[mapserver-users] projection weirdness php_mapscript vs. mapserver itself

[Alexander Mayrhofer]

Hi,

I've found a projection weirdness in php_mapscript vs. Mapserver, and
i'd appreciate any hint (i'm pretty desperate already :-/ )..

i'm using php_mapscript to load a mapfile, and put a marker on the map.
The map (and background raster) is in the (in)famous "Google"
projection, while marker data is in WGS84.

During debugging i noticed that using the _same_ coordinates and
projection, i get two different marker positions on the map, depending
whether i reproject the marker "manually" using php_mapscript or
via Mapserver itself...

The attached example (also available at
http://map.timatio.com/trace_icon_32.87_9.33_260x150_TEST.jpg ) shows
the problem - the "upper" marker is reprojected using Mapserver, and the
"lower" using php_mapscript, even though they use the same coordinates 
and projection. The further away from the equator, the
larger the offset becomes (you can play around with the lat/long
parameters after "_icon_" in the above URL).

The respective lines of code look like this (i _think_ the projection is
absolutely identical for both cases - compare the mapscript lines with
the mapfile below..):

      // manual reprojection - weirdness avoidance
      $in_proj = ms_newProjectionObj("proj=longlat, ellps=WGS84,
datum=WGS84, no_defs");
      $out_proj = ms_newProjectionObj("proj=merc, a=6378137, b=6378137,
lat_ts=0.0, lon_0=0.0, x_0=0.0, y_0=0, k=1.0, units=m, nadgrids=@null,
no_defs");
      $centerpoint = ms_newPointObj();
      $centerpoint->setXY($args['lon'], $args['lat']);
      $centerpoint->project($in_proj, $out_proj);

      ...

      // set marker in "manually" projected layer
      $center_layer = $map->getLayerByName("center");
      $point = ms_newPointObj();
      $point->setXY($centerpoint->x, $centerpoint->y);
      $line = ms_newLineObj();
      $line->add($point);
      $shp = ms_newShapeObj(MS_SHAPE_POINT);
      $shp->add($line);
      $center_layer->addFeature($shp);

      // set marker for "mapserver projected" layer
      $centertest_layer = $map->getLayerByName("centertest");
      $pointtest = ms_newPointObj();
      $pointtest->setXY($args['lon'], $args['lat']);
      $linetest = ms_newLineObj();
      $linetest->add($pointtest);
      $shptest = ms_newShapeObj(MS_SHAPE_POINT);
      $shptest->add($linetest);
      $centertest_layer->addFeature($shptest);

And the mapfile looks like this:

#
# Start of map file
#

NAME micromap
STATUS ON
SIZE 176 116
UNITS meters
DEBUG ON
OUTPUTFORMAT
    NAME jpeg
    FORMATOPTION "QUALITY=95"
    FORMATOPTION "INTERLACE=OFF"
    DRIVER "GD/JPEG"
END
PROJECTION
    "proj=merc"
    "a=6378137"
    "b=6378137"
    "lat_ts=0.0"
    "lon_0=0.0"
    "x_0=0.0"
    "y_0=0"
    "k=1.0"
    "units=m"
    "nadgrids=@null"
    "no_defs"
END
EXTENT -300000 -200000 300000 200000
SHAPEPATH "/data/gis/NE2/"
IMAGECOLOR 204 221 238
IMAGETYPE png24

FONTSET /data/gis/brd/fonts.list

SYMBOL
    NAME "punkterl"
    TYPE PIXMAP
    IMAGE assets/punkterl.png
LAYER
    NAME "NE2_modis3"
    STATUS ON
    TILEINDEX "/data/gis/NE2/NE2-modis3-tileindex.shp"
    TILEITEM "Location"
    TYPE RASTER
END

LAYER
    NAME "centertest"
    STATUS on
    TYPE point
    TRANSFORM true
    POSTLABELCACHE true
    PROJECTION
      "proj=latlong"
      "datum=WGS84"
      "ellps=WGS84"
      "no_defs"
    END
    CLASS
      STYLE
        SYMBOL "punkterl"
      END
      LABEL
        ANGLE 0
        SIZE 9
        COLOR 0 0 0
        TYPE truetype
        FONT dejavu
        POSITION uc
        OFFSET 0 2
        FORCE true
        BUFFER 3
        MINFEATURESIZE 10
      END
    END
    TRANSPARENCY alpha
END

LAYER
    NAME "center"
    STATUS on
    TYPE point
    TRANSFORM true
    POSTLABELCACHE true
    CLASS
      STYLE
        SYMBOL "punkterl"
      END
      LABEL
        ANGLE 0
        SIZE 9
        COLOR 0 0 0
        TYPE truetype
        FONT dejavu
        POSITION uc
        OFFSET 0 2
        FORCE true
        BUFFER 3
        MINFEATURESIZE 10
      END
    END
    TRANSPARENCY alpha
END

END


Notice that the projection is (imho) absolutely identical - The
"correct" reprojection seems to be the "manual" reprojection - it aligns
with the background map that was reprojected with gdalwarp...

Mapserver version is 4.10, proj version is 4.4.9d-2 - I do appreciate
any hints on what i could be doing wrong..

thanks,

Alex

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