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Raster Layers

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RasterLayers are one of the fundamental data types in Openwind and have been discussed in several sections already. In Openwind, the term "raster" essentially means a regular grid of numeric values.



Figure 77:   RasterLayer Properties: Display Tab


In general, it is preferable to use RasterLayers over VectorLayers. Querying a RasterLayer involves a single lookup to a memory address per axis (two: one for X and one for Y), whereas querying a VectorLayer generally involves carrying out trigonometry and/or line crossing checks which tend to be more processor-intensive.



Figure 78:  RasterLayer Properties: Color Scale Tab


RasterLayers can be used for almost anything in Openwind, including terrain elevation, roughness length, combining multiple layer validities, ZVI output, shadow flicker output, noise output, wind speed maps, terrain gradients, vegetation heights, ground porosity, environmental energy losses and so on.

See the Interpretation (Section 8.3) for an explanation of assigning meaning to PolygonLayers.

The Output Legend button can be used to output an image containing the legend information for use in an external desktop publishing software.

Raster data can be converted using the Reclassify tab of the raster properties. The interface is slightly different depending on whether the original raster contains discrete integer values or continuous floating point values.

For continuous values, bands are used as in figure 79. The user specifies the upper limit of each band and acts as the lower limit for the subsequent band. An example of this kind of conversion would be converting bathymetric data to foundation cost multipliers.

For integer values a one to one conversion can be used as in figure 80. An example of this kind of conversion would be converting land cover classes to roughness lengths as in the figure below.



Figure 79:   RasterLayer Properties: Reclassification of Continuous Values





Figure 80:   RasterLayer Properties: Reclassification of Discrete Integer Values


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