[Qgis-developer] horizontal lines pdf/ps/image output
andreasplesch at netscape.net
Wed Oct 20 13:33:25 EDT 2010
using qgis (1.5, I believe) to generate a bathymetric map from data
for the Bering Strait, I came across horizontal lines when trying to
output the map in print composer in any way. The process was a good
success in that everything which was needed could be done and the
result was very useful for the biologist who wanted a good looking map
of the "sunken land bridge". There was not anything online. It might
have even been faster than using ArcMap, apart from the issue below.
The map has raster bathymetry with a custom color map, a transparent
grey scale shaded relief on top, and contours. The horizontal lines
show up after I compose a map and then output the map in any way. They
do not show up in the main qgis window or the print compose. They
become more frequent when I increase the resolution to say 600 dpi. At
300 dpi there is just one. At 150 dpi there is none. I believe it
might have to do how images are partitioned into small rectangles, and
perhaps the transparent layer ? Since the output might be managed by
Qt, there may not be a lot of options but it was an important issue.
After all, in the end you need to output.
Another, unrelated issue, with output was that the colors were only
correct in the postscript. In the pdf and image output they were too
dark, perhaps a transparency issue.Also text seemed rasterized when on
top of images.
It was a joy to be able to import easily the ASCII grid, to crop it,
to easily warp it to a suitable projection, to easily generate
contours and shaded relief, and to add some annotation in the print
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