Issue rendering compound polygons (PostGIS)

[tbonfort]

Some arcs end up drawn as full circle. See the center of the attached image, the red circle.

test-data, same eâs shown in image (sql dump) can be found here:
www.tydac.ch/download/compound_test.zip

[flavster58]

maybe it is not clear enough: the circle should NOT be there. seems that some arcs go "banana".

[jratike80]

It has for sure taken too long without any feed back for you but as least for me it was not very easy to install the test data. For some reason the backup file was not recognized by my pgAdmin and I had to run the SQL commands by hand, as well as to save the data section into text file for importing it with COPY. I would have appreciated also a section of mapfile.

LAYER
NAME "compound_pg"
STATUS ON
CONNECTIONTYPE POSTGIS
CONNECTION "dbname=test user=testuser"
DATA "geom from compound_test using unique bfs_nr"
PROCESSING "CLOSE_CONNECTION=DEFER"
TYPE LINE
STATUS ON
PROJECTION
"init=epsg:21781"
END
...

Anyway, I could reproduce the issue with Mapserver 7.0 and I can also see some full circles on the map. Next step would be to get one such geometry into a cage.

[jrahkonen]

I wonder if this QGIS issue has the same roots https://hub.qgis.org/issues/13893.

[ezala]

As suspected by jrahkonen this is also an (closed) issue in QGIS (https://hub.qgis.org/issues/13893) and PostGIS (https://trac.osgeo.org/postgis/ticket/3099).

I was also able to reproduce the problem with a simple feature - kind of oval - formed by 2 circular strings and 2 lines.

When the distance between the points of the circular strings is sufficiently big the feature is drawn correctly by mapserver, but when it comes to cm or mm ranges the curves are completely wrong:

1m radius (correct):

1dm radius (correct):

1mm radius (wrong):

The problem can be solved by patching arcCircleCenter in mappostgis.c with the solution proposed by PostGIS (https://trac.osgeo.org/postgis/ticket/3099).

Example mapfile:
map.txt
Example data:
pg_data.txt
mappostgis.c patch provided by PostGIS:
arc_circle_center_patch.txt

[jmckenna]

Tested successfully using @ezala's ovals, in PostgreSQL 9.5.4 and PostGIS 2.2.2