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Maciej Sieczka wrote:
Thanks for your v.in.gshhs GRASS 6 port. I have a problem: when importing full GSHHS extent, strange horizontal lines through the whole longitudal extent are present in the output GRASS vector map, which are *visible only in v.digit or QGIS*, but never on the regular wxGUI map display or X monitors. To reproduce please import e.g. gshhs_c.b, zoom to it in wxGUI, then open in digitizer and compare. Also please notice that *in QGIS those bogus lines are always visible*. I suppose this is related to the GSSHS data extent 0 - 360 vs. GRASS -180 - 180.
Strange. v.in.gshhs converts all lon coordinates to the range of -180 - 180. The only possible problem is Eurasiafrica (also converted to -180 - 180), crossing the datum border, all other shorelines are not crossing the datum border. I wrote the new v.in.gshhs port so that it displays properly, but GRASS latlon handling is not fully consistent, e.g. bounding boxes in vector topology ignore the datum border problems whereas (most?) lib/gis functions take care of that. My guess is that neither the wxGUI vdigit nor QGIS do this on-the-fly wraparound like the GRASS display. No idea how to solve this. Glynn once remarked that he tried to support -360 - 360 in latlon, and said that this opens a problem box of Pandora. I tried myself, and found the same problem box :-(
I personally like the way QGIS or MapServer handles it - they just don't care and don't try to treat lat-long data as connected at the datum border. This has the major plus that in those applications there is no problem with manual browsing/editing world-wide lat-long data. One can pan and zoom just like in any other coordinate system and the display coordinate extent is not restricted. GRASS automatic wrapparound is a feature that brings more troubles than benefits to developers and users IMHO. Maciek -- Maciej Sieczka http://www.sieczka.org _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev
