Questions about extents and projections

Brian Peschel brianp at OCCINC.COM
Tue Jan 31 16:33:15 EST 2006

I have taking the 4.6.2 version of MapServer and (using the makefile)
building as a C library and linking into a custom application I have.  I am
using the MapServer code to generate JPG images.

I am trying to create a cube of images that I can then stitch together.
Something like:

Every image should have the same number of pixels, so I am overriding the
map file by resetting the value in the loaded mapObj ojbect by:
map->height = 354;
map->width = 609;
I know the lat/lons of every corner of each image, so I am overriding the
map file by resetting the extent in the loaded mapObj object by:
map->extent.minx = corner[SW].x();
map->extent.maxx = corner[SE].x();
map->extent.miny = corner[NW].y();
map->extent.maxy = corner[SW].y();

I then create the 9 images.  If I then paste the 9 images together I would
expect a seamless connection (labels might be messed up).  I am not seeing
this.  The stitching is working on the same row.  A + B + C looks good, D +
E + F looks good and G + H + I looks good.  Hoever the columns are wrong.  A
+ D + G has overlap on the top an bottom of the image.

I used to do this manually (using GD) by converting the lat/lon coordinates
to pixels and calling GD methods to draw lines.  Comparing my older images
to the new MapServer images, it looks like the image is being stretched in
both Y directions (miny and maxy are both changing).

Based on the tutorial I worked through and O'Reily's book, I expected the
features draw to be 'stretched' to match the number of pixels I requested.
I at least expected one of the y values to be correct, not both of them.

Any ideas here?  I am not actually using any projection in my map file.  I
am requesting lat/lon in the same projection a the shp file.  There are no
PROJECTION blocks in my map file at all.

I can provide a copy of my map file and C code if it will help.  I can also
provide a image of the stiched images.

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