ST_ISOVist

Signature

GEOMETRY ST_ISOVIST(GEOMETRY point, GEOMETRY obstacles, 
	DOUBLE maxDistance)
GEOMETRY ST_ISOVIST(GEOMETRY point, GEOMETRY obstacles, 
	DOUBLE maxDistance, DOUBLE angleStart, DOUBLE angleStop)

Description

This function compute the visibility polygon obstructed by provided obstacles.

Obstacles can be LINESTRING(S) ,POLYGON(S) or GEOMETRYCOLLECTION(S).

Resulting polygon will be enclosed by a circle defined by the maximum distance (maxDistance) parameter.

Parameters

point : Point coordinates (x, y, (z)) from which the visibility will be calculated,
obstacles : Geometry or set of geometries grouped into a simple or complex geometry, used as obstacles,
maxDistance : Only obstacles located within this distance from the point are considered in the calculation (only cartesian distance is accepted - depends on your spatial ref),
angleStart : Starting angle from which visibility will be calculated (exprimed in radian - to convert from degree, use the H2 database PI() function),
angleStop : Ending angle from which visibility will be calculated (exprimed in radian).

Examples

Initialize input geometries

point where the visibility will be computed : point layer
buildings : polygon layer
walls : linestring layer
buildings and walls : geomCollection layer

DROP TABLE IF EXISTS point, polygon, linestring, geomcollection;

CREATE TABLE point AS SELECT ST_GEOMFROMTEXT('POINT (28.20 59.11)') as the_geom;

CREATE TABLE polygon AS SELECT ST_GEOMFROMTEXT('
	MULTIPOLYGON (((87.1 39 0, 90.8 28.8 0, 80.8 25.3 0, 75.4 40.7 0, 83.1 43.5 0, 87.1 39 0)), ((70.3 67.2 0, 76.3 51.9 0, 79.2 53.1 0, 81.9 46.1 0, 75.3 43.6 0, 72.6 50.5 0, 68 48.6 0, 61.9 63.9 0, 70.3 67.2 0)), ((68 33.6 0, 64.8 32.5 0, 62.3 39 0, 69.1 41.4 0, 70.7 34.8 0, 68 33.6 0)), ((65.4 31.2 0, 69 21.9 0, 55.1 16.3 0, 51.5 25.7 0, 65.4 31.2 0)), ((59.6 85.6 0, 63.4 75.6 0, 54.8 72.5 0, 51.1 82.2 0, 59.6 85.6 0)), 
  ((62 38.3 0, 62.9 36.1 0, 58.8 34.5 0, 57.9 36.7 0, 62 38.3 0)), ((40.4 95.4 0, 39.7 95.3 0, 38.1 99.4 0, 49.1 103.4 0, 55.8 87.4 0, 32.5 78 0, 30.4 82.9 0, 43.3 88 0, 40.4 95.4 0)), ((43.5 64.9 0, 52.2 46.1 0, 50.4 45.3 0, 51.2 43.1 0, 48.7 42.2 0, 46.4 48.5 0, 45.7 48.2 0, 38.7 63.1 0, 43.5 64.9 0)), ((47.2 33.7 0, 49 29.1 0, 46.3 28 0, 44.4 32.8 0, 47.2 33.7 0)), ((25 19.9 0, 28.3 21 0, 28.8 19.1 0, 32.2 20.2 0, 32.8 18.6 0, 43.3 22.1 0, 46.2 13.3 0, 42.6 11.9 0, 42.1 12.9 0, 38.5 11.7 0, 38.6 11 0, 35.5 9.9 0, 35.9 8.8 0, 29.4 7.3 0, 25 19.9 0)), ((43 52.2 0, 44.6 48.4 0, 41.2 47.2 0, 38 47 0, 36.9 49.7 0, 43 52.2 0)), 
  ((24.7 25.6 0, 20.7 37.5 0, 28.3 40.3 0, 31.3 31.5 0, 33.2 32.3 0, 34.4 29.2 0, 24.7 25.6 0)), ((18.2 83.9 0, 16.4 88.4 0, 26.3 92.5 0, 30.1 83.5 0, 16.5 78.2 0, 14.7 82.5 0, 18.2 83.9 0)), ((11.3 21 0, 10 24.9 0, 15.7 27.1 0, 17.2 23 0, 22.6 24.9 0, 23.7 22 0, 20 20.8 0, 19.6 22 0, 17.6 21.4 0, 17 22.9 0, 11.3 21 0)), ((19.3 19.9 0, 21.5 10.5 0, 8.2 7.3 0, 7.2 11.8 0, 9.3 12.3 0, 7.8 19.4 0, 16.1 21.1 0, 18.1 21.2 0, 18.5 19.7 0, 19.3 19.9 0)), ((8.3 64 0, 4.6 74.2 0, 13.8 77.7 0, 17.7 67.4 0, 14.8 66.4 0, 18.7 56 0, 12.2 53.4 0, 8.3 64 0)), ((14 50.8 0, 14.9 48.4 0, 9.6 46.6 0, 12.1 39.1 0, 6 36.9 0, 2.7 46.9 0, 14 50.8 0)))') as the_geom;

