| | 1 | = Examples Inside Polygon 2 = |
| | 2 | |
| | 3 | |
| | 4 | '''Temiz [http://postgis.refractions.net/pipermail/postgis-users/2007-October/017242.html asks]:''' |
| | 5 | |
| | 6 | How can I find the points that are in a polygon that have certain distance ( say 4.5m) to polygon's exterior ring ? |
| | 7 | [[BR]] |
| | 8 | |
| | 9 | |
| | 10 | '''Kevin [http://postgis.refractions.net/pipermail/postgis-users/2007-October/017248.html answers]:''' |
| | 11 | |
| | 12 | 1. Extract the exterior ring of your token polygon |
| | 13 | 1. Extract all the interior rings of your polygon |
| | 14 | 1. Find all interior rings that are within a certain distance from the exterior ring |
| | 15 | 1. Buffered the exterior ring |
| | 16 | 1. Compute the intersection of the buffered exterior ring and the interior ring that is "close" |
| | 17 | |
| | 18 | |
| | 19 | {{{ |
| | 20 | -- Create a sample polygon with two interior rings. |
| | 21 | CREATE TABLE sample_poly AS |
| | 22 | SELECT 'POLYGON (( |
| | 23 | 990030.8379 1002264.8323, |
| | 24 | 990029.6966 1002282.0018, |
| | 25 | 990036.8891 1002286.596, |
| | 26 | 990043.8774 1002287.3757, |
| | 27 | 990055.7296 1002285.7607, |
| | 28 | 990067.8854 1002291.298, |
| | 29 | 990073.974 1002293.0334, |
| | 30 | 990078.2256 1002297.9519, |
| | 31 | 990084.8219 1002310.654, |
| | 32 | 990092.914 1002314.2926, |
| | 33 | 990112.8638 1002313.4552, |
| | 34 | 990117.7626 1002311.2194, |
| | 35 | 990121.5065 1002305.1711, |
| | 36 | 990121.2326 1002301.0389, |
| | 37 | 990121.9657 1002294.9971, |
| | 38 | 990118.7723 1002289.1226, |
| | 39 | 990111.6309 1002285.4819, |
| | 40 | 990093.4161 1002281.2291, |
| | 41 | 990074.46 1002277.9317, |
| | 42 | 990067.3481 1002277.3112, |
| | 43 | 990063.0965 1002272.3927, |
| | 44 | 990063.9371 1002265.397, |
| | 45 | 990058.5601 1002259.6862, |
| | 46 | 990034.5683 1002256.5587, |
| | 47 | 990030.8379 1002264.8323 |
| | 48 | ), ( |
| | 49 | 990087.7546 1002286.4867, |
| | 50 | 990110.8467 1002290.5701, |
| | 51 | 990115.2003 1002297.3959, |
| | 52 | 990111.4054 1002302.4905, |
| | 53 | 990094.3804 1002302.209, |
| | 54 | 990081.0698 1002292.8592, |
| | 55 | 990081.768 1002286.6585, |
| | 56 | 990087.7546 1002286.4867 |
| | 57 | ), ( |
| | 58 | 990045.9613 1002265.1177, |
| | 59 | 990051.0778 1002268.9216, |
| | 60 | 990051.2954 1002274.9614, |
| | 61 | 990045.6124 1002282.2855, |
| | 62 | 990039.5748 1002281.5037, |
| | 63 | 990034.4074 1002276.7462, |
| | 64 | 990034.1898 1002270.7064, |
| | 65 | 990038.9005 1002265.4508, |
| | 66 | 990045.9613 1002265.1177 |
| | 67 | ))'::geometry AS geom; |
| | 68 | |
| | 69 | }}} |
| | 70 | |
| | 71 | [[Image(http://postgis.refractions.net/support/wiki/close_points1.png)]] |
| | 72 | |
| | 73 | |
| | 74 | {{{ |
| | 75 | -- Extract exterior ring |
| | 76 | CREATE TABLE exterior_ring AS |
| | 77 | SELECT ST_ExteriorRing(geom) AS geom |
| | 78 | FROM sample_poly; |
| | 79 | |
| | 80 | -- Extract interior rings |
| | 81 | CREATE TABLE interior_rings AS |
| | 82 | SELECT ST_InteriorRingN( |
| | 83 | geom, |
| | 84 | generate_series(1, ST_NumInteriorRings(geom))) AS geom |
| | 85 | FROM sample_poly; |
| | 86 | |
| | 87 | }}} |
| | 88 | |
| | 89 | [[Image(http://postgis.refractions.net/support/wiki/close_points2.png rings)]] |
| | 90 | |
| | 91 | |
| | 92 | {{{ |
| | 93 | -- Identify intersection points of buffered ext ring and interior rings. |
| | 94 | SELECT ST_Intersection(e.buff_geom, i.geom) |
| | 95 | FROM |
| | 96 | (SELECT geom, |
| | 97 | ST_Buffer(geom, 4.5) AS buff_geom |
| | 98 | FROM exterior_ring |
| | 99 | ) AS e, |
| | 100 | interior_rings i |
| | 101 | WHERE ST_DWithin(e.geom, i.geom, 4.5); |
| | 102 | |
| | 103 | }}} |
| | 104 | |
| | 105 | [[Image(http://postgis.refractions.net/support/wiki/close_points3.png close points)]] |
