Rendering Floating Georaster

Question

Hi
I am new to Georaster. I have an ArcInfo grid which I exported to Tiff and loaded to Oracle as a Georaster using Mapbuilder. The Mapbuilder does not seem to create color map table as SDO_GEOR.getColorMapTable returned null.
The Tiff has floating number as values. I want to create a thematic map (actually a base map for Oracle Maps application using MapViewer). So I need to classify this Georaster based on its values and render it accordingly using different colors for different value range (e.g. value < 30 will have red, 30-60 will have blue, etc.). Can anyone please tell me how to do it?
Thanks a lot.
Sudip

Answer 1

the easiest way to do a test on a colormap is to use an existing colormap. For example, a typical color GIF image contains a colormap. you can load it into georaster. assume you have a georaster object which contains a colormap now, you can call getColormap on that object and then set the colormap into another georaster object. before you set it you might want to do some editing on the colormap to fit into your needs and make sure it's compatible with the image.
----- you wrote --------
3. Another suprising thing was, when I checked for colorMap, it returned null for layer 0 and 1 while using:
SELECT sdo_geor.getColorMap(georaster,0) from LHDENSITY;
SELECT sdo_geor.getColorMap(georaster,1) from LHDENSITY;
Any idea why I am getting two layers (0 and 1) while uploading just a single-image to Oracle?
this is correct. in GeoRaster layer number 0 means the whole object while layer number 1 means the first band (even though you have only one band). a colormap of layer number 0 applies to all sublayers in georaster.
you called setColorMap(grobj, 0, cmobj) to setup the colormap to the object layer and so it applies to the first band too. there is NO duplicate of the colormap in the object itself. you'd better call setColorMap(grobj, 1, cmobj) in your case.
For floating numbers, you can set up a colormap easily if you have the colormap known. the georaster manual is not clear on this and will be fixed in the upcoming release. actually the cellValues in the colormap implies value ranges: Assuming (cellValue1, red1, green1, blue1, alpha1) and (cellValue2, red2, green2, blue2, alpha2) are the two neigboring entries in ascending order in the colormap, the implied value range is [cellValue1, cellValue2) and the color components associated with all cells in this range is (red1, green2, blu2, alpha2). The cell value range is always inclusive in its lower boundary and exclusive in the upper boundary. The size of each range does not necessarily have to be the same. Taking the same example, the range is equal to or greater than cellValue1 and less than cellValue2. For lower cell depth (e.g., 1 bit to 8 bits integers), the cell value ranges are typically the same as the cell values.
So, to do a quick test, you can use the above rule to quickly create a few meaningful entries in the colormap for your floating number grid.
For pure test purposes, you might want to create a color GIF file and load it into georaster.
can you display your color image in GeoRasterViewer? Always use the GeoRasterViewer and SDO_GEOR.validateGeoraster to validate the object and so the colormap first, whenever you edit the object.
With MapViewer and MapBuilder, could you please post the log?
regards,
Jeffrey