Opened 6 years ago
Closed 6 years ago
#3329 closed defect (fixed)
Topology population regression
Reported by: | strk | Owned by: | strk |
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Priority: | blocker | Milestone: | PostGIS 2.2.1 |
Component: | topology | Version: | 2.2.x |
Keywords: | Cc: | esseffe, aperi2007 |
Description
Another regression spotted between plpgsql and C version of topology loading. I'm attaching the smallest input found so far, can probably be further reduced. Thanks @esseffe for finding this out.
To reproduce the error:
strk=# select createtopology('rer_exception'); createtopology ---------------- 2650 (1 row) strk=# select topogeo_addpolygon('rer_exception', st_geometryn(geom, 1)) from rer_exception order by gid; ERROR: SQL/MM Spatial exception - geometry crosses edge 58
Switching to the plpgsql version works and returns 60 faces (with a few duplicates and a null, which isn't really expected):
ALTER EXTENSION strk=# select topogeo_addpolygon('rer_exception', st_geometryn(geom, 1)) from rer_exception order by gid; topogeo_addpolygon -------------------- 71 84 71 72 74 76 78 80 82 86 89 91 93 95 96 97 99 87 76 80 88 90 89 92 99 71 73 100 107 106 77 81 110 78 115 71 73 100 107 106 77 81 110 78 115 117 84 82 83 119 86 126 125 130 94 131 93 136 91 96 138 97 142 146 148 149 151 98 95 141 (60 rows)
Attachments (7)
Change History (23)
Changed 6 years ago by
Attachment: | rer_exception.zip added |
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Changed 6 years ago by
Attachment: | rer_err.png added |
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comment:2 Changed 6 years ago by
comment:3 Changed 6 years ago by
The topology summary, to get an idea:
strk=# select topologysummary('rer_exception'); topologysummary -------------------------------------------------------- Topology rer_exception (id 2650, SRID 0, precision 0) + 90 nodes, 174 edges, 85 faces, 0 topogeoms in 0 layers+
comment:4 Changed 6 years ago by
The _ST_Mintolerance function returns around 1.79e-08 for the three inputs. Using a smaller tolerance (1e-08) makes the trunk version succeed (returning 91 rows).
comment:5 Changed 6 years ago by
I think the difference here is only between a slightly different values of tolerance computed by the plpgsql version and the C version.
For example, the tolerance for the first polygon is:
1.78950816000000e-08 in 2.2 1.78950805740752e-08 in 2.1
comment:6 Changed 6 years ago by
I confirm that reducing the auto-computed tolerance in 2.2 fixes the import.
comment:7 Changed 6 years ago by
I noticed my liblwgeom is built with -fexcess-precision=standard, now I wonder if that would change the computation of minimal tolerance...
comment:8 Changed 6 years ago by
Adding code to test the computed tolerance shows that what is computed is anyway bigger than it needs be, for example:
psql:load.sql:4: NOTICE: computed minTolerance: 1.78950811259422e-08 psql:load.sql:4: NOTICE: minTolerance 8.94754056297112e-09 is also good psql:load.sql:4: NOTICE: minTolerance 4.47377028148556e-09 is also good psql:load.sql:4: NOTICE: minTolerance 2.23688514074278e-09 is also good psql:load.sql:4: NOTICE: minTolerance 1.11844257037139e-09 is also good psql:load.sql:4: NOTICE: minTolerance 5.59221285185695e-10 is also good psql:load.sql:4: NOTICE: final minTolerance: 5.59221285185695e-10
comment:9 Changed 6 years ago by
For "it needs be" I mean that comparing the number of interest (max ordinate value) with the same value minus or plus the tolerance finds them different.
comment:10 Changed 6 years ago by
Changing the min tolerance computation to use this method (halving tolerance while still good) changes behaviour with some of the cases in regress/topogeo_addlinestring, but doesn't introduce any load failure there. I think it would make sense to get "min tolerance" correctly, somehow (still a research matter)
comment:11 Changed 6 years ago by
It looks there's a GNU library specifically for getting this right: http://www.mpfr.org/
comment:12 Changed 6 years ago by
Just to get a feel of what does it take: https://gforge.inria.fr/scm/viewvc.php/mpfr/branches/3.1/src/next.c?revision=9403&view=markup&pathrev=9605#l27
And this is half of the story (next-to-zero). There's a next-to-infinite too ...
Changed 6 years ago by
Attachment: | issue_topology_intersection.zip added |
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package reduce to produce the intersection issue
comment:13 Changed 6 years ago by
Hi strk, I add a new packege with a really reduced dataset to produce the intersection issue.
Also an image to explain the question:
The topology has the two edge 58 and 59 loaded. Has you can notice the edge 58 is at right of the 59 edge. Also you can notice the new line to add to the topology (red line) is at left side.
The procedure find before the 58 edge and try to link the new line (red) to the 58 edge and this trigger the intersection with the 59 edge.
ut perhaps thre is more. Infact say-ing that the 58 edge is find before the 59 edge could be not sufficient to explain why it is choose. Infact I remenber that in the core of geos some year ago was done an enhancement to allow the geos snap to find the nearest feature not only the first feature under the snap limit.
(see the geos ticket https://trac.osgeo.org/geos/ticket/501)
If this code is still in geos and active (and is used in this procedure) the explanation is not only that the 58 edge is found before the 59 edge but instead is that the 58 edge has a vertex nearest to the newline (red) rather than the 59 edge.
The image show this kind of use-case, as you can see the vertex (blue) of the 58 edge is near to the red line rather than the two vertex s of the 59 edge.
This could explain why the procedure choose the 58 edge instead of the 59 edge and to so the intersection fail.
regards.
Andrea.
If this enhancemente for snap geos is still in geos core the explanation to why
comment:15 Changed 6 years ago by
Cc: | aperi2007 added |
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comment:16 Changed 6 years ago by
Resolution: | → fixed |
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Status: | new → closed |
initial test, 3 polygons with 12, 88 and 988 vertices each