[Mapserver-users] Enhancement for tiling files in multiple coordinate systems

Fri Apr 25 10:49:35 PDT 2003

This is a multi-part message in MIME format.

------=_NextPart_000_019F_01C30B20.BE7F2B10
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

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

------=_NextPart_000_019F_01C30B20.BE7F2B10
Content-Type: text/html;
	charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Diso-8859-1">
<META content=3D"MSHTML 6.00.2600.0" name=3DGENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<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><=
/BODY></HTML>

------=_NextPart_000_019F_01C30B20.BE7F2B10--