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annotate schema/isrs_functions.sql @ 1629:9d51f022b8ee

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Introduce SQL function to clip an area to a stretch
author Tom Gottfried <tom@intevation.de>
date Wed, 19 Dec 2018 17:59:31 +0100
parents
children 6646ba22c94a
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1629
9d51f022b8ee Introduce SQL function to clip an area to a stretch
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1 -- Clip an area to a stretch given by a pair of ISRS location codes.
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2 -- Uses the table waterway.distance_marks_virtual to map ISRS location codes
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3 -- to their geo-location and the table waterway.waterway_axis to retrieve
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4 -- perpendicular direction at these geo-locations.
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5 -- Distance marks are assumed to be near the axis and the area passed as
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6 -- argument is assumed to intersect with the axis
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7 -- (use e.g. waterway area or fairway dimensions).
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8 CREATE OR REPLACE FUNCTION ISRSrange_area(
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9 stretch isrsrange,
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10 area geometry
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11 ) RETURNS geometry
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12 AS $$
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13 WITH
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14 -- Get coordinates of location codes
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15 from_geog AS (
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16 SELECT geom FROM waterway.distance_marks_virtual
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17 WHERE location_code = lower(stretch)),
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18 to_geog AS (
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19 SELECT geom FROM waterway.distance_marks_virtual
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20 WHERE location_code = upper(stretch)),
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21 utm_zone AS (
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22 -- Find best matchting UTM zone
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23 SELECT best_utm(ST_Collect(
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24 from_geog.geom::geometry,
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25 to_geog.geom::geometry)) AS z
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26 FROM from_geog, to_geog),
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27 axis AS (
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28 -- Transform and sew together contiguous axis chunks
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29 SELECT ST_LineMerge(ST_Collect(ST_Transform(
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30 wtwaxs::geometry, z))) AS wtwaxs
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31 FROM waterway.waterway_axis, utm_zone),
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32 -- In order to guarantee the following ST_Covers to work,
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33 -- snap distance mark coordinates to axis
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34 from_point AS (
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35 SELECT ST_ClosestPoint(
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36 wtwaxs,
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37 ST_Transform(from_geog.geom::geometry, z)) AS geom
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38 FROM axis, from_geog, utm_zone),
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39 to_point AS (
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40 SELECT ST_ClosestPoint(
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41 wtwaxs,
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42 ST_Transform(to_geog.geom::geometry, z)) AS geom
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43 FROM axis, to_geog, utm_zone),
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44 axis_segment AS (
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45 -- select the contiguous axis on which distance marks lie
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46 SELECT line
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47 FROM (
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48 SELECT (ST_Dump(wtwaxs)).geom AS line
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49 FROM axis) AS lines,
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50 (SELECT ST_Collect(from_point.geom, to_point.geom) AS pts
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51 FROM from_point, to_point) AS points
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52 WHERE ST_Covers(lines.line, points.pts)),
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53 axis_substring AS (
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54 -- Use linear referencing to clip axis between distance marks
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55 SELECT ST_LineSubstring(
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56 axis_segment.line,
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57 ST_LineLocatePoint(axis_segment.line, from_point.geom),
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58 ST_LineLocatePoint(axis_segment.line, to_point.geom)
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59 ) AS line
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60 FROM axis_segment, from_point, to_point),
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61 range_area AS (
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62 -- Create a buffer around the clipped axis, as large as it could
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63 -- potentially be intersecting with the area polygon that
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64 -- intersects with the clipped axis. Get the intersection of that
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65 -- buffer with the area polygon, which can potentially
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66 -- be a multipolygon.
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67 SELECT (ST_Dump(ST_Intersection(
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68 ST_Buffer(
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69 axis_substring.line,
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70 ST_MaxDistance(
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71 axis_substring.line,
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72 ST_Transform(area, z)),
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73 'endcap=flat'),
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74 ST_Transform(area, z)))).geom
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75 FROM axis_substring, utm_zone)
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76 -- From the polygons returned by the last CTE, select only the one
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77 -- around the clipped axis
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78 SELECT ST_Transform(range_area.geom, ST_SRID(area))
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79 FROM axis_substring, range_area
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80 WHERE ST_Intersects(range_area.geom, axis_substring.line)
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81 $$
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82 LANGUAGE sql;