[postgis-devel] Issue 21 in postgis: locate_along_measure: wrong values, invalid data ?

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Issue 21: locate_along_measure: wrong values, invalid data ?
http://code.google.com/p/postgis/issues/detail?id=21

Comment #13 by mark.cav... at siriusit.co.uk:
Hi Richard,

I'm afraid I don't see that result here at all. Here are my results using  
SVN PostGIS
1.3 branch:


Current behaviour:

postgis13=# select asewkt(st_locate_along_measure(ST_GeomFromEWKT('
SRID=31293;LINESTRINGM(
6193.76 5337404.95 4519,
6220.13 5337367.145 4566,
6240.889 5337337.383 4603
)'), 4566));
                                           asewkt
-------------------------------------------------------------------------------------------
  SRID=31293;MULTIPOINTM(1.99915902736236e+37 -1.05616313798637e+45
5.41519507362328e-315,)
(1 row)

postgis13=# select 'LINEZM_6',
asewkt(locate_between_measures('LINESTRING(0 10 10 40, 10 0 0 0)', 2, 2));
  ?column? |        asewkt
----------+----------------------
  LINEZM_6 | POINT(9.5 0.5 0.5 2)
(1 row)


Behaviour with attached patch:

postgis13=# select asewkt(st_locate_along_measure(ST_GeomFromEWKT('
SRID=31293;LINESTRINGM(
6193.76 5337404.95 4519,
6220.13 5337367.145 4566,
6240.889 5337337.383 4603
)'), 4566));
                    asewkt
---------------------------------------------
  SRID=31293;POINTM(6220.13 5337367.145 4566)
(1 row)

postgis13=# select 'LINEZM_6',
asewkt(locate_between_measures('LINESTRING(0 10 10 40, 10 0 0 0)', 2, 2));
  ?column? |        asewkt
----------+----------------------
  LINEZM_6 | POINT(9.5 0.5 0.5 2)
(1 row)


Furthermore with the same patch I see the same results for your extra  
regression tests:

postgis13=# select 'LINEZM_7', asewkt(locate_between_measures('LINESTRING(0  
0 0 0, 1
1 1 1, 2 2 2 2, 3 4 5 6)', 1, 2));
  ?column? |           asewkt
----------+-----------------------------
  LINEZM_7 | LINESTRING(1 1 1 1,2 2 2 2)
(1 row)

postgis13=# select 'LINEZM_8', asewkt(locate_between_measures('LINESTRING(0  
0 0 0, 1
1 1 1, 2 2 2 2, 3 4 5 6)', 1.1, 2.1));
  ?column? |                          asewkt
----------+----------------------------------------------------------
  LINEZM_8 | LINESTRING(1.1 1.1 1.1 1.1,2 2 2 2,2.025 2.05 2.075 2.1)
(1 row)

postgis13=# select 'LINEZM_9', asewkt(locate_between_measures('LINESTRING(0  
0 0 0, 1
1 1 1, 2 2 2 2, 3 4 5 6)', 2, 2));
  ?column? |     asewkt
----------+----------------
  LINEZM_9 | POINT(2 2 2 2)
(1 row)

postgis13=# select 'LINEPZM_1', asewkt(locate_along_measure('LINESTRING(0 0  
0 0, 1 1
1 1, 2 2 2 2, 3 4 5 6)', 0));
  ?column?  |     asewkt
-----------+----------------
  LINEPZM_1 | POINT(0 0 0 0)
(1 row)

postgis13=# select 'LINEPZM_2', asewkt(locate_along_measure('LINESTRING(0 0  
0 0, 1 1
1 1, 2 2 2 2, 3 4 5 6)', 1));
  ?column?  |     asewkt
-----------+----------------
  LINEPZM_2 | POINT(1 1 1 1)
(1 row)

postgis13=# select 'LINEPZM_3', asewkt(locate_along_measure('LINESTRING(0 0  
0 0, 1 1
1 1, 2 2 2 2, 3 4 5 6)', 1.5));
  ?column?  |         asewkt
-----------+------------------------
  LINEPZM_3 | POINT(1.5 1.5 1.5 1.5)
(1 row)


So I'm really confused as to why your results don't match mine?!


ATB,

Mark.



Attachments:
	lwgeom_functions_lrs.patch  631 bytes



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