[Qgis-developer] geotiff export using print composer

[SBL]

Dear all

For the GarminCustomMap plugin I use the print composer (through python) to
export a (high resolution) geotiff.

Because the mapRenderer does not fill the entire paper in the composer
(although the paper size is set according to the mapRenderer size), there is
a reasonable offset / displacement of the resulting geotiff when using the
output of the print composer directly in combination with the coordinates of
the mapRenderer.

In a workaround I managed to improve the precision of the georeferencing by
removing the empty cells around the mapRenderer (remove cells starting from
bottom / right border, until the black/grey pixels of border line of the
mapRenderer are reached). See code here: 
http://hub.qgis.org/projects/garmincustommap/repository
http://hub.qgis.org/projects/garmincustommap/repository 

This approach has (mainly) three backdraws:
1) The border is not always rendered identically. E.g. the color (which is
used to identify the border line) can vary depending on the color of nearby
objects in the map (border gets grey when there are no objects close to the
border).
2) Depending on the output DPI the number of pixels in the border lines
varys, resulting in less precision in georeferencing with increased output
DPI.
3) The resulting image has a black borderline which can be disturbing when
geotifs are exported as tiles...

My question is now: do you have any suggestions for tackling these issues?
Solutions I`ld very much appreciate are (starting with the favourits):
1) Make the mapRenderer rectangle cover the entire paper in the composer
(with exactly matching corners). (Any Ideas how to do that?)
2) Having the border of the mapRenderer rendered always in 100% black and
with a fixed number of pixels (regardless output DPI). Are there any
possibilities to define this in the settings for the composer/mapRenderer?
3) Having the border of the mapRenderer rendered always in 100% black and
with the number of pixels in a fixed relation to the output DPI. Would it be
possible to define that?

Thanks for helping!

Cheers
Stefan



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