Determining whether a point on earth (given latitude and longitude) is on land or ocean

I am looking for a quick way to determine whether a point on earth's surface (given latitude and longitude) falls on one of the continents or on an ocean.

Any help is greatly appreciated.

Thanks, Deep

[Walter Roberson]

Where do you place the dividing line for estuaries ? Or for reclaimed land?

Answer 1

[Amy Haskins]

You could also try the inpolygon function.

% Load the coastline
coast = load('coast.mat');
ax = worldmap('world'); 
geoshow(coast)

% Grab a point from the map
[lat,lon] = inputm(1,ax);

% Determine if it's within the coast polygon
isInland = inpolygon(lat,lon,coast.lat,coast.long);

Answer 2

[Brett Shoelson]

I think this will do it. It is a binary classifier: Ocean/Land.

coast = load('coast.mat');
[Z, R] = vec2mtx(coast.lat, coast.long, ...
    1, [-90 90], [-90 270], 'filled');
figure; worldmap(Z, R)
geoshow(Z, R, 'DisplayType', 'texturemap')
colormap([0 1 0;0 0 0;0 1 0;0 0 1])
lat = 38.53;%N
lon = -57.07;%W
plotm(lat,lon,'ro')
val = ltln2val(Z, R, lat, lon);
isOcean = val == 2
%isLand = ~isOcean

Cheers,

Brett

[Dan Chavas]

I've put this code into a MATLAB file: http://www.mathworks.com/matlabcentral/fileexchange/45268-landorocean-m

Answer 3

[John]

Perhaps something like this could help:

MATLAB Earth's Topography Demo

Answer 4

[Chad Greene]

landmask(lat,lon) returns 1 for land, 0 for ocean.

Answer 5

[Joshua Carmichael]

The Matlatb function isinterior.m (new since 2022a) does this.

Answer 6

[Kurt]

There is an even simpler solution, similar to Amy Haskins above, that does not even require the use of geo data.

I'm working with digital data. The satellite scans a patch of the Earth and sends back the lat and lon coordinates of each sample point in a 571 x 318 array.

I wanted to use the isinterior() function to tell if a point is inside or outside the shoreline, but it doesn't work with geopolyshape data. I realized that you don't need to use geo objects for this, just a simple axis object.

gx = axes;
load coastlines;
coast = polyshape(coastlon, coastlat)
plot(gx, coast);

Then as you cycle through each satellite lat/lon array, you call isinterior:

idxLand = isinterior(coast,lon,lat);
landlon = lon(idxLand);
landlat = lat(idxLand);

This will clip all the data outside the continents. It works like a charm, without resorting to geo data.