On 25.06.2011 10:21, Michaël Michaud wrote:
> I have just tested geomconv for the first time. Good work.
> Geometry type conversion is a very useful feature.
> I agree with peppe that it would be nice to have the menu in layerview
> context menu
thanks, and thanks for all the issues you pointed out. i highly value that!
this is terribly needed because my gis background is purely theoretical and
limited to my work on openjump.
> In my opinion, it would need a bit more work (and translation).
> I would vote to include it in 1.4.2 (and I'm ready to help to improve and to
> translate it).
no problem. i'll keep it external until we all agree it is matured enough. any
other distro can use the plugins as well packaged as extension.
> Here are my remarks (more or less important, feedback is welcome) :
>
> 1) It took me some times to understand the differences with existing tools
> like extract points
> I would reorganize Edit Geometry convert menu into
> - Edit Geometry > Extract (points, boundaries, segments...)
> these plugins work on a whole layer and create a new one for the result
> - Edit Geometry > Convert (ede's conversion tool)
> these plugins work mainly on a selection and modify directly geometries
Polygonize is also a conversion tool (but i can't be put in the same category
as it works totally different)
Planar Graph is also extractionary?
> Note : conversion are undoable, which is a great feature !
and necessary, because errors might have occured and the user might not be
satidfied with the result
we should by the way consider a empty undo/redo queue functionality (with
button) to release ram after big conversions. is there something similar
already existing?
> 2) If no feature is selected, the tool converts the whole layer
> This is a useful feature, but It would be nice to warn the user, as the menu
> name is convert "selected" geometry
well it is 'Convert selected Geometries/Layers to' exactly, but you are right a
short modal ok/cancel dialogue is in order.
> 3) Converting polygons with holes or multipolygons into linestrings create
> bridges joining linear components
> It should be converted int multilinestrings
> Why not use *com.vividsolutions.jts.geom.util.LinearComponentExtracter*
good hint, will check out LinearComponentExtracter for a conversion to
Multilinestring. if the user explicitly ordered a conversion to Linestring it
behaves correctly, don't you think?
> In a more general way, I would propose to convert geometries into :
> - ponctual, lineal or polygonal geometries
i am not sure if i really want to spend effort to make it that 'intelligent'.
> The plugin should choose the best geometry type
> - points into punctual -> points
> - any other geometry into punctual -> multipoint
> - point into lineal : not possible
> - multipoint into lineal -> linestring (or linearring if first = last
> coordinate)
> - linestring into lineal -> linestring
> - polygon without hole into lineal -> linear ring
> - polygon with holes or multipolygons into lineal -> multilinestring
> - point into polygonal -> not possible
> - linestring into polygonal -> polygon if closed (option to close it ?)
> - multilinestring into polygon -> polygon or multipolygon (may be difficlut
> to find interior rings and exterior rings, I have some code for that)
i rather prefer the user to exactly specify what the result should be. this way
the user can e.g. make point to linestring and add more points to the same
feature. the user retains pretty much has the possibility to convert anything
to everything (if possible).
if there i enhanced logic i'd rather offer conversion targets like 'linearring
(autoclose ring)' or 'multilinestring (separate holes)'
> 4) Missing coversion of polygons with holes and multi-polygons into
> multilinestring
this should come with the multilinestring (separate holes) target provided i
find the logic somewhere that does that (will check your suggestion above). the
standard conversion to multi* will create a multi* with one entry.
> Possible improvements :
>
> 5) The tool works on a per feature basis. It means that a "linestring" cannot
> be converted into a "point". It may be useful, but it is not always
> intuitive. I would like an option like "authorize conversion of one feature
> into several". Just an idea for improvement, not a requirement.
i'd really like to stick with the per feature basis for now. let's solve the
outstanding issues and we might think about splitting fatures.
> If neither a multipoint nor a linestring, nor a polygon can be converted to a
> point ("Too many points selected. Only one point needed") what can the
> "convert to point" plugin do ?
exactly what is possible. convert a multipoint, a linestring or a polygon with
exactly one point to a point geometry ;).
> 6) Converting linearring into multipoints keeps the starting and the ending
> point (it's OK as the default behaviour, but an option as the one in extract
> points would be welcome)
you mean deleting the useless end point? how about a multipoint (remove
doubles)?
> Converting multipoints into linear ring fails if last point is not equals to
> first one (it's OK as the default behaviour, but an option to close the line
> would be welcome)
target 'linearring (autoclose ring)' as suggested above?
>
> 7) Missing conversion of multi linear rings into polygons or multi-polygons
> (not easy)
why is it difficult
MultiLinearring to MultiPolygon should be easy
MultiLinearring to Polygon depends on the validity of the resulting polygon
(all coordinates together in the order of the source geometries).
>
> Hope it helps
>
lots :) .. thanks again, ede
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