sorokine · December 30, 2015 06:38 · Dec 4, 2013 · Dec 4, 2013 · Dec 4, 2013 · Dec 4, 2013
diff --git a/gistfile1.md b/gistfile1.md
@@ -1,24 +1,24 @@
 # Random point in polygon in PostGIS
 
-Existing function for generating of randon point in polygon in PostGIS may take a very long time in narow and long polygons because the functions have to test lots of points that fall within bounding rectangle but outside actual polygon.
+Existing function for generating of random point in polygon in PostGIS may take a very long time in narrow and long polygons because the functions have to test lots of points that fall within bounding rectangle but outside actual polygon.  Examples are [here](https://github.com/pedrogit/postgisaddons/) and [here](http://sorokine.blogspot.com/2011/05/postgis-function-for-random-point.html).
 
-The idea is to use a funtion to subdivide bounding rectangle recursively and process only tiles that ovrlap with the polygon:
+The idea is to use a function to subdivide bounding rectangle recursively and process only tiles that overlap with the polygon:
 
   1.  subdivide the bounding rectangle into smaller rectangles (2, 4, or more, whichever is easier) 
   2.  randomly pick a rectangle
-  3.  create an interesection of the rectangle with the original polygon, return to the previous step if intersection is empty
-  4.  check if the ratio between the areas of the rectangle and interesection is big enough 
-    * ratio 1:10 means that search for a ppoint in polygon will take roughly 10 interations
+  3.  create an intersection of the rectangle with the original polygon, return to the previous step if intersection is empty
+  4.  check if the ratio between the areas of the rectangle and intersection is big enough 
+    * ratio 1:10 means that search for a point in polygon will take roughly 10 iterations
   5.  if ratio is small enough return the result of normal random point function
 
 One more idea is to modify the point-in-polygon algorithm:
 
   1.  Drop a random point inside the bounding rectangle
   2.  if it is inside the polygon return the result, if not go to the next step
-  3.  create a straight line between the original point and a random point on the boundary of the binding rectangle (this can be done by either choosing a random direction and then finding intersection with the binfing rectangle or by selecting a point on the boundary rectnagle within a random distance from one of the rectangle corners)
+  3.  create a straight line between the original point and a random point on the boundary of the binding rectangle (this can be done by either choosing a random direction and then finding intersection with the binding rectangle or by selecting a point on the boundary rectangle within a random distance from one of the rectangle corners)
   4.  clip the line with the polygon, repeat the previous step if clipped line is empty
   5.  random select a segment of the clipped line
-  6.  create a point on the segment at a random distance from the segment starting vertex (is there a finction in PostGIS for that?)
+  6.  create a point on the segment at a random distance from the segment starting vertex (is there a function in PostGIS for that?)
 
 Or is it possible to rig polygon centroid function to produce a random point instead of the centroid?
 

diff --git a/gistfile1.md b/gistfile1.md
@@ -20,4 +20,6 @@ One more idea is to modify the point-in-polygon algorithm:
   5.  random select a segment of the clipped line
   6.  create a point on the segment at a random distance from the segment starting vertex (is there a finction in PostGIS for that?)
 
-Or is it possible to rig polygon centroid function to produce a random point instead of the centroid?
+Or is it possible to rig polygon centroid function to produce a random point instead of the centroid?
+
+Plus there should be an option to create many random points inside a polygon in one step.
diff --git a/gistfile1.md b/gistfile1.md
@@ -1,8 +1,8 @@
 # Random point in polygon in PostGIS
 
-Existing function for generating of randon point in polygon in PostGIS may take a very long time in narow and long polygons because they have to test lots of point that fall within bounding rectangle but outside those polygon.
+Existing function for generating of randon point in polygon in PostGIS may take a very long time in narow and long polygons because the functions have to test lots of points that fall within bounding rectangle but outside actual polygon.
 
-The idea is to use a recursive funtion that would 
+The idea is to use a funtion to subdivide bounding rectangle recursively and process only tiles that ovrlap with the polygon:
 
   1.  subdivide the bounding rectangle into smaller rectangles (2, 4, or more, whichever is easier) 
   2.  randomly pick a rectangle
@@ -11,11 +11,13 @@ The idea is to use a recursive funtion that would
     * ratio 1:10 means that search for a ppoint in polygon will take roughly 10 interations
   5.  if ratio is small enough return the result of normal random point function
 
-One more idea:
+One more idea is to modify the point-in-polygon algorithm:
 
   1.  Drop a random point inside the bounding rectangle
   2.  if it is inside the polygon return the result, if not go to the next step
   3.  create a straight line between the original point and a random point on the boundary of the binding rectangle (this can be done by either choosing a random direction and then finding intersection with the binfing rectangle or by selecting a point on the boundary rectnagle within a random distance from one of the rectangle corners)
   4.  clip the line with the polygon, repeat the previous step if clipped line is empty
   5.  random select a segment of the clipped line
   6.  create a point on the segment at a random distance from the segment starting vertex (is there a finction in PostGIS for that?)
+
+Or is it possible to rig polygon centroid function to produce a random point instead of the centroid?
diff --git a/gistfile1.md b/gistfile1.md
@@ -1,6 +1,6 @@
 # Random point in polygon in PostGIS
 
-Existing function for generating of randon point in polygon in PostGIS may take a very long time in narow and long polygons because they jave to test lots of point that fall within bounding rectangle but outside those polygon.
+Existing function for generating of randon point in polygon in PostGIS may take a very long time in narow and long polygons because they have to test lots of point that fall within bounding rectangle but outside those polygon.
 
 The idea is to use a recursive funtion that would 
 

diff --git a/gistfile1.md b/gistfile1.md
@@ -0,0 +1,21 @@
+# Random point in polygon in PostGIS
+
+Existing function for generating of randon point in polygon in PostGIS may take a very long time in narow and long polygons because they jave to test lots of point that fall within bounding rectangle but outside those polygon.
+
+The idea is to use a recursive funtion that would 
+
+  1.  subdivide the bounding rectangle into smaller rectangles (2, 4, or more, whichever is easier) 
+  2.  randomly pick a rectangle
+  3.  create an interesection of the rectangle with the original polygon, return to the previous step if intersection is empty
+  4.  check if the ratio between the areas of the rectangle and interesection is big enough 
+    * ratio 1:10 means that search for a ppoint in polygon will take roughly 10 interations
+  5.  if ratio is small enough return the result of normal random point function
+
+One more idea:
+
+  1.  Drop a random point inside the bounding rectangle
+  2.  if it is inside the polygon return the result, if not go to the next step
+  3.  create a straight line between the original point and a random point on the boundary of the binding rectangle (this can be done by either choosing a random direction and then finding intersection with the binfing rectangle or by selecting a point on the boundary rectnagle within a random distance from one of the rectangle corners)
+  4.  clip the line with the polygon, repeat the previous step if clipped line is empty
+  5.  random select a segment of the clipped line
+  6.  create a point on the segment at a random distance from the segment starting vertex (is there a finction in PostGIS for that?)