Indian Latitude Longitude values

Question

I am in need of around 10000 and odd Indian latitude and longitude values for my openlayers project. I have to load them in a postgis db. so a sql file or atleast text file would be better than a link.

Answer 1

This is a nice problem for OGR's python interface. This is my attempt, using world.shp. Here's my code snippet:

from osgeo import ogr # Import ogr
import random # Random number generators etc.

g = ogr.Open ("world.shp") # Open the shapefile with all the world's countries
# Loop over the different features until we find INDIA.
for feat in g.GetLayer(0):
    if feat.GetFieldAsString("NAME").find ("INDIA") >= 0:
        break # We found India, break out of the loop. 
              # feat now holds the feature of INDIA

geom = feat.GetGeometryRef() # Get the geometry of Indina
( lon_min, lon_max, lat_min, lat_max ) = geom.GetEnvelope() # Now get the envelope

n_points = 0 # A counter
india_lon = [] # A list where we'll store longitudes within India
india_lat = [] # A list where we'll store latitudes within India
while n_points < 1000: # Until we reach our required number of points...
    # Draw random longitudes and latitudes within the envelope
    r_lon = random.random()*(lon_max - lon_min ) + lon_min
    r_lat = random.random()*(lat_max - lat_min ) + lat_min
    # Create a point geometry
    pt = ogr.Geometry( ogr.wkbPoint )
    pt.SetPoint_2D( 0, r_lon, r_lat )
    # Is this geometry within india?
    if pt.Within ( geom ):
        # yes! Store the latitude&longitude and update counter
        india_lon.append ( r_lon )
        india_lat.append ( r_lat )
        n_points = n_points + 1
# Save to a CSV file
fp=open("india.txt", 'w' )
fp.write( "Longitude, Latitude\n" )# Header
for (lon, lat) in zip (india_lon, india_lat):
    fp.write ("%f,%f\n" % ( lon, lat ) )

fp.close()

And here's how the result looks like:

Not the most efficient way of dealing with this, but nice to learn :)

Answer 2

You can generate 10000 random points within a polygon of India. There has been some recent work to do this:

• Random Points in Polygon in JTS (Martin Davis' blog)
• Random Point in Polygon for PostGIS (PostGIS wiki)

---

Update I've added a set-returning function to the PostGIS User's wiki, where I've used this question as an example. See that page for details. Although PostGIS also uses a prepared geometry, it isn't as fast as Shapely. My best speed for 10k points is 3023 ms (compared with 1125 ms for Shapely for same problem).