Data drops out of view when source data are lon/lat and display is polar projection

[mapserver-bot]

Reporter: bruceraup
Date: 2011/09/28 - 06:14
Trac URL: http://trac.osgeo.org/mapserver/ticket/4035
Frank Warmerdam and I have discussed this a few times: when lon/lat data are stored in a database and the MapServer application is displaying in a polar projection (e.g. polar stereographic), when the viewport or a selection window contains the pole, the vertices of the viewport are transformed to lon/lat, then an intersection is done in the DB using the transformed box. But in lon/lat space, this "box" can look more like an annulus, and so data in the hole of the donut drops out. This is illustrated at

http://spot.colorado.edu/~braup/MapServer/

Frank and I discussed a possible solution where MapServer would detect when a pole is within the selection box or viewport, and then break that box into four pieces using two orthogonal cuts through the pole. Vertices might have to be added to each edge before transformation as well, to maintain the integrity of the shape of the selection box.

Note that this would apply to any data store -- not just PostGIS.

I am adding this ticket on Frank's request, after discussion at FOSS4G 2011 in Denver.

[mapserver-bot]

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This issue has been closed due to lack of activity. This doesn't mean the issue is invalid, it simply got no attention within the last year. Please reopen with missing/relevant information if still valid.

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