CREATE TABLE linestring AS SELECT ST_GEOMFROMTEXT('
	MULTILINESTRING ((54.8 72.5 0, 51.1 82.2 0), (51.1 82.2 0, 59.6 85.6 0), 
	(55.8 87.4 0, 32.5 78 0), (32.5 78 0, 30.4 82.9 0), (45.7 48.2 0, 38.7 63.1 0), 
	(38.7 63.1 0, 43.5 64.9 0), (20.7 37.5 0, 28.3 40.3 0), (30.1 83.5 0, 16.5 78.2 0), 
	(13.8 77.7 0, 17.7 67.4 0), (14.9 48.4 0, 9.6 46.6 0), (9.6 46.6 0, 12.1 39.1 0))') as the_geom;

CREATE TABLE geomcollection AS SELECT ST_GEOMFROMTEXT('GEOMETRYCOLLECTION(
	MULTIPOLYGON (((87.1 39 0, 90.8 28.8 0, 80.8 25.3 0, 75.4 40.7 0, 83.1 43.5 0, 87.1 39 0)), 
	((70.3 67.2 0, 76.3 51.9 0, 79.2 53.1 0, 81.9 46.1 0, 75.3 43.6 0, 72.6 50.5 0, 68 48.6 0, 61.9 63.9 0, 70.3 67.2 0)), 
	((68 33.6 0, 64.8 32.5 0, 62.3 39 0, 69.1 41.4 0, 70.7 34.8 0, 68 33.6 0)), 
	((65.4 31.2 0, 69 21.9 0, 55.1 16.3 0, 51.5 25.7 0, 65.4 31.2 0)), 
	((59.6 85.6 0, 63.4 75.6 0, 54.8 72.5 0, 51.1 82.2 0, 59.6 85.6 0)), 
	((62 38.3 0, 62.9 36.1 0, 58.8 34.5 0, 57.9 36.7 0, 62 38.3 0))), 
	MULTILINESTRING ((55.8 87.4 0, 32.5 78 0), (32.5 78 0, 30.4 82.9 0), (45.7 48.2 0, 38.7 63.1 0), 
	(13.8 77.7 0, 17.7 67.4 0), (14.9 48.4 0, 9.6 46.6 0), (9.6 46.6 0, 12.1 39.1 0)))') as the_geom;

Example with a distance

Using `polygon`

Use buildings (polygon) to compute the visibility from the point with a distance of 20m.

DROP TABLE IF EXISTS isovist;
CREATE TABLE isovist AS 
  SELECT ST_ISOVIST(a.the_geom, b.the_geom, 20) as the_geom 
  FROM point a, polygon b;

Result

Legend : polygon in grey / point in red / resulting ISOVist layer in orange

Same but with a distance of 50m.

DROP TABLE IF EXISTS isovist;
CREATE TABLE isovist AS 
  SELECT ST_ISOVIST(a.the_geom, b.the_geom, 50) as the_geom 
  FROM point a, polygon b;

Result

Legend : polygon in grey / point in red / resulting ISOVist layer in orange

Using `linestring`

Use walls (linestring) to compute the visibility from the point with a distance of 50m.

DROP TABLE IF EXISTS isovist;
CREATE TABLE isovist AS 
  SELECT ST_ISOVIST(a.the_geom, b.the_geom, 50) as the_geom 
  FROM point a, linestring b;

Result

Legend : walls in black / point in red / resulting ISOVist layer in orange

Using `geomCollection`

DROP TABLE IF EXISTS isovist;
CREATE TABLE isovist AS 
  SELECT ST_ISOVIST(a.the_geom, b.the_geom, 50) as the_geom 
  FROM point a, geomcollection b;

Result

Legend : polygon in grey / walls in black / point in red / resulting ISOVist layer in orange

Example with starting and ending angles

Compute the visibility using buildings (poygon layer) with a distance of 50m, starting at 0 rad and ending at 3 rad.

DROP TABLE IF EXISTS isovist;
CREATE TABLE isovist AS 
  SELECT ST_ISOVIST(a.the_geom, b.the_geom, 50, 0, 3) as the_geom 
  FROM point a, polygon b;

Same, but ending at 5 rad.

DROP TABLE IF EXISTS isovist;
CREATE TABLE isovist AS 
  SELECT ST_ISOVIST(a.the_geom, b.the_geom, 50, 0, 5) as the_geom 
  FROM point a, polygon b;

Application : Compute visibility along a path

Aim

Compute visibilities in the city center of Vannes (France), every 10m, with a 100m maximum distance of visibility and export results into an animated .gif file.

