[postgis-users] Problem with overlay

Tue Jul 3 17:29:46 PDT 2007

Martin, 

Here it is the original LINESTRINGM and the two geometries created from it
with the locate_between_measures function. In theory, their intersection is
a linestring but I might be experiencing the coordinate drift you mentioned.
Now, as I see it, this is a precision problem, not a problem with my
definitions of the geometries. What do you think? 

CREATE TABLE lrs2 (gid int4, road_inv varchar(4)); 
SELECT AddGeometryColumn('lrs2', 'the_geom', 2927, 'LINESTRINGM', 3);
INSERT INTO LRS2 (gid,road_inv, the_geom) VALUES
(1, '290', GeomFromText('LINESTRINGM(2406383.283 861534.851 0.07,2406359.112
861586.107 0.082,2406335.853 861620.089 0.091,2406310.002 861656.69
0.101,2406255.656 861722.092 0.12,2406212.863 861767.807 0.133,2406167.562
861808.508 0.147,2405858.946 862103.134 0.24,2405700.764 862300.136
0.26,2405597.455 862454.556 0.313,2405561.594 862504.091 0.33,2405526.644
862606.293 0.35,2405376.043 863080.764 0.444,2405107.283 863988.701
0.622,2405089.364 864074.548 0.639,2405083.673 864156.245 0.654,2405087.106
864240.691 0.67,2405115.272 864242.612 0.675,2405814.858 864282.694
0.8,2406187.349 864301.081 0.869,2407373.155 864345.473 1.09,2408850.001
864414.309 1.37,2409646.552 864450.813 1.522,2409724.132 864459.6
1.537,2409866.429 864498.596 1.565,2410149.525 864603.864 1.623,2410692.582
864788.24 1.733,2411535.108 865067.94 1.902,2411877.4 865184.391
1.971,2411997.555 865229.746 1.996,2412066.702 865258.947 2.01 ,2412122.725
865291.502 2.022,2412189.604 865347.555 2.039,2413099.432 866096.864
2.264,2413233.115 866208.772 2.297,2413337.133 866308.421 2.325,2413649.134
866597.512 2.406,2414104.962 867058.318 2.53,2414174.266 867117.086
2.547,2414329.433 867259.172 2.586,2414541.968 867377.955 2.631,2415561.425
867898.663 2.843,2415663.666 867950.203 2.865,2415711.381 867964.733
2.874,2415760.712 867974.327 2.883,2415834.682 867983.789 2.897,2415954.61
867986.436 2.919,2417079.882 868026.214 3.128,2417170.24 868029.877
3.145,2417195.169 868042.176 3.15,2417721.664 868392.441 3.27,2417796.276
868423.849 3.285,2418197.637 868559.305 3.366,2418832.192 868788.621
3.495,2419543.831 869053.946 3.641,2419770.891 869135.697 3.687,2419997.995
869225.542 3.733,2421265.462 869754.998 3.996,2421387.091 869796.842
4.021,2421476.281 869826.718 4.038,2421571.488 869846.445 4.057,2421664.639
869860.112 4.075,2421870.976 869869.151 4.115,2422422.273 869893.302
4.22,2423118.185 869912.227 4.351,2423322.658 869910.882 4.39,2423543.675
869887.113 4.432,2423761.002 869840.387 4.474,2423900.347 869825.931
4.5,2425047.751 869848.138 4.717,2425262.25 869851.04 4.757,2425349.276
869854.623 4.773,2425426.24 869868.376 4.788,2425559.956 869900.037
4.814,2425663.321 869931.861 4.834,2425807.25 869981.679 4.863 ,2427651.83
870598.722 5.23,2428262.085 870816.397 5.353,2430198.032 871483.911
5.74,2431505.587 871940.293 6,2432815.135 872390.593 6.26,2435415.059
873293.352 6.78,2437780.605 874089.52 7.257,2437820.359 874103.312 
7.265,2438045.344 874181.343 7.31,2438366.008 874269.892 7.373,2438966.15
874475.042 7.494,2440234.314 874916.234 7.749,2442988.007 875863.599
8.303,2443271.918 875961.321 8.36,2443560.018 876049.762 8.416,2443608.255 
876068.505 8.426,2443666.681 876097.327 8.438,2443732.747 876133.708
8.452,2443788.707 876175.211 8.465,2444125.925 876459.689 8.546,2444432.057
876711.694 8.62,2444631.05 876873.741 8.672,2444787.543 877000.844 
8.712,2444943.989 877119.08 8.751,2445073.637 877200.723 8.782,2445208.325
877277.273 8.813,2445344.218 877342.415 8.843,2445453.449 877396.299
8.868,2445811.841 877539.109 8.945,2445825.476 877557.714 8.95,2445938.059 
877587.195 8.972,2446085.112 877622.033 9,2446299.084 877660.47
9.04,2446608.007 877688.501 9.098,2447923.128 877847.699 9.346,2448425.232
877912.299 9.44,2452388.897 878388.295 10.2,2452678.1 878436.029
10.26 ,2452785.541 878453.306 10.28,2452839.486 878461.985 10.29,2452936.212
878477.791 10.309,2453147.417 878512.326 10.35,2453203.975 878520.16
10.361,2453529.509 878565.275 10.424,2453718.67 878587.397 10.46,2454143.639

