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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
Kjell- Kjell Røang wrote:
Hi I want to resample a grid in lat/lon to a grid in a projection and do the transformations myself. Both grids has a rectangular topology and the projection grid has also has a rectangular geometry. Then, what will be most efficient:
Instead of doing the transformations yourself, why not just let the CoordinateSystem do this? If you want to display the lat/lon grid on a different projection, you could use a Display side CoordinateSystem. See visad/examples/MapProjectionDisplay.java as an example.
1 Transform all lat/long coordinates to the projection (forward transform) and resample the data to the projection grid (in "projection space") 2 Transform the projection grid to lat/lon (inverse transform) and resample the data to this transformed projection grid (in "lat/lon space") If someone has some input to this and/or to how to resample most effective I will be happy.
If this is for display purposes, I would suggest creating a Display side CoordinateSystem like in MapProjectionDisplay. The example uses the GRIBCoordinateSystem that Tom W mentioned in his note.
As I am using GRIB data and have a Java GRIB reader (JGrib of course, look at sourceforge), I would like to know how to make a "GRIB adapter". Does anyone have input to this?
I know Richard Gonzales has been in touch with you about mods to JGrib. He was using this to get data into the Integrated Data Viewer (IDV) which takes the GRIB data and transforms it into VisAD fields. He took a roundabout way (on my poor advice), but we will be looking into doing this more efficiently and would love to work with you on this. For each GRIB message, you would need to create a domain set of (row, col) or (lat, lon) from the GDS section of the GRIB message. This would be the domain of the FlatField. If the domain was (row, col), you could use a GRIBCoordinateSystem with it to transform to lat/lon. GRIBCoordinateSystem could be enhanced to support more GRIB projections if needed. The range values for your FlatField would be the decoded values from the field in the GRIB message. Since you would also want to have the level information, you could create Tuple with (level, FlatField). Alternatively, you could build up a 3D FieldImpl of (row, col, z) or (lat, lon, alt) and for each GRIB message that is part of this 3D field, you could set the samples in the 3D space according to the values in the GRIB message. The best structure will depend on your needs. Don ************************************************************* Don Murray UCAR Unidata Program dmurray@xxxxxxxxxxxxxxxx P.O. Box 3000 (303) 497-8628 Boulder, CO 80307 http://www.unidata.ucar.edu/staff/donm *************************************************************
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