Re: Raster Layer is Clipped

> 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
>>

>>
>> 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.
>