using Geopandas, How to randomly select in each polygon 5 Points by sampling method

Question

I want to select 5 Points in each polygon based on random sampling method. And required 5 points co-ordinates(Lat,Long) in each polygon for identify which crop is grawn.

Any ideas for do this using geopandas?

Many thanks.

Answer 1

My suggestion involves sampling random x and y coordinates within the shape's bounding box and then checking whether the sampled point is actually within the shape. If the sampled point is within the shape then return it, otherwise repeat until a point within the shape is found. For sampling, we can use the uniform distribution, such that all points in the shape have the same probability of being sampled. Here is the function:

from shapely.geometry import Point
def random_point_in_shp(shp):
    within = False
    while not within:
        x = np.random.uniform(shp.bounds[0], shp.bounds[2])
        y = np.random.uniform(shp.bounds[1], shp.bounds[3])
        within = shp.contains(Point(x, y))
    return Point(x,y)

and here's an example how to apply this function to an example GeoDataFrame called geo_df to get 5 random points for each entry:

for num in range(5):
    geo_df['Point{}'.format(num)] = geo_df['geometry'].apply(random_point_in_shp)

There might be more efficient ways to do this, but depending on your application the algorithm could be sufficiently fast. With my test file, which contains ~2300 entries, generating five random points for each entry took around 15 seconds on my machine.