[Boost.Geometry] - Union generates polygon with punctures
Hello ! I'm trying to use Boost.Geometry library to implement Minkowsky algorithm (i.e. polygon convolution). I try to implement it in the same way Boost.Polygon does, but during the algorithm execution, a boost::geometry::overlay_invalid_input_exception is raised. It seems that one of the input polygons to the union_ function is invalid. To understand my mistake, I outputed the operand polygons to SVG files and I discovered punctures in one of them. I believe Boost.Geometry thinks my polygon is self-intersecting (may be due to precision error with floats ?) - but this polygon itself is the result of a previous union operation. For info, I attached the SVG file (use inkscape to see it completely since segments are out of the box due to negative coordinates). I don't know if solutions to this problem exists or if the library is faulty (the bad polygon is the result of an union operation). One workaround would be to detect punctures and remove them, but it's kind of ugly imho... Some more details: - point coordinates type is float, - I use custom class instead of point_xy model, - polygon winding is counter-clockwise. Thank you in advance for any help, Olivier
Hi, On 3-7-2013 12:22, Olivier Heriveaux wrote:
Hello !
I'm trying to use Boost.Geometry library to implement Minkowsky algorithm (i.e. polygon convolution). I try to implement it in the same way Boost.Polygon does, but during the algorithm execution, a boost::geometry::overlay_invalid_input_exception is raised.
It seems that one of the input polygons to the union_ function is invalid. To understand my mistake, I outputed the operand polygons to SVG files and I discovered punctures in one of them. I believe Boost.Geometry thinks my polygon is self-intersecting (may be due to precision error with floats ?) - but this polygon itself is the result of a previous union operation.
For info, I attached the SVG file (use inkscape to see it completely since segments are out of the box due to negative coordinates).
I don't know if solutions to this problem exists or if the library is faulty (the bad polygon is the result of an union operation). One workaround would be to detect punctures and remove them, but it's kind of ugly imho...
Some more details: - point coordinates type is float, - I use custom class instead of point_xy model, - polygon winding is counter-clockwise.
Thank you in advance for any help, Olivier
Thanks for the report - can you give more details, especially WKT of the two input polygons? Or the sequence of algorithms you are using? These spikes normally never occur in unions, however in difference they might occur in some circumstances. Is this also happening with double typed data (in case you know)? Regards, Barend
Hi, Thanks for your support ! I exported the two inputs which produce the error during the algorithm execution and I wrote a simple program appart with thoose polygons. I also simplified a little the inputs and i was able to reproduce the problem (see attached source file main.cpp). The toy program has two input polygons and generates the union. Here are the two input polygons: boost::geometry::read_wkt ( "POLYGON((" "-0.973360121250153 0.194701105356216," "-0.923463344573975 0.184775948524475," "-0.858578622341156 0.141421362757683," "0.18477588891983 2.07653665542603," "0.141421347856522 2.1414213180542," "-1.18477594852448 -0.076536700129509," "-1.1414213180542 -0.141421377658844," "-0.973360121250153 0.194701105356216" "))", pa ); boost::geometry::read_wkt ( "POLYGON((" "-0.14142133295536 1.8585786819458," "-1.1414213180542 -0.141421377658844," "-1.07653665542603 -0.184775933623314," "-0.076536625623703 1.81522405147552," "-0.14142133295536 1.8585786819458" "))", pb ); And here is the output polygon, printed to stdout: -0.19351507723331451416 1.5812671184539794922 -0.07653662562370300293 1.8152240514755249023 -0.1414213329553604126 1.8585786819458007812 -0.72200763225555419922 0.69740593433380126953 -1.1847759485244750977 -0.076536700129508972168 -1.1414213180541992188 -0.14142137765884399414 <- A -0.9733600616455078125 0.19470109045505523682 <- here is the puncture -1.1414213180541992188 -0.14142137765884399414 <- point equal to A -1.0765366554260253906 -0.18477593362331390381 -0.89969980716705322266 0.1688976585865020752 -0.85857862234115600586 0.14142136275768280029 0.18477588891983032227 2.0765366554260253906 0.14142134785652160645 2.1414213180541992188 -0.19351507723331451416 