modifying vertices of geopolyshape

Hi,

I can modify an existing polyshape plot as follows:

Vertices = [0 0 2 2; 2 0 0 2]';
NewVertices = [0 