PostGIS – Indian Latitude Longitude Values

datapostgis

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.

Best Answer

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: One thousand random points over India

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

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