1.5812671184539794922 I'll attach the generated SVG for inputs and output. As you suggested, I also tried to use double instead of float. The result is different (note: not all digits printed for doubles) : -0.19351506716472754999 1.5812671771090451855 -0.07653662562370300293 1.8152240514755200174 -0.14142133295535999626 1.8585786819457998931 -0.72200777157880025037 0.69740575279044780821 -1.1847759485244799826 -0.076536700129508999924 -1.1414213180542001069 -0.14142137765884399414 <- A -0.97336012125015303198 0.19470110535621598657 <- one new extra-point -0.97336008742385127235 0.19470109862769818809 <- -1.1414213180542001069 -0.14142137765884399414 <- point equal to A (I checked till last digit, not shown here) -1.0765366554260300536 -0.18477593362331398708 -0.89969984067827302177 0.16889768269682844948 -0.85857862234115600586 0.14142136275768299458 0.1847758889198299892 2.0765366554260298315 0.14142134785652199502 2.1414213180542001069 -0.19351506716472754999 1.5812671771090451855 With double precision, a kind of hole is created instead of a puncture, but I don't know if this should be accepted as a good polygon... One more thing I forgot to mention: I'm using boost 1.53 - I see another version has been released very recently and I think i'll give a try with it asap. I'm not very familiar with Boost.Geometry, so maybe I'm doing something wrong or maybe I'm expecting too much. Regards On Wed, Jul 3, 2013 at 6:04 PM, Barend Gehrels <barend@xs4all.nl> wrote:
Hi,
On 3-7-2013 12:22, Olivier Heriveaux wrote:
Hello !
I'm trying to use Boost.Geometry library to implement Minkowsky algorithm (i.e. polygon convolution). I try to implement it in the same way Boost.Polygon does, but during the algorithm execution, a boost::geometry::overlay_**invalid_input_exception is raised.
It seems that one of the input polygons to the union_ function is invalid. To understand my mistake, I outputed the operand polygons to SVG files and I discovered punctures in one of them. I believe Boost.Geometry thinks my polygon is self-intersecting (may be due to precision error with floats ?) - but this polygon itself is the result of a previous union operation.
For info, I attached the SVG file (use inkscape to see it completely since segments are out of the box due to negative coordinates).
I don't know if solutions to this problem exists or if the library is faulty (the bad polygon is the result of an union operation). One workaround would be to detect punctures and remove them, but it's kind of ugly imho...
Some more details: - point coordinates type is float, - I use custom class instead of point_xy model, - polygon winding is counter-clockwise.
Thank you in advance for any help, Olivier
Thanks for the report - can you give more details, especially WKT of the two input polygons? Or the sequence of algorithms you are using? These spikes normally never occur in unions, however in difference they might occur in some circumstances. Is this also happening with double typed data (in case you know)?
Regards, Barend ______________________________**_________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/**mailman/listinfo.cgi/boost-**users<http://lists.boost.org/mailman/listinfo.cgi/boost-users>
Hi Olivier, The policy of this list is: don't top-post. I reordered your mail to read from top to bottom, my answers in between.
It seems that one of the input polygons to the union_ function is invalid. To understand my mistake, I outputed the operand polygons to SVG files and I discovered punctures in one of them. I believe Boost.Geometry thinks my polygon is self-intersecting (may be due to precision error with floats ?) - but this polygon itself is the result of a previous union operation.
I don't know if solutions to this problem exists or if the library is faulty (the bad polygon is the result of an union operation). One workaround would be to detect punctures and remove them, but it's kind of ugly imho...
Some more details: - point coordinates type is float, - I use custom class instead of point_xy model, - polygon winding is counter-clockwise.
Thank you in advance for any help, Olivier
On 5-7-2013 15:05, Olivier Heriveaux wrote:
I exported the two inputs which produce the error during the algorithm execution and I wrote a simple program appart with thoose polygons. I also simplified a little the inputs and i was able to reproduce the problem (see attached source file main.cpp).
Thanks for your sample program and your tests.
