Title

Victorian Coastal Continuous Seamless Digital Elevation Model 

Alternate title

VC-DEM_CONTINUOUS-SEAMLESS_2017JUL14 

Purpose

Slope and slope classes, Aspect Insolation, Drainage network, Hydrological indicies and water table indicies, Climate variables, Input to estimation of soil parameters, Input to land component and soil type mapping, Viewshed analysis, Visualisation, Environmental modelling including salinity, species distribution, spread models etc. 

Supplemental Information

Current Design Issues: A DEM with wide general use is required, that is, the DEM must ideally meet the needs of a wide range of users. This implies a need for the highest possible quality model. Hydrological soundness is maximised by using the ANUDEM software. Interpolation is to a 20m grid. For some derivations it may be necessary to interpolate the DEM to a finer resolution. Continuity with surrounding sheets is essential. Future Design Issues: The cell size may need to be reviewed. The procedures may need to be reviewed in flat, featureless terrain where contour data are sparse. Related Documents: None 

Status

Completed  

Horizontal Accuracy

25m  

Code

4283 

Maintenance and update frequency

Not planned  

Title

ASCII tiles 3 

Topic category

• Elevation
• Environment
• Geoscientific information

Classification

Unclassified  

Statement

Dataset Source: Bathymetric data supplied by Deakin University, Port of Melbourne and the Royal Australian Navy combined with exiting DELWP DEM datasets including the 2010 VCDEM, the 2014 Western Port DEM and National Elevation Data from Geoscience Australia to successfully create this new product. Dataset Originality: Derived 

Description

Preparation 1. Acquire high resolution data from Deakin University, PoM and DELWP 2. Analyse datasets for project suitability 3. Convert suitable datasets to raster format if provided in LAS or XYZ formats 4. Convert horizontal datums to GDA94 (if not already) 5. Convert heights to AHD (if not already) 6. Check the datasets fit vertically with the 2010 VCDEM by comparing the difference of any overlap between input datasets and the 2010 VCDEM 7. Determine order of highest quality/most recent to lowest quality/oldest datasets where overlap occurs 8. Clip (remove) any distinct triangulation from derived rasters Seamless Continuous DEM 1. Identify significant gaps in the Updated High Resolution DEM 2. Identify low resolution datasets suitable for filling the significant gaps 3. Aggregate/resample high and low resolution datasets into 10m cell resolution 4. Create a smoothed low resolution DEM for the whole coastline extent by a. combining the Updated High Resolution DEM with the Australian Bathymetry and Topography Grid b. aggregating the output then resampling it to 10m cell resolution using a cubic function 5. Clip low resolution datasets to areas of significant gaps e.g. coastal areas out to three nautical miles and Port Phillip Bay 6. Perform smoothing on a major section of the Port Phillip Bay product from step 5 to remove gross triangulation in the center of Port Phillip Bay 7. Combine the Updated High Resolution VicGrid94 product with the low-resolution datasets ensuring there is a gap between the two across which interpolation can occur to ensure there is a smooth transition 8. Interpolate all remaining gaps in the dataset to ensure that the DEM is one continuous product a. Aggregate and classify the combined DEM to areas with elevation (purple) and areas with NoData (green) b. Perform a shrink function to shrink the region that had elevation data (green) c. Use map algebra to isolate the cells shrunk from the original elevation data. This will be the cells along the edges of the high resolution data d. Create points for each cell and attribute it with the elevation data. These will be used for the interpolation e. Convert the original classification raster (see step a.) to polygon and isolate the polygons where there is NoData within the desired DEM extents f. Interpolate between points using the ANUDEM interpolation algorithm with the polygons defining the extents of the interpolation area g. Mosaic interpolated data with original data 9. Review the continuous product for areas where artifacts arise from gross differences 10. Repeat step two but clip the low-resolution data so that it reduces significant artifacts when interpolating 11. Repeat steps 2-7 until the major discrepancies are removed 12. Mosaic interpolated data, high-resolution data and low-resolution data into a VicGrid94 TIFF 13. Re-project VicGrid94 TIFF DEM into MGA Zone54 and 55 section TIFFs 14. Convert both MGA TIFFs and the VicGrid94 TIFF to 5km ESRI ASCII grid tiles 

Classification

Unclassified  

Attribute Quality

Comments

Not Relevant 

Positional Accuracy

Comments

Precision: 20m grid resolution; otherwise determined by topographic base. Bias: determined by topographic base Determination: The DEM is fixed to the topographic base maps 

Conceptual Consistency

Comments

Visual and computational coverage checks ensured the input datasets were represented in the final product and heights still aligned with input data. 

Missing Data

Comments

Will be completed on a needs basis, however the DEM can be readily generated for any tile with topological TOPO25 data. Complete Victorian Coastline 

Excess Data