[Mapserver-users] Enhancement for tiling files in multiple coordinate systems
Brent Fraser
bfraser at geoanalytic.com
Fri Apr 25 13:49:35 EDT 2003
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Mapserver users,
I've got about 4 gb of U.S. topos (1:250k scale DRGs) . My goal is to =
serve up the DRGs as one layer and have Mapserver reproject them on the =
fly when necessary to the UTM zone used for viewing (I'll be using =
scripting to determine which UTM zone to use for the user's current =
extent every time they pan or zoom). Usually no reprojection will be =
required except when the user's extent is at the edge of a UTM zone. My =
plan is to use the TILEINDEX feature to reference the raster data. =
Currently Mapserver requires the TILEINDEX shapefile to be in the same =
coordinate system as the data it references.
One option, given the current capabilities of Mapserver, is to have =
one layer for each UTM zone. In the U.S. that would mean about 10 layer =
definitions, not too bad but I may eventually have some other data =
covering 16 zones (or all 60!). Too many layer definitions would be a =
maintenance problem I'd like to avoid.
Another option would be to pre-condition the raster data by =
reprojecting it to geographic coordinates. This would allow one =
tileindex file and therefore one layer definition. But the result is =
that the raster data would always be re-projected on the fly by =
Mapserver (since the display projection would be UTM) and performance =
would suffer.
A solution might be enhance Mapserver to allow the tileindex shapefile =
to be in geographic coords while using the "PROJECTION AUTO" feature to =
determine the coordinate system of the data file. That would require =
two projection definitions in one layer: one for the tileindex =
(proj=3Dlatlong) and one for the data (AUTO) requiring either a change =
to structure of the map file or the addition of keywords. How about =
replacing TILEINDEX and TILEITEM with a TILE object containing INDEX, =
ITEM, and PROJECTION? Any other ideas?
Thanks!
Brent Fraser
GeoAnalytic Inc.
Tel:(403) 213-2700
bfraser at geoanalytic.com
www.geoanalytic.com
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<DIV><FONT face=3DArial size=3D2>Mapserver users,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2> I've got about 4 gb of U.S. =
topos (1:250k=20
scale DRGs) . My goal is to serve up the DRGs as one layer =
and have=20
Mapserver reproject them on the fly when necessary to the UTM zone used =
for=20
viewing (I'll be using scripting to determine which UTM zone to use for =
the=20
user's current extent every time they pan or zoom). Usually no=20
reprojection will be required except when the user's extent is at the =
edge of a=20
UTM zone. My plan is to use the TILEINDEX feature to reference the =
raster=20
data. Currently Mapserver requires the TILEINDEX shapefile to be in the =
same=20
coordinate system as the data it references.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2> One option, given the current =
capabilities=20
of Mapserver, is to have one layer for each UTM zone. In the U.S. =
that=20
would mean about 10 layer definitions, not too bad but I may eventually =
have=20
some other data covering 16 zones (or all 60!). Too many layer =
definitions=20
would be a maintenance problem I'd like to avoid.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2> Another option would =
be to=20
pre-condition the raster data by reprojecting it to geographic=20
coordinates. This would allow one tileindex file and therefore one =
layer=20
definition. But the result is that the raster data would always be =
re-projected on the fly by Mapserver (since the display projection would =
be UTM)=20
and performance would suffer.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2> A solution might be enhance =
Mapserver to=20
allow the tileindex shapefile to be in geographic coords while using the =
"PROJECTION AUTO" feature to determine the coordinate system of the data =
file. That would require two projection definitions in one layer: =
one for=20
the tileindex (proj=3Dlatlong) and one for the data (AUTO) =
requiring either a=20
change to structure of the map file or the addition of =
keywords. How=20
about replacing TILEINDEX and TILEITEM with a TILE =
object containing INDEX,=20
ITEM, and PROJECTION? Any other ideas?</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Thanks!</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Brent Fraser</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>GeoAnalytic Inc.<BR>Tel:(403) =
213-2700<BR><A=20
href=3D"mailto:bfraser at geoanalytic.com">bfraser at geoanalytic.com</A><BR><A=
=20
href=3D"http://www.geoanalytic.com">www.geoanalytic.com</A></FONT></DIV><=
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