the LiDAR acquisition areas showed that 94% (3100) of the height values compared are within a vertical accuracy of 0.5m. For the 94% within the 0.5m vertical accuracy, 58% (1799) are within 0.1m, 27% (847) are greater but within 0.2m, 10% (299) are greater but within 0.3m, 3.4% (108) are greater but within 0.4m, and 1.6% (49) are greater but within 0.5m. The remaining 6% of the height values ranging within a vertical accuracy from 0.5m to 11.8m were partially referring to survey control marks which are not suitable for the DTM validation analysis for the following reasons: * Location off ground level (including locations on top of bridges, buildings, lookout platforms, in pits and culverts) * Location with strong variation in terrain height (including locations near embankments and in rocks) * Possible loss of survey control mark due to construction works (including roadworks). Where the DEM was derived from photogrammetric data the accuracy is consistent with the Tasmanian 1:25000 topographic map series, in which 90% of well-defined data is within 12.5 m of true horizontal position, and 90% of vertical data is within 5 m of true position. This accuracy may not be maintained in obscured areas affected by vegetation or other obstructions, or in areas of very steep topography. Attribute Accuracy: Data is from a range of sources, spanning several decades, but mostly from the best hardcopy sources available or field observation by MRT staff. All reasonable effort has been made to ensure these occurrences are accurately attributed. Logical Consistency: The data used to construct the DEM has been compiled from a range of sources, spanning several decades, with a range of data capture technologies and specifications. As a result there is variation in the logical consistency of the data across Tasmania. The elevation values are consistent in relation to the source data at all locations tested. Completeness: Statewide coverage including King and Flinders Islands, but excluding Macquarie Island.