Cool isn’t it? Thanks to H2GIS, OrbisGIS, Groovy and The Gimp (all free and open-source) you will see that it’s quite easy to reproduce.

How to produce this animation?

To do so, just follow these steps:

1- Prepare input data
2- Run the Groovy script
3- Convert all the images into an animated .gif

1- Prepare input data

In this example, only two tables are needed:

buildings : a set of polygons (grey in the gif)
path : a linestring. If you want to do a loop (like in the .gif), your linestring has to be closed (red in the gif).

Load your data into OrbisGIS

In the SQL Console, execute the following script.

DROP TABLE IF EXISTS src, iso;

CREATE TABLE src AS 
  SELECT ST_STARTPOINT(the_geom) as the_geom 
  FROM path;     

CREATE TABLE iso AS 
  SELECT ST_IsoVist(a.the_geom, ST_Accum(b.the_geom), 100) as the_geom 
  FROM src a, buildings b;

Where ST_IsoVist(a.the_geom, ST_Accum(b.the_geom), 100) → 100 is the maxDistance value used in this example.

This script will creates:

the first (starting) point of your path (src layer),
the ISOVist (iso layer) from the first point.

Once executed, load src and iso layers into the TOC and adapt their styles to fit to your needs (here red point and orange polygon).

2- Run the Groovy script

In the OrbisGIS’s Groovy Console, execute the script presented below.

In a nutshell, this script will:

densify the path in order to obtain a set of points that will be used to compute visibilities,
for each point, compute the visibility and export the map into a .png file.

import org.orbisgis.core_export.MapImageWriter;
import java.awt.Color;

MapImageWriter mapImageWriter = new MapImageWriter(mc.getLayerModel());
mapImageWriter.setPixelSize(MapImageWriter.MILLIMETERS_BY_INCH / 72);
mapImageWriter.setFormat(MapImageWriter.Format.PNG);
mapImageWriter.setBoundingBox(mc.getBoundingBox());
mapImageWriter.setWidth(729);
mapImageWriter.setHeight(513);
mapImageWriter.setBackgroundColor(Color.WHITE);

for(int i=1;i<=256;i+=1) {
 sql.execute '''
  DROP TABLE IF EXISTS src;
  CREATE TABLE src AS SELECT ST_PointN(ST_Densify(the_geom, 10), '''+i+''') the_geom FROM path;     
  DROP TABLE IF EXISTS iso;
  CREATE TABLE iso AS SELECT ST_IsoVist((SELECT ST_PointN(ST_Densify(the_geom, 10), '''+i+''') the_geom FROM path), ST_Accum(the_geom), 100) the_geom FROM buildings;'''

 FileOutputStream fileOutputStream = new FileOutputStream("/myUrl/"+"test"+i+".png");
 mapImageWriter.write(fileOutputStream, null);
 fileOutputStream.close();
}

Where

mapImageWriter.setWidth(729) and setHeight(513) defines the size (in pixels) of the output .png files,
for(int i=1;i<=256;i+=1) → 256 correspond to the maximum number of image produced (so here the maximum number of point used to compute the visibility along the path),
ST_Densify(the_geom, 10) → 10 is the distance (exprimed in meter) used to densify the path → every 10m a point will be added,
path is the layer name of the linestring used to computes visibilities,
ST_Accum(the_geom), 100) → 100 is the maximum distance used to compute the visibilty (see maxDistance parameter),
buildings is the layer name in which obstacles are stored,
/myUrl/+"test"+i+".png" → .png files, prefixed by test; will be saved into a folder defined by /myUrl/.
src and iso are respectively the output table names for the point where the visibility is calculated and the resulting visibility polygon.

3- Convert all the images into an animated gif

Once the script ran, you obtain many .png files (in this example we have 200 files).

To convert them into an animated .gif file, follow these steps:

Launch The Gimp,
In the File menu, “Open” the first image (here test1.png),
In the File menu, choose “Open as layers” and load the rest of images (here from test2.png to test200.png),

Optionnaly, optimized the rendering for animation → Filters → Animation → Optimize (for GIF),
Export the result : File → Èxport as → choose the .gif file format and specify the file name and output folder → Export,
In the configuration panel, choose Save as animation and you can specify the time between images (by default 100ms) → Export

Your animated .gif file is produced !

ST_ISOVist

Signature

Description

Parameters

Examples

Initialize input geometries

Example with a distance

Using polygon

Using linestring

Using geomCollection

Example with starting and ending angles

Application : Compute visibility along a path

Aim

How to produce this animation?

1- Prepare input data

2- Run the Groovy script

3- Convert all the images into an animated gif

See also

Using `polygon`

Using `linestring`

Using `geomCollection`