[Qgis-developer] Inconsistent display of a selected simple outline polygon

[Giovanni Manghi]

Hi Richard,


> Hi Ramon,
> 
> I saw there is some discussion going on about how to show or not show
> selections of polygons also in an issue: http://hub.qgis.org/issues/4553

> 
> Somebody aware of the way other desktop gis applications are handling this?


I made a few tests comparing how the selection works in qgis, gvsig and
udig for overlapped/partially overlapped polygons with fill/partial
transparency/no fill.

I attached a few screenshots in the above ticket.

Solid fill: 

The "Select single feature" tool in QGIS the tool does exactly what is
expected, it selects only (one) clicked feature. If one polygon is
completely *above* another one, then clicking on it causes qgis to
select just it. The same (obviously) if clicking on a polygon in an
point that is above another one that is partially overlapped.

In gvSIG and uDIG the "Select feature at point" tool works in a slightly
different way, selecting also what is under the selection spot, like the
"select features by..." tool in QGIS.

In QGIS and gvSIG if a polygon is completely overlapped and *under*
another one, there is no way to *) immediately understand is there,
looking at the canvas *) select only the underlying polygon (for example
from the attribute table) and have the selection color pop-up, because
it is always covered by the above polygon fill/selection color.

On the other hand uDIG behave nicely by using a default transparency
level for both the fills (when adding a vector) and the selection color,
so the user can immediately see if there are overlapped polygons and
also can see if/when there is a selected polygon under another one. This
would be a nice option in the QGIS general Options menu (using a default
transparency level for fills and selection color).

uDIG has also another nice feature: it makes border width of selected
objects bigger of the unselected ones. This is very handy especially
when it is used no fill for polygons.



Semi-transparent fill: 

In QGIS and gvSIG doesn't change much compared with the solid fill. The
selection color is solid so if two overlapping polygons are selected
only the above one is visible. If only the underlying one is selected
(from the table of attributes) it is visible because the above polygon
does not have a solid color.

uDIG as it uses by default semi-transparent selection color so it is
same as when using solid fills.



No fill:

In QGIS and gvSIG doesn't change much beside one important case: with
two overlapping polygons, with the smaller one completely above the
other, when selecting *just* the underlying one the selection color
"fills" also the above one, and the user can say how many polygons are
selected only if he/she looks in the attribute table.

In uDIG it happens the same BUT as the border width of selected objects
is bigger than unselected ones, the user knows what is selected and what
is not by just looking at the map canvas. This seems to me a really nice
feature.



There are also a few differences when it comes to editing polygons under
other ones.

In QGIS if using the solid fill or when the above is selected, it is not
possible to see the borders of the polygon being edited, just the nodes
highlighted by the node tool.

in gvSIG when clicking with a edit tool in a spot that is over two
overlapping polygons it pop-up a windows to let the user choose what to
edit, if the above or the underlying geometry. Once selected the polygon
being edited is also given a new color.

In uDIG the fill color of the polygon being edited is removed (as also
for the above one) and instead is given the semi-transparent selection
color.


cheers

-- Giovanni --