[mapserver-dev] Using mapserver.a to generate tiles

[Stephen Woodbridge]

Hi all,

I guess these questions might be targeted at Steve L and/or Thomas 
Bonfort, but I'll take info from anyone that might know.

I have written a C program that uses mapserver.a and generates tiles for 
seeding a tile cache. It works great with GD and AGG rendering when I 
quantize the output images as 8-bit png images that can be transparent 
or not.

I have run into two problems:

Rendering transparent overlays with AGG and then palettizing the image 
leaves dark pixels along the lines as an artifact of the anti aliasing 
and the palettization. But I can chop these meta tiles into tiles with 
no problems.

If I try to generate RGBA tiles, these artifacts are not seen in the 
meta tile if I leave the image as RGBA, but when I chop the metatile 
into tiles the background is no longer transparent (I'm guessing it is 
RGB and not RGBA.

The code makes calls like these:

// read the mapfile, and setup the layers, extents, outputformat, then
oImg = msDrawMap(map, MS_FALSE);

// save the image to force color reduction
// for the RGBA case ie: not palettized
// this appears to change  buffer_format = 7 to buffer_format = 1
ret = msSaveImage(NULL, oImg, szMetaImg);

// we cycle through the rows, cols of the metatile write the tiles
oTile = msImageCreateGD(tileWidth, tileHeight, oImg->format, NULL, NULL, 
map->resolution, map->defresolution);

msImageCopyMerge(oTile, oImg, 0, 0, tileLeft, tileTop, tileWidth, 
tileHeight, 100);

ret = msSaveImage(NULL, oTile, qtp);
msFreeImage(oTile);


So, I'm guessing that the change in buffer_format is somehow affecting 
the behavior of msImageCreateGD() or msImageCopyMerge() that is 
affecting the alpha transparency when I create the tiles. Can anyone 
shed some light on that and how I might work around that.

Second, since the RGBA tile issue was an attempt to work around the dark 
speck artifacts on the anti aliased lines that get palleted, any 
thoughts on how to remove the specks.

Third, but less important at the moment, I am aware this all changes in 
6.0 and I am curious about what happens when the GD code is removed. But 
I can probably wait till that is in trunk and go digging after that.

My mapfile looks like the following. I have tried various combinations 
of options on the various OUTPUTFORMATs.

-Steve W

MAP
   NAME "Statesp020"
   EXTENT -19941038.1 1999506.7 20013931.8 11539767.3
   SIZE 700 550
   SHAPEPATH "/u/data/flytecomm/gisdata/"
   #SYMBOLSET "/u/data/maps/symbols/symbols.sym"
   #FONTSET "/u/data/maps/fontset.txt"
   IMAGECOLOR 0 0 0
# IMAGETYPE 'agg_qn' # this leaves artifacts along the lines
# IMAGETYPE 'PNG8'   # no artifacts but lines are not anti aliased
# IMAGETYPE 'agg_32png' # metatile is ok, tiles have black bgcolor
   IMAGETYPE 'agg_32png' # tile are not transparent
   TRANSPARENT ON
   UNITS METERS
#  DEBUG 5
#  CONFIG MS_EEORFILE "stderr"

   OUTPUTFORMAT
     NAME "agg_qn"
     DRIVER "AGG/PNG"
     EXTENSION "png"
     MIMETYPE "image/png"
     IMAGEMODE RGBA
     TRANSPARENT ON
     FORMATOPTION "INTERLACE=false"
     FORMATOPTION "QUANTIZE_NEW=ON"
     FORMATOPTION "QUANTIZE_FORCE=ON"
     FORMATOPTION "QUANTIZE_DITHER=OFF"
     FORMATOPTION "QUANTIZE_COLORS=256"
     FORMATOPTION "TRANSPARENT=ON"
   END

   OUTPUTFORMAT
     NAME "agg_32png"
     DRIVER "AGG/PNG"
     EXTENSION "png"
     MIMETYPE "image/png"
     IMAGEMODE RGBA
     TRANSPARENT ON                # comment or not does not help
     FORMATOPTION "INTERLACE=OFF"
     FORMATOPTION "TRANSPARENT=ON" # comment or not does not help
   END

   OUTPUTFORMAT
     NAME PNG8
     DRIVER "GD/PNG"
     EXTENSION "png"
     MIMETYPE "image/png"
     IMAGEMODE RGBA
     TRANSPARENT ON
     FORMATOPTION "INTERLACE=false"
     FORMATOPTION "QUANTIZE_NEW=ON"
     FORMATOPTION "QUANTIZE_FORCE=ON"
     FORMATOPTION "QUANTIZE_DITHER=OFF"
     FORMATOPTION "QUANTIZE_COLORS=256"
     FORMATOPTION "TRANSPARENT=ON"
   END

#  PROJECTION
#    # Sperical Mercator
#    "+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

   SYMBOL
     NAME 'circle'
     TYPE ELLIPSE
     POINTS 1 1 END
     FILLED true
   END

   LAYER
     NAME "states"
     TYPE POLYGON
     STATUS DEFAULT
     TRANSPARENCY ALPHA
     DATA "states/statesp020-900913"
     CLASS
       STYLE
         WIDTH 1.0
         #SIZE 3.0
         #SYMBOL 'circle'
         #COLOR "#b5d29c"
         OUTLINECOLOR "#88ff88"
       END
     END
   END

END