I'll attach the generated SVG for inputs and output. As you suggested, I also tried to use double instead of float. The result is different (note: not all digits printed for doubles) :
-1.1414213180542001069 -0.14142137765884399414 <- A -0.97336012125015303198 0.19470110535621598657 <- one new extra-point -0.97336008742385127235 0.19470109862769818809 <- -1.1414213180542001069 -0.14142137765884399414 <- point equal to A (I checked till last digit, not shown here)
My version with high precision (ttmath): -1.1414213180542 -0.141421377658844 (point of both pa and pb) -0.973360121250153 0.194701105356216 (point of pa) -0.9733600874238512128115932867815276942 0.19470109862769819504261957771496882692 (generated point) -1.1414213180542 -0.141421377658844 (point of both pa and pb)
One more thing I forgot to mention: I'm using boost 1.53 - I see another version has been released very recently and I think i'll give a try with it asap.
This behaviour is not changed.
I'm not very familiar with Boost.Geometry, so maybe I'm doing something wrong or maybe I'm expecting too much.
I tried it with float, double and ttmath and can reproduce your case with all of them. ttmath is expected to be high precision so it is (probably) not really a floating point error. I also tried to make the union with both SQL Server and PostGIS and both give a similar output, including the pseudo-spike. SQL Server makes it one polygon, PostGIS makes it a polygon with a hole. So this case is indeed quite interesting. They both report the output polygon to be valid. A polygon may contain a self-tangency. The whole-like triangle has an area of -0.000000006250291651472502798247346743117038847 so it is in fact not a spike, at least not in ttmath (and according to your report, not in double). So only in float we have the real spike. The output is indeed not checked on these cases. They should not be generated but in float they apparently are, because of the lower resolution. Did you try the complete program (so including the steps after this union) with double? Is it then also reporting the self-intersection? You probably cannot use float for this case... We can filter out the spike in a post-process, as you suggest, but it is (at least not now) the intention to do this by default. Regards, Barend
The policy of this list is: don't top-post. I reordered your mail to read from top to bottom, my answers in between.
Sorry for the inconvenient, I knew it but gmail hid your answer in my reply form (have to click a button to show it)...
So only in float we have the real spike. The output is indeed not checked on these cases. They should not be generated but in float they apparently are, because of the lower resolution.
So this could really be considered as an issue ? Do you think a solution could correct this behaviour or must we deal with it ? I'm not asking for a fix, I currently use Boost.Polygon to achieve what I want - just wanted to test it with Boost.Geometry since it can work with float (I currently convert my float space to int space to work with Boost.Polygon). As I found this corner case I thought it could be usefull to report it.
Did you try the complete program (so including the steps after this union) with double? Is it then also reporting the self-intersection? You probably cannot use float for this case... We can filter out the spike in a post-process, as you suggest, but it is (at least not now) the intention to do this by default.
It requires many changes in my program, it is a currently in a big project (point type is not a template since I knew I wanted floating numbers). I will try to extract the entire algorithm and make a simple test program for it. Regards, Olivier.
Hi Olivier,
So only in float we have the real spike. The output is indeed not checked on these cases. They should not be generated but in float they apparently are, because of the lower resolution.
So this could really be considered as an issue ? Do you think a solution could correct this behaviour or must we deal with it ? I'm not asking for a fix, I currently use Boost.Polygon to achieve what I want - just wanted to test it with Boost.Geometry since it can work with float (I currently convert my float space to int space to work with Boost.Polygon). As I found this corner case I thought it could be usefull to report it.
Sure, your report is very useful. Yes it is an issue, a spike should not be there. I will think about how it can be avoided efficiently. Besides that, another solution (which was already planned for the cases of Volker Schöch) is that the intersection can deal with spikes. The union would then still have a spike, but algorithms later on do not throw on that. I have to do more research on this.
Did you try the complete program (so including the steps after this union) with double? Is it then also reporting the self-intersection? You probably cannot use float for this case... We can filter out the spike in a post-process, as you suggest, but it is (at least not now) the intention to do this by default.
It requires many changes in my program, it is a currently in a big project (point type is not a template since I knew I wanted floating numbers). I will try to extract the entire algorithm and make a simple test program for it.
OK, thanks. Regards, Barend
participants (2)
-
Barend Gehrels -
Olivier Heriveaux