I want the points that located in a certain polygon

Hey,

I have 92 points. Each point has latitude and longitude. On the other hand, I have a shape file consist of six different polygons. I want to know which point located in which polygon. For example, I want to have all points located in the first polygon.

filename ='Basin1_waterse_ir.shp'
S = shaperead(filename)
S = 
  6×1 struct array with fields:
    Geometry
    BoundingBox
    X
    Y
    DEGREE1
    HECTARES
    AREA
    PERIMETER
    x0xE40xC70xE3
    ACRES

Thank you all.

[darova]

What abuot inpolygon?

[BN]

Dear darova,

I used inpolygon, here is my code, but I don't know what my mistake is; because I can't index any point in polygon 1 for example. Do you know what I do wrong?

clear; clc;
filename ='Basin1_waterse_ir.shp'
S = shaperead(filename);
polygon1_x = S(1).X;     % for example, I want to find all points in polygon number one
polygon1_y = S(1).Y;

polygon1_x = polygon1_x.';
polygon1_y = polygon1_y.';

lat = Points.lat;
lon = Points.lon;

[in,on] = inpolygon(lat,lon, polygon1_x,polygon1_y);        % Logical Matrix

inon = in | on;                                             % Combine ‘in’ And ‘on’
idx = find(inon(:));                                        % Linear Indices Of ‘inon’ Points
latcoord = lat(idx);                                        % X-Coordinates Of ‘inon’ Points
loncoord = lon(idx);                                        % Y-Coordinates Of ‘inon’ Points
figure(1)
plot(lat, lon, 'bp')                                        % Plot All Points
hold on
plot(polygon1_x, polygon1_y, '-r')                          % Plot Polygon
plot(latcoord, loncoord, 'gp')                              % Overplot ‘inon’ Points
hold off

Thank you

[darova]

You have points of 1e+5 scale. What are units of them? How to rescale them to lat/long?

[BN]

Dear darova,

I searched a lot and downloaded a new shapefile with latitude and longitude scales. I uploaded it here in this comment.

After running the modified code below, using this new shapefile I have some points in the polygon but I don't know how to select them because all inon cells are zero.

filename ='subbas_degree1.shp'
S = shaperead(filename);
polygon1_y = S(1).X;     % for example, I want to find all points in polygon number one
polygon1_x = S(1).Y;

polygon1_x = polygon1_x.';
polygon1_y = polygon1_y.';

lat = Points.lat;
lon = Points.lon;

[in,on] = inpolygon(lon,lat,polygon1_x,polygon1_y);        % Logical Matrix

inon = in | on;                                             % Combine ‘in’ And ‘on’
idx = find(inon(:));                                        % Linear Indices Of ‘inon’ Points
latcoord = lat(idx);                                        % X-Coordinates Of ‘inon’ Points
loncoord = lon(idx);                                        % Y-Coordinates Of ‘inon’ Points
figure(1)
plot(lon, lat, '.')                                        % Plot All Points
hold on
plot(polygon1_y, polygon1_x, '.')                          % Plot Polygon
plot(latcoord, loncoord, 'gp')                             % Overplot ‘inon’ Points
hold off

I would like to index inside polygon points in order to choose them from Points.mat

Thank you again

Answer 1

[darova]

You use different order of lan/lot. Change places in red squares

[BN]

Thank you so much