EOTopo: Production of EOTopo Maps

Thursday, Jan 11, 2018 at 17:45

ExplorOz - David & Michelle

  • A new MapScript program was developed by David Martin (I.T. Beyond Pty Ltd) to build tiles at 5000x5000pixels.

  • The 200K final whole of the country image is built using 37 x 30 tiles of 5000 pixels. This produces 1147 tiles and is over 80.1GB of GeoTiff files.

  • The 144K final whole of the country image is built using 50 x 42 tiles of 5000 pixels. This produces a staggering 2193 tiles and is over 153GB of GeoTiff files.

  • The GeoTiff files used for the raster map products use a projection of WGS84 (EPSG:4326). This projection is in most respects exactly the same as GDA94 and was chosen as it is the worldwide standard for Lat/Long projected maps.
  • These tiles are then processed into a Virtual Raster File. This is the bridging of each of the tiles into a single file so that it can be processed and rendered as a single image.

  • The State definitions are made using QGIS – an Open Source Geographic Information System. The states polygon vector files were built from the GeoScience base framework layer with a buffer set around the state borders of 0.1 degrees. This ensures that the state borders are fully visible on each of the maps.

  • Another process is then used written using GDAL - Geospatial Data Abstraction Library. This script cuts up the Virtual Raster into each state file.

  • GlobalMapper (a GIS Data processing application) is used to create the GeoTiff and ECW files. The ECW State files use a 10:1 compression ratio and the Australia single image uses 15:1 compression (this reduces the quality a little of the single ECW tile).

  • GeoTiff files were converted to the OZF4 file format (using the Neural Net Colour Reduction set at 70% and 256 colours) using the Img2Ozf program from OziExplorer.

  • The OZF4 files total 7.04GB, the ECW files total 6.67GB and the ExplorOz Places Name Search totals 10MB.


Projection/Datum
- Datum: WGS84 (EPSG:4326)
- Projection: Geographical – latitude and longitude

Geographic Bounding Box
Australia
UPPER LEFT X=112.8214505824
UPPER LEFT Y=-8.9737047371
LOWER RIGHT X=153.7385256655
LOWER RIGHT Y=-43.8423972383
COVERED AREA=15824079 sq km

NSW/VIC
UPPER LEFT X=140.8618525527
UPPER LEFT Y=-28.0574625534
LOWER RIGHT X=153.7385256655
LOWER RIGHT Y=-39.2984700000
COVERED AREA=1490991 sq km

NT
UPPER LEFT X=128.9004800000
UPPER LEFT Y=-10.8658878240
LOWER RIGHT X=138.0990599969
LOWER RIGHT Y=-26.0986200000
COVERED AREA=1646244 sq km

QLD
UPPER LEFT X=137.8946600000
UPPER LEFT Y=-8.9737047371
LOWER RIGHT X=153.6987010041
LOWER RIGHT Y=-29.2789930169
COVERED AREA=3755777 sq km

SA
UPPER LEFT X=128.9012600000
UPPER LEFT Y=-25.8963800015
LOWER RIGHT X=141.1028899182
LOWER RIGHT Y=-38.1607942767
COVERED AREA=1570545 sq km

TAS
UPPER LEFT X=143.7187423533
UPPER LEFT Y=-39.0984700000
LOWER RIGHT X=148.5984253999
LOWER RIGHT Y=-43.8423972383
COVERED AREA=214584 sq km

WA
UPPER LEFT X=112.8214505824
UPPER LEFT Y=-13.5902843515
LOWER RIGHT X=129.1018600000
LOWER RIGHT Y=-35.2919118880
COVERED AREA=3983519 sq km
David (DM) & Michelle (MM)
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Always working not enough travelling!
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