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An example of the various options, that can be completely mixed is shown in the below picture.
coverageTileArchiveLayer
Since 2013.01 FEWS enables using a compressed grid file for your DEM. The compression is done per scale and in tiles and archived in a zip file, pretty similar as openStreetMap works.
You can prepare a CTA (coverage tile archive) with the F12 menu in the explorer (F12 -> convert -> convert ascii grid to coverage tile archive).
As the resulting file should be in meters (see below why) you may need to specify a conversion factor from eg. centimeter to meter. You can also define an accuracy of the compressed values. Normally centimeter accuracy is more than enough, sometimes you can easily go to decimeters, which compresses much better of course. For synchronization reasons you may want to split the resulting file in parts of e.g. max 2 GB. Usually this is more than enough. The resulting compression is generally a factor of about 10-20. But the main reason is the much better performance of the GUI as per pixel is already determined which value should be plotted.
A very useful additional feature (to be used in the griddisplay only) is the feature that you can use the CTA as a real DEM and use it for plotting of water depths.
You then can easily display the water depths per pixel, based on a time series with water levels (using global datum!) and the DEM in the CTA. Therefore simpy enable the property useAsLocalDatumReference. The waterlevels can have any spatial distribution, like grid or polygon and should not have the exact same grid definition as the DEM. The calculation of the depths is completely on the fly and no depths have to be stored in the database.
| Code Block | ||||||
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<coverageTileArchiveLayer id="asc">
<file>petten.cta</file>
<visible>false</visible>
<useAsLocalDatumReference>false</useAsLocalDatumReference>
<classBreaks>
<lowerColor>brown</lowerColor>
<upperColor>green</upperColor>
<lowerValue>-4</lowerValue>
lowerValue>-1</lowerValue>
</classBreaks>
</coverageTileArchiveLayer>
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| Code Block | ||||||
|---|---|---|---|---|---|---|
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<gridPlot id="Petten">
<timeSeriesSet>
<moduleInstanceId>Floodmap</moduleInstanceId>
<valueType>grid</valueType>
<parameterId>H.sim.hist</parameterId>
<locationId>Floodmap_grid</locationId>
<timeSeriesType>simulated historical</timeSeriesType>
<timeStep unit="minute" multiplier="1"/>
<readWriteMode>read only</readWriteMode>
</timeSeriesSet>
<classBreaks>
<break lowerValue="0" color="light blue" opaquenessPercentage="25"/>
<break lowerValue="1" color="blue" opaquenessPercentage="75"/>
<break lowerValue="2" color="purple" opaquenessPercentage="75"/>
</classBreaks>
<geoMap>
<geoDatum>Rijks Driehoekstelsel</geoDatum>
<projection>mercator</projection>
<defaultExtent id="Petten testmodel">
<left>-1000</left>
<right>10000</right>
<top>4000</top>
<bottom>0</bottom>
</defaultExtent>
<extraExtent id="Nederland">
<left>-200000</left>
<right>500000</right>
<top>750000</top>
<bottom>200000</bottom>
</extraExtent>
<scaleBarVisible>true</scaleBarVisible>
<northArrowVisible>true</northArrowVisible>
<labelsVisible>true</labelsVisible>
<backgroundColor>light blue1</backgroundColor>
<openStreetMapLayer id="osm" name="Open Street Map">
<url>http://tile.openstreetmap.org</url>
<cacheDir>$MAP_CACHE$/openstreetmaps</cacheDir>
</openStreetMapLayer>
<coverageTileArchiveLayer id="asc">
<file>petten.cta</file>
<visible>false</visible>
<useAsLocalDatumReference>true</useAsLocalDatumReference>
<classBreaks>
<lowerColor>brown</lowerColor>
<upperColor>green</upperColor>
<lowerValue>-4</lowerValue>
<lowerValue>-1</lowerValue>
</classBreaks>
</coverageTileArchiveLayer>
</geoMap>
</gridPlot>
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layer
Definition of a GIS layer to be displayed.
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