[geos-devel] Assertion failed during Buffer() on invalid geometry

[John Leslie]

Hello,

So I was just trying to clean up some invalid geometries in a PostGIS 
database, using Buffer(the_geom, 0), when I had GEOS fail an assertion 
on me:

[local]:vmap0=# select IsValid(the_geom) from bad_geom;
NOTICE:  Ring Self-intersection at or near point -67.1954 44.9132
 isvalid
---------
 f
[local]:vmap0=# select Buffer(the_geom, 0) from bad_geom;
server closed the connection unexpectedly

The last line in the postgres serverlog before it went down was:

[local] SELECT: ../../source/headers/geos/noding/SegmentString.h:175: 
void geos::noding::SegmentString::testInvariant() const: Assertion 
`pts->size() > 1' failed.

The gdb backtrace:

#0  0x00002ae52f25107b in raise () from /lib/libc.so.6
#1  0x00002ae52f25284e in abort () from /lib/libc.so.6
#2  0x00002ae52f24aaf4 in __assert_fail () from /lib/libc.so.6
#3  0x00002ae531b18bcb in 
geos::noding::SegmentString::notifyCoordinatesChange (this=0x13b30a0)
    at ../../source/headers/geos/noding/SegmentString.h:175
#4  0x00002ae531b197d6 in geos::noding::ScaledNoder::scale (this=<value 
optimized out>, segStrings=<value optimized out>)
    at ScaledNoder.cpp:160
#5  0x00002ae531b198bf in geos::noding::ScaledNoder::computeNodes 
(this=0x7fff7bd57940, inputSegStr=0x7fff7bd57710)
    at ScaledNoder.cpp:205
#6  0x00002ae531b1f783 in 
geos::operation::buffer::BufferBuilder::computeNodedEdges 
(this=0x7fff7bd578d0,
    bufferSegStrList=@0x7fff7bd57710, precisionModel=<value optimized 
out>) at BufferBuilder.cpp:258
#7  0x00002ae531b1fa3e in geos::operation::buffer::BufferBuilder::buffer 
(this=0x7fff7bd578d0, g=0x976170, distance=0)
    at BufferBuilder.cpp:146
#8  0x00002ae531b21e6a in 
geos::operation::buffer::BufferOp::bufferFixedPrecision 
(this=0x7fff7bd57ab0,
    fixedPM=@0x7fff7bd57a30) at BufferOp.cpp:232
#9  0x00002ae531b21fe4 in 
geos::operation::buffer::BufferOp::bufferReducedPrecision 
(this=0x7fff7bd57ab0,
    precisionDigits=<value optimized out>) at BufferOp.cpp:196
#10 0x00002ae531b2203c in 
geos::operation::buffer::BufferOp::bufferReducedPrecision 
(this=0x7fff7bd57ab0) at BufferOp.cpp:145
#11 0x00002ae531b2243e in 
geos::operation::buffer::BufferOp::getResultGeometry (this=0x7b4a, 
nDistance=44494)
    at BufferOp.cpp:96
#12 0x00002ae531b2259b in geos::operation::buffer::BufferOp::bufferOp 
(g=<value optimized out>, distance=0,
    quadrantSegments=8, nEndCapStyle=0) at BufferOp.cpp:88
#13 0x00002ae531802f8a in GEOSBuffer (g1=0x7b4a, width=44494, 
quadrantsegments=31562) at geos_c.cpp:843
#14 0x00002ae5316bfa77 in buffer (fcinfo=0x7fff7bd57bf0) at 
lwgeom_geos_c.c:776
#15 0x00000000004fdf2d in ExecMakeFunctionResult ()

it looks like pts->size() was 1:

(gdb) print pts->getSize()
$2 = 1

If I run the query with GEOS compiled with NDEBUG, I get:

[local]:vmap0=# select Buffer(the_geom, 0) from bad_geom;
NOTICE:  IllegalArgumentException: Cannot compute the quadrant for two 
identical points -67528 44494
ERROR:  GEOS buffer() threw an error!

This occurs with both svn rev 2029 and 3.0.0r4 (with PostGIS 1.3.1 and 
PG 8.2.5).

A copy of the shapefile of the geometry that broke is at 
http://66.234.145.9/~jleslie/bad_geom.tgz .  FWIW, the invalid geometry 
in question is for the '046HH' boundary in tiger/line's 2004 zcta layer.

BTW, are there any other recommended ways of "fixing" this type of 
invalid geometry besides Buffer()?

Thanks,

John