Extract coordinates from a geopolyshape

Given a geographic shape object of type geopolyshape:

us_states = readgeotable("usastatehi.shp")

montana = us_states.Shape(us_states.Name == "Montana")

class(montana)

ans =

'geopolyshape'

How could I extract a list of Lat/Lon coordinates of the given shape object (mo_lat, mo_lon)?

% montana

mo_lat = ??? % list of latitudes of Montana polygon edges

mo_lon = ??? % list of longitudes of Montana polygon edges

I know it's possible when loading data using shaperead function instead:

us_states = shaperead("usastatehi.shp")

montana = us_states(26); % 26 is Montana

mo_lat = montana.Y; % list of latitudes of Montana edges

mo_lon = montana.X; % list of longitudes of Montana edges

But I'm curious if it's possible to extract data from existing geopolyshape?

Answer 1

[Jacob Halbrooks]

You can access latitude-longitude coordinates from a geopolyshape using the geotable2table function. We recognize that there is a need to make coordinate data access easier, but in the meantime you can use this approach as a workaround. For example, assuming your table contains geopolyshape data:

GT = readgeotable("myfile.shp");
T = geotable2table(GT,["Lat","Lon"]); 

You can also extract the data into NaN-delimited arrays using polyjoin:

[lat,lon] = polyjoin(T.Lat,T.Lon);

[Sergey Kostrukov]

Thanks, loooks like this is a workaround. The optimal solution for now is to use shaperead I think.

Answer 2

[KSSV]

The present version is much easier. Note that the class of us_states is a table. You can extract the column using:

us_states = readgeotable("usastatehi.shp") ;
class(us_states)

ans = 'table'

us_states.(1)  % first column

ans = 
  16×1 geopolyshape array with properties:

              NumRegions: [16×1 double]
                NumHoles: [16×1 double]
                Geometry: "polygon"
    CoordinateSystemType: "geographic"
           GeographicCRS: [1×1 geocrs]

us_states.LabelLat % third column

ans = 51×1

32.2827 64.6097 34.3451 34.8350 36.8223 39.0295 41.5106 39.1071 28.3914 32.5803

us_states.(4)   % 4th column 

ans = 51×1

-86.9206 -152.4593 -112.0705 -91.8861 -119.6633 -105.5440 -72.7627 -75.4942 -82.8483 -83.0864

[Sergey Kostrukov]

My goal is to extract edge coordiantes of a geopolyshape object, I cannot find any function to do it.

[KSSV]

us_states = readgeotable("usastatehi.shp") ;
plot(us_states.LabelLat,us_states.LabelLon,'.r')

What you want to extract from here?

[Sergey Kostrukov]

LabelLat and LabelLon are suggested coordinates of state name labels, only one lat/lon coordinate per state since only one label.

I'm trying to get access to the list of lat/lon coordinates of the polygon edges forming the shape object.

[Sergey Kostrukov]

Clarified my original question a bit.

[Chad Greene]

I have the exact same question.

The geopolyshape documentation shows how to convert lat,lon coordinates into a geopolyshape:

shape = geopolyshape(lat,lon)

but then offers no guidance on how to get the lat,lon coordinates back out of shape.

I know the coordinates are in there somewhere, I just don't know how to get them back out!

[Sergey Kostrukov]

They are definitely there since geoplot can plot them, but they seems internal only and not exposed to user code.

This has to be a feature request.

[Chad Greene]

This is so frustrating. I don't understand why these new functions have been designed to prevent users from accessing the data we're trying to analyze.

Answer 3

[Chad Greene]

@Sergey Kostrukov I think I found a working solution. The m_shaperead function in M_Map can handle PolygonZ and PolyLineZ data.

[Sergey Kostrukov]

I didn't know about existence of M_Map and it looks amazing! Thank you very much.