Opened 13 years ago
Last modified 13 years ago
#4035 new defect
Data drops out of view when source data are lon/lat and display is polar projection
Reported by: | bruceraup | Owned by: | warmerdam |
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Priority: | normal | Milestone: | |
Component: | MapServer C Library | Version: | unspecified |
Severity: | normal | Keywords: | |
Cc: | sdlime |
Description
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.