Re: Raster Layer is Clipped

> Jon Burgess wrote:
> > On Sun, 2009-06-21 at 11:28 -0700, Andrew Ayre wrote:
> >> I've given up on trying to compile pgsql2sqlite for now and instead made
> >> some progress on using a georeferenced layer using Gdal. However it
> >> seems that Mapnik is clipping the image even though I have set the map
> >> size to the size of the bitmap and used the bitmap envelope.
> >>
> >> Here are my input files:
> >>
> >> http://files.britishideas.com/public/mapping/osmgeoref.png
> >> http://files.britishideas.com/public/mapping/osmgeoref.pgw
> >>
> [snipped]
> >>
> >> And here is the output with the top and bottom of the input PNG missing:
> >>
> >> http://files.britishideas.com/public/mapping/demo.png
> >>
> >> For completeness here is the output XML file:
> >>
> >> http://files.britishideas.com/public/mapping/map.xml
> >>
> >> I used red as a background colour to highlight the issue. Any ideas what
> >>   I am doing wrong? I'm sure I'm overlooking something silly.
> >
> > I can not explain it particularly clearly, but I believe the problem is
> > that the original image was not created in latlong projection, hence the
> > 800x361 pixels are not square:
> >
> > $ gdalinfo osmgeoref.png
> > Driver: PNG/Portable Network Graphics
> > Files: osmgeoref.png
> > Size is 800, 391
> > Coordinate System is `'
> > Origin = (-110.812896694075803,32.220948081346208)
> > Pixel Size = (0.000037724479586,-0.000031870889024)
> >
> > Notice how the pixel sizes are different in the two dimensions. If you
> > adjust the output bitmap to fit this ratio then you get:
> >
> > 800 * 0.000037724479586 / 0.000031870889024 = 947
> >
> > Then resize the map to this dimension:
> >
> > m = Map(947,391,'+proj=latlong +datum=WGS84')
> >
> > The final output then looks like the original with no clipping.
> >
>
> Hi Jon,
>
> I tried it and the output isn't quite the same as the input. The top of
> the image now matches but the bottom doesn't. Notice the orange road at
> the very bottom of the input image? It's chopped off the output image.