Re: [Qgis-developer] some flaw in RDP algorithm?
Hi Giuliano, > > > you're probably right, but I have never advised to develop a new > simplification algorithm :-) > > I am a "mathematical" as a hobby, I have only met a "little problem" > with the RDP algorithm and I reported it, and I had fun writing an > algorithm for fun but no idea of proposing developments in this > direction; > > Ah, I missed that. If it's a new algorithm, maybe try and get it published into a journal? Then other math types who are into that sort of thing (and more importantly, understand it! :-) ) can give you feedback on it. As you may know, there's quite a bit of literature on generalisation/simplification algorithms, including for RDP - http://scholar.google.co.uk/scholar?q=rdp+simplification - you may find some of that interesting reading. Kind Regards, Jonathan -- This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [Qgis-developer] some flaw in RDP algorithm?
Il giorno Wed, 5 Feb 2014 11:31:25 + Jonathan Moules ha scritto: > Hi, hi Jonathan, > QGIS already has access to tons of generalisation options via the > grass v.generalise tool > > . > > Is there a reason those can't be used? I wonder how many > implementations of Douglas Peucker QGIS already has? Re-implementing > other ones when they already exist doesn't seem optimal.. you're probably right, but I have never advised to develop a new simplification algorithm :-) I am a "mathematical" as a hobby, I have only met a "little problem" with the RDP algorithm and I reported it, and I had fun writing an algorithm for fun but no idea of proposing developments in this direction; > > http://grass.osgeo.org/grass64/manuals/v.generalize.html thank you for your report, we'll take a look soon as I can; > Cheers, > Jonathan thanks, best regards, sfm(+Gt)be, giuliano curti ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [Qgis-developer] some flaw in RDP algorithm?
Hi, QGIS already has access to tons of generalisation options via the grass v.generalise tool http://grass.osgeo.org/grass64/manuals/v.generalize.html Split into four categeories - Generalisation, Smoothing, Displacement, Network Generalisation. Is there a reason those can't be used? I wonder how many implementations of Douglas Peucker QGIS already has? Re-implementing other ones when they already exist doesn't seem optimal. Of course maybe you want a new one, but then I'd suggest maybe it could be added to Grass and that in turn would automatically feed into QGIS. Cheers, Jonathan On 3 February 2014 14:29, kimaidou wrote: > Hi, > > We definitely need a better simplify algo in QGIS than Douglas Peucker. It > is very fast, but does not really preserve the "shape" of polygons/lines > and does not preserve topology. Your work seems interesting. Is you > approach similar to Visvalingam algo (used for example in Mapshaper : > http://mapshaper.org/ ) ? Does it preserve topology ? > Having a simplifier that can preserver topology while being fast like > Visvalingam would be great indeed ! > > ps: sorry to bring personnal will in response of your topic instead of > really answering your question.. > > Michael > > > 2014-02-03 giulianc51 : > > Hi all, >> >> >> I do not know if this is the right place to talk about it but I think I >> have found a small problem in the plugin fTools, particularly in the >> "Simplify geometry" of the module "Geometry tool"; >> >> more precisely, the problem is in the RDP algorithm used by the >> function; >> >> nothing dramatic, the procedure works properly and provides a >> simplified line, but I have isolated some cases in which the solution >> is not optimal: some points, not needed for the definition of the line, >> are left; >> >> to sum up, I put some considerations in some slides here >> http://www.slideshare.net/giulianc/clean-lines-presentation; >> >> can you tell me where and how it can be of interest to discuss this >> topic? >> >> thanks, best regards, sfm+Gtbe(*) :-) >> giuliano curti >> >> >> (*) sorry for my (+ Google translation) bad english :-) >> ___ >> Qgis-developer mailing list >> Qgis-developer@lists.osgeo.org >> http://lists.osgeo.org/mailman/listinfo/qgis-developer >> > > > ___ > Qgis-developer mailing list > Qgis-developer@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-developer > -- This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
Re: [Qgis-developer] some flaw in RDP algorithm?
Hi, We definitely need a better simplify algo in QGIS than Douglas Peucker. It is very fast, but does not really preserve the "shape" of polygons/lines and does not preserve topology. Your work seems interesting. Is you approach similar to Visvalingam algo (used for example in Mapshaper : http://mapshaper.org/ ) ? Does it preserve topology ? Having a simplifier that can preserver topology while being fast like Visvalingam would be great indeed ! ps: sorry to bring personnal will in response of your topic instead of really answering your question.. Michael 2014-02-03 giulianc51 : > Hi all, > > > I do not know if this is the right place to talk about it but I think I > have found a small problem in the plugin fTools, particularly in the > "Simplify geometry" of the module "Geometry tool"; > > more precisely, the problem is in the RDP algorithm used by the > function; > > nothing dramatic, the procedure works properly and provides a > simplified line, but I have isolated some cases in which the solution > is not optimal: some points, not needed for the definition of the line, > are left; > > to sum up, I put some considerations in some slides here > http://www.slideshare.net/giulianc/clean-lines-presentation; > > can you tell me where and how it can be of interest to discuss this > topic? > > thanks, best regards, sfm+Gtbe(*) :-) > giuliano curti > > > (*) sorry for my (+ Google translation) bad english :-) > ___ > Qgis-developer mailing list > Qgis-developer@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-developer > ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
[Qgis-developer] some flaw in RDP algorithm?
Hi all, I do not know if this is the right place to talk about it but I think I have found a small problem in the plugin fTools, particularly in the "Simplify geometry" of the module "Geometry tool"; more precisely, the problem is in the RDP algorithm used by the function; nothing dramatic, the procedure works properly and provides a simplified line, but I have isolated some cases in which the solution is not optimal: some points, not needed for the definition of the line, are left; to sum up, I put some considerations in some slides here http://www.slideshare.net/giulianc/clean-lines-presentation; can you tell me where and how it can be of interest to discuss this topic? thanks, best regards, sfm+Gtbe(*) :-) giuliano curti (*) sorry for my (+ Google translation) bad english :-) ___ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
