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Download Raster Data

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Elevation Data – This function can be used to download SRTM elevation data. At present the two sources are 3 arc second (90m) quality-controlled data and 1 arc second (30 m) raw data. The data is in 1 degree tiles. Openwind initialises the latitude and longitude range based on the current map extents but it also fills a drop down list with the extents of the workbook as well as the extents of each layer in geographic coordinates.

 

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Figure 81:   Download Elevation Data

 

If multiple tiles are requested, Openwind stitches them together into one raster layer. The data is in geographic coordinates and so Openwind needs to resample the data into the current projection. It does this at around half of the original resolution in an attempt to avoid degrading the information in the original. The resulting raster is set to interpolated terrain elevation.

Land-cover Data – This function can be used to land-cover data and is very similar to the elevation data download above. The source is a mix of data from different sources. We rely on the NLCD 2001 database in the US, Corine in Europe and Australia and Geocover LC otherwise (for the 3 arc-second LCC data).

Openwind uses nearest neighbour resampling to assemble a single landcover raster layer in the workbook projection. Openwind also throws up a dialog with the Olsen land-cover classes along with descriptions and roughness lengths. The values in this dialog can be copied and pasted to and from a spreadsheet programme. They can also be edited in place. The table as a whole can then be saved to text file for future use.

 

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Figure 82:   Olsen Land-Cover Classes

 

 

 

 

 

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