Title

Merged Tiles - Ausgeoid09 - DEM 

Time period

2012-02-062012-03-09 

Horizontal Accuracy

0.3m  

Vertical Accuracy

0.1m  

Code

MGA Zone 55 GDA94 

Title

ESRI Ascii 

Topic category

• Elevation

Use limitation

General 

Classification

Unclassified  

Description

The surrounding adjacent LiDAR projects incorporated in the merged tiles are: 2011 Melbourne Structural Vegatation LiDAR - Lara, Victorian Coastal LIDAR Level 3 Classification, 2013-14 Geelong-Anakie-Golden Plains LiDAR 1) ArcGIS 10 Terrain Grids were derived using the Natural Neighbor interpolation. This method uses the closest triangles and applies weights to the proportionate areas from the grid cell centroid to interpolate the value. It uses known elevation data, it does not make any predictions regarding the surface and accurately depicts existing troughs and peaks in the data and supports irregular point spacing, which suits the nature LiDAR data. Grids were then translated to ESRI ASCII formats using custom ArcGIS and Feature Manipulation Engine (FME) macros. 2) For comparison, two separate datasets were generated, one referenced to AHD using Ausgeoid09 and a 2nd dataset referenced to AHD using Melbourne Geoid model. The dataset referenced to AHD using Ausgeoid09 reveals a marginally better fit to test points. A tilt in a general east-west direction was observed when the LiDAR data was compared to field test point sites spread throughout the project area. A tilt correction has been applied to both Ausgeoid09 and Melbourne Geoid datasets. 4) Cut lines were used to merge the adjacent datasets together. An overlap of 50m was used between adjacent/overlapping datasets. Cut lines have been made around ground features that have changed between the dates of the new and existing data within overlap areas. New reprocessed data has been kept in preference to existing data. Below are approximate locations of where changes in ground features have occurred. Adjustments to cut lines have been made in these locations: 264590E, 5773165N; 269210E, 5771650N; 270540E, 5757320N; 271690E, 5770390N 

Classification

Unclassified  

Attribute Quality

Positional Accuracy

Conceptual Consistency

Comments

Meets all specifications and adheres to format and naming standards. An assessment of the merged tiles for DTM consistency was undertaken across all project edges. In general the edgematching was adequate and any stepping between source datasets is within reasonable limits. However, in one particular instance, the redevelopment and widening of the Midland Highway between the dates of the 2 LiDAR surveys in question has resulted in a significant step (>0.25cm and up to 0.6m) in the merged product. This is an unfortunate and unavoidable effect of mergeing data over changed land surfaces. 

Missing Data

Comments

This data set represents the edge tiles of the original AOI that have overlap with adjacent projects.The tiles are full with respect to data content and consist of merged data from the source project and the adjacent projects. 

Excess Data

Platform Type

Aerial  

Assembly

Single  

Tile Size

2 km  

Raster Type

DEM  

X Pixel Resolution (cm)

1cm  

Y Pixel Resolution (cm)

1cm  

Seamlessness

Full  

Number of Bands

1 

Band List

1  

Resampling Kernel

Cubic Convolution  

Rectification Type

Orthorectified  

Platform Name

Fixed Wing Aircraft  

DEM Creator

Supplier