GRAVFFT query/check
Lester Anderson <[email protected]>
| Newsgroups | gmane.comp.gis.gmt.user |
|---|---|
| Message-ID | <[email protected]> |
Hello I just wanted to check the use of gravfft for the Bouguer correction (land and Sea). Windows 7 operation. Under v4 I would split the computation for land/sea and so this would become (under v5): gravfft test_topo.grd -Gtopo_corr_land.grd -D2670 -E6 -V (use land mask -N0/1) gravfft test_bathy.grd -Gtopo_corr_sea.grd -D1640 -E6 -V (use sea mask -N1/0) grdmath free-air.grd topo_corr_land.grd SUB -V = bouguer_land.grd grdmath free-air.grd topo_corr_sea.grd SUB -V = bouguer_sea.grd grdmath bouguer_land.grd bouguer_sea.grd ADD -V = Bouguer_land_sea.grd What I noticed was that, using the land-only grid, the values in the "sea" were say around a near constant -53, when the land mask has the sea set to 0. This would clearly give a wrong value when added to the sea-only data. Clearly, one cannot have NaN values in the grid as the FFT would fail, in fact when tested it caused gravfft to crash. If it is all land or all sea, there is no problem, but how can this be done for a combined region properly? Do I compute the land and sea density grids over the whole area, and then mask the results - just trying to see the logical path here. Under GMT 4 I would simply use grdmath and the mask grids to get the separate files to sum, no issues there. I am sure it is a simple answer (hopefully) Cheers Lester To unsubscribe, send the message "signoff gmt-help" to [email protected]