Postgis 2.1 st_distance between geographies wrong

[mamay]

Results between the below queries are very different (but assumed to be identical, or very closed):

1) SELECT st_distance('SRID=4283;LINESTRING(149.386990599235 -26.3567415843982,149.386990599247 -26.3567415843965,149.387026257283 -26.3567362980298,149.387125078815 -26.3567216575441,149.387223900317 -26.3567070169918,149.387322721788 -26.356692376373,149.387421625802 -26.3566777343106,149.387520447213 -26.3566630935584,149.387619268592 -26.3566484527397,149.387718089941 -26.3566338118544,149.38781691126 -26.3566191709025,149.387915732548 -26.3566045298841,149.388014553806 -26.356589888799,149.388113375033 -26.3565752476473,149.38821219623 -26.356560606429,149.388311017396 -26.3565459651442,149.388409838532 -26.3565313237927,149.38850874221 -26.3565166809971,149.388607563285 -26.3565020395124,149.388706384329 -26.3564873979611,149.388720054423 -26.3564853653255,149.388755888538 -26.3564806169646,149.388805686816 -26.3564760867424,149.388855694739 -26.3564737184747,149.388905749016 -26.3564736051138,149.388955768932 -26.3564758382342,149.388991180786 -26.3564786760044,149.389005666353 -26.3564801486226,149.389105155017 -26.3564899474185,149.389204726265 -26.3564997447661,149.389304295669 -26.3565094518463,149.389403866939 -26.356519249053,149.38950343822 -26.3565290461892,149.389603009512 -26.3565388432549,149.389702580815 -26.3565486402502,149.389802152129 -26.356558437175,149.389901723455 -26.3565682340293,149.390001294791 -26.3565780308132,149.390100864283 -26.3565877373297,149.390200435641 -26.3565975339727,149.390300007011 -26.3566073305452,149.390399578391 -26.3566171270472,149.390499149782 -26.3566269234787,149.390598721185 -26.3566367198398,149.390698210025 -26.3566465175092,149.39079778145 -26.3566563137294,149.390897352885 -26.3566661098792,149.390996922476 -26.3566758157616,149.391096493934 -26.3566856117704,149.391138458852 -26.3566897832034)'::geometry::geography, 'SRID=4283;POINT(149.386990599235 -26.3567415843982)'::geometry::geography);

— results 15630629.1006441 meters!

2) SELECT st_distance(st_transform('SRID=4283;LINESTRING(149.386990599235 -26.3567415843982,149.386990599247 -26.3567415843965,149.387026257283 -26.3567362980298,149.387125078815 -26.3567216575441,149.387223900317 -26.3567070169918,149.387322721788 -26.356692376373,149.387421625802 -26.3566777343106,149.387520447213 -26.3566630935584,149.387619268592 -26.3566484527397,149.387718089941 -26.3566338118544,149.38781691126 -26.3566191709025,149.387915732548 -26.3566045298841,149.388014553806 -26.356589888799,149.388113375033 -26.3565752476473,149.38821219623 -26.356560606429,149.388311017396 -26.3565459651442,149.388409838532 -26.3565313237927,149.38850874221 -26.3565166809971,149.388607563285 -26.3565020395124,149.388706384329 -26.3564873979611,149.388720054423 -26.3564853653255,149.388755888538 -26.3564806169646,149.388805686816 -26.3564760867424,149.388855694739 -26.3564737184747,149.388905749016 -26.3564736051138,149.388955768932 -26.3564758382342,149.388991180786 -26.3564786760044,149.389005666353 -26.3564801486226,149.389105155017 -26.3564899474185,149.389204726265 -26.3564997447661,149.389304295669 -26.3565094518463,149.389403866939 -26.356519249053,149.38950343822 -26.3565290461892,149.389603009512 -26.3565388432549,149.389702580815 -26.3565486402502,149.389802152129 -26.356558437175,149.389901723455 -26.3565682340293,149.390001294791 -26.3565780308132,149.390100864283 -26.3565877373297,149.390200435641 -26.3565975339727,149.390300007011 -26.3566073305452,149.390399578391 -26.3566171270472,149.390499149782 -26.3566269234787,149.390598721185 -26.3566367198398,149.390698210025 -26.3566465175092,149.39079778145 -26.3566563137294,149.390897352885 -26.3566661098792,149.390996922476 -26.3566758157616,149.391096493934 -26.3566856117704,149.391138458852 -26.3566897832034)'::geometry, 999155), st_transform('SRID=4283;POINT(149.386990599235 -26.3567415843982)'::geometry, 999155));

— result 0, which is correct.

POSTGIS="2.1.0beta3dev r11503" GEOS="3.3.8-CAPI-1.7.8" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.10dev, released 2011/12/29" LIBXML="2.7.3" LIBJSON="UNKNOWN" RASTER

OSX 10.7.5

same result on ubuntu 11.10 postgis 2.1

[mamay]

PostgreSQL 9.2.4 on x86_64-apple-darwin11.4.2, compiled by Apple clang version 4.1 (tags/Apple/clang-421.11.66) (based on LLVM 3.1svn), 64-bit

[pramsey]

Replicated here, OSX 10.6. Since the test point is equal to the first point, the answer should certainly be zero, so there's something interesting going on there.

[pramsey]

Also demonstrable with a much smaller line:

SELECT st_distance(
  'SRID=4283;LINESTRING(149.386990599235 -26.3567415843982,149.386990599247 -26.3567415843965)'::geometry::geography, 
  'SRID=4283;POINT(149.386990599235 -26.3567415843982)'::geometry::geography);

[pramsey]

And noting that the line is small in the absolute sense. The start and end points are extremely close together. I've added tests to cunit but they curiously are not duplicating the error, so I'll have to trace it in the backend.

[pramsey]

Found a little corner case in the distance logic, amazing it survived this long.

Fixed in trunk at r11535, 2.0 at r11536, 1.5 at r11537