878624.842 10.541,2454592.191 878672.24 10.628,2454813.568 878695.375
10.67,2455810.625 878816.796 10.861,2456783.057 878923.353
11.046,2457948.075 879068.144 11.269,2459000.96 879187.493 11.47,2459503.893
879234.27 11.566,2459785.345 879264.009 11.619,2460056.408 879299.012
11.671,2460426.624 879367.34 11.743,2460854.335 879471.822
11.826,2461219.594 879587.06 11.899,2462427.66 879986.859 12.14,2463875.818
880473.917 12.43 ,2464522.953 880697.024 12.558,2465634.74 881112.965
12.78,2466133.525 881277.739 12.86,2466464.64 881418.43 12.931,2468377.709
882145.196 13.333,2469223.238 882450.574 13.51,2470998.744 883136.062
13.871,2471904.723 883482.827 14.055,2472282.975 883623.285
14.132,2474415.388 884367.481 14.56,2476883.851 885294.585
15.057,2477619.048 885577.557 15.205,2478111.881 885802.791
15.307,2478588.523 886044.39 15.408,2479003.256 886276.557 
15.497,2479643.615 886689.823 15.641,2479954.098 886909.531
15.713,2482447.575 888637.839 16.284,2483535.9 889406.806 16.535,2484758.36
890295.507 16.82,2485433.873 890812.227 16.982,2486278.785 891394.59
17.177 ,2486869.777 891816.656 17.315,2487564.761 892296.149
17.475,2488317.986 892821.017 17.649,2489120.621 893384.276
17.836,2489836.725 893868.926 18,2491205.446 894830.469 18.31)', 2927
));

CREATE TABLE road_segments (road_id int4, road_inv varchar(4),begmp real, 
endmp real);
SELECT AddGeometryColumn('road_segments', 'the_geom', 2927, 'LINESTRING',
2);
INSERT INTO road_segments (road_id,road_inv, begmp, endmp) VALUES
(10, '290', 1.48 , 1.79);
UPDATE road_segments SET the_geom =
force_2d(locate_between_measures(lrs2.the_geom,begmp,endmp))
FROM lrs2;

CREATE TABLE curves (curve_id int4, road_inv varchar(4),begmp real, endmp
real);
SELECT AddGeometryColumn('curves', 'the_geom', 2927, 'LINESTRING', 2); 
INSERT INTO curves (curve_id,road_inv, begmp, endmp) VALUES
(100, '290', 1.48, 1.79);
UPDATE curves SET the_geom =
force_2d(locate_between_measures(lrs2.the_geom,begmp,endmp))
FROM lrs2;

SELECT road_id FROM road_segments, curves 
WHERE road_segments.the_geom && curves.the_geom AND
overlaps(road_segments.the_geom, curves.the_geom);

Jonathan Aguero Valverde
Research Assistant and Ph.D. Candidate
Pennsylvania State University
The Pennsylvania Transportation Institute
201 Transportation Research Building
University Park, PA 16802
www.personal.psu.edu/jua130

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Martin
Davis
Sent: Tuesday, July 03, 2007 8:07 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Problem with overlay

Can you post the WKT of two linestrings which you think should overlap?

Overlaps has a very narrow definition. For Linestrings, two linestrings 
overlap if and only if their intersection is itself a linestring (i.e. 
they overlap in a point-set of dimension 1).

I suspect you may be seeing the result of the inevitable coordinate 
drift caused by computing a new coordinate along a line segment. In 
almost all cases, doing this results in two new line segments which are 
NOT coincident with the original.

Jonathan Aguero wrote:
>
> Rhys,
>
> That's the point, they should /overlap/ since they were created from 
> the same linear reference system and the road segment '/contains/' the 
> curve.
>
> I also tried with /intersects/ but the problem is that it picks up 
> more segments than I need. For example if a curve ends at the same 
> point than a road segment; theoretically, the overlaps should pick up 
> only that segment while /intersects/ pick also the following segment 
> that starts when the previous segment ends. Think also in a situation 
> where a road intersection is located in a curve: /intersects /will 
> select the other segments that converge in the intersection even 
> though they have no curves.
>
> Now, I might be misinterpreting what the overlap should do; if this is 
> the case please let me know.
>
> Thanks.
>

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022

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