[Qgis-developer] Known problems with QGIS

Agustin Lobo alobolistas at gmail.com
Mon Jan 31 15:27:22 EST 2011

Hi all,

After an intensive use of QGIS 1.6 (binary installations on linux, MAC
and windows), I've found the
following problems to be of particular operational concern:
1. Histogram tool for raster layers: I think it only works right for
Unsigned Byte images, for sure it is wrong if negative values are
present and it is always
a poor graphic. The histogram is essential for a sounded stretching
(which in turn is essential for good display) and important to
understand the distribution of the variable, the presence of outliers
2.While 1-Band Raster Color band and Colour Scale Bar go in the right
direction, these type of tools must be integrated in the Properties
dialog. A reasonable key color table should show up by default and
raster layers of qualitative variables (i.e. land cover maps) should
have appropriate tools for being displayed.
3. Vector operations are too slow as soon as layers are moderately complex.
4. Tools for the display of quantitative fields is still insufficient.
Quantiles, natural breaks etc should show on a histogram and the user
should be able of, at least, setting the meaningful min and max values
(these algorithms fail in the presence of outliers) and best being
able to apply interactive fine tuning. Some transformations (i.e.
logarithmic) should be possible without having to actually calculate
the new field.
5. Point sampling tool: this tool should join the attribute table (or
let the user select which fields to keep, or at least keep an ID
field) of the original points layer with the one(s) of the layer(s)
from which the values are to be extracted. Currently the user has to
create an ID for the original point layer and for the resulting  point
layer and then run a join operation (3 more operations). Point
sampling tool is very important to merge information between vector
and raster layers for further analysis.
6. QGIS crashed from time to time (sometimes calculating the
histogram). As crashes were suffered by inexperienced users, I've not
been able to collect detailed information.

RasterCalc has performed very well and has been very useful for
students to understand spectral vegetation indices. An if() operation
is missing but is coming...

I think all these issues have filled tickets, but wanted to list them
together. As browsing the ticket system is kind of complex for
potential new users, we should include a list of Known Problems
including the most important ones in each release. QGIS is good, no
need to hide problems.
Hopefully some of the listed problems will be addressed during the
next hackfest and hopefully I'll be able to attend to help out

Thank you all for your work.


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