How To Check If A Coordinate Pair (lat,lon) Exists In A Coordinate Grid?

I have an algorithm that computes shapes using geographic coordinates when certain conditions are satisfied. The algorithm outputs a latitude list and a longitude list like seen be

Solution 1:

Since you have real values you cannot check with ==. So we have to use windows confined by inequalities. As a result we get the indices of the elements within the choosen window (11 and 12 in this example)

# 1. build numpy arrays
lat = np.array([-47.25, -47.25, -47.25, -48.,   -48.,   -48.,   -48.,   -48.,   -48.,   -48., -48.,   -48.75, -48.75, -48.75, -48.75, -48.75, -48.75, -49.5,  -49.5,  -49.5, -49.5,  -50.25, -50.25, -50.25])
lon= np.array([225.75, 226.5,  227.25, 226.5,  227.25, 228.,   228.75, 229.5,  230.25, 231., 231.75, 228.,   228.75, 229.5,  230.25, 231.,   231.75, 229.5,  230.25, 231., 231.75, 230.25, 231., 231.75])


# 2. pick the values in the desired window for each data series, set to zeros the others
La = np.where( (lat> -49.0) & (lat<-48), lat, 0*lat)
Lo = np.where( (lon>226) & (lon<229), lon, 0*lon)

#3. give the indices where both series are non-zero
ind = np.argwhere(np.abs(Lo*La)>0.0001)
ind
array([[11],
       [12]], dtype=int64)

Or If you prefere an array with booleans:

(np.abs(Lo*La)>0.0001).astype(int)
array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
       0, 0])

Solution 2:

Try this:

import numpy as np

lat_alg = np.array([-47.25, -47.25, -47.25, -48., -48., -48., -48., -48., -48.,
                    -48., -48., -48.75, -48.75, -48.75, -48.75, -48.75, -48.75,
                    -49.5, -49.5, -49.5, -49.5, -50.25, -50.25, -50.25])
lon_alg = np.array([225.75, 226.5, 227.25, 226.5, 227.25, 228., 228.75, 229.5,
                    230.25, 231., 231.75, 228., 228.75, 229.5, 230.25, 231.,
                    231.75, 229.5, 230.25, 231., 231.75, 230.25, 231., 231.75])

desired_position = np.array([-47.5, 228])
tolerance = 1

lat = np.abs(lat_alg - desired_position[0]) <= tolerance
lon = np.abs(lon_alg - desired_position[1]) <= tolerance 

desired_area = np.outer(lat, lon).astype(int)

If you want to compare exact matches instead of coordinate windows, try using numpy.isclose to avoid float-point discrepancies:

import numpy as np

lat_alg = np.array([-47.25, -47.25, -47.25, -48., -48., -48., -48., -48., -48.,
                    -48., -48., -48.75, -48.75, -48.75, -48.75, -48.75, -48.75,
                    -49.5, -49.5, -49.5, -49.5, -50.25, -50.25, -50.25])
lon_alg = np.array([225.75, 226.5, 227.25, 226.5, 227.25, 228., 228.75, 229.5,
                    230.25, 231., 231.75, 228., 228.75, 229.5, 230.25, 231.,
                    231.75, 229.5, 230.25, 231., 231.75, 230.25, 231., 231.75])

desired_position = np.array([-47.5, 228])

lat = np.isclose(lat_alg - desired_position[0], 0)
lon = np.isclose(lon_alg - desired_position[1], 0)

exact_matches = np.outer(lat, lon).astype(int)

Both desired_area and exact_matches are 2d arrays with shape (len(lat), len(lon)).

Solution 3:

In order to be totally sure about if the pair exists, I suggest you build a list of tuples where each tuple contains a pair (lat,lon). For example:

def Mesh(X,Y):
    A=[]
    for x,y in zip(X,Y):
        A.append((x,y))

    return A

Coord=Mesh(lat_alg,lon_alg)

Then, if you know your grid resolution, you can easily check a pair as follows:

coord=(-49.5,230.25)

if coord in Coord:
    print('True')
else:
    print('False')