Creating a georeferenced polygon

Hi all,

I'm trying to map out a certain area over southern Africa, which is meant to look like the one in the image. The image was created with the matrix dro_dom_fill containing 1's for the regions of interest and NaN's otherwise. From this matrix, I am trying to create a georeferenced polygon or something similiar, so that I can find gridpoints in another dataset with a different resolution that lie within the domain. However, if I run this code my polygon looks like in droughtdomain_geoshape.jpg attached

[LAT,LON]=meshgrid(lat,lon);
a=dro_dom_fill.*LAT
b=dro_dom_fill.*LON
a(isnan(a))=[]
b(isnan(b))=[]
g=geoshape(a,b,'Geometry','polygon')
worldmap([-35 0],[9 50]), bordersm
geoshow(g)

Answer 1

[KSSV]

Read about inpolygon. As you have the boundary points, you can get all the points lying inside the polygon.

Or, you can arrange your boundary points..in a order using this link and plot the boundary.

[Darragh Kenny]

I have problems creating the polygon itself as a first step...

meaning how do I create a polygon on a map, given the longitudes and latitudes of all the gridpoints that are meant to be in the polygon?

[KSSV]

Have a look on boundary. If you are looking for a boundary of country/ state, you can download shape files.

Answer 2

[Bruno Luong]

You can get a linear connected contour (polygon) by

C = contourc(lat,lon,double(isfinite(dro_dom_fill)),0.5*[1 1]);
C = C(:,2:C(2,1)+1) % Assuming it returns 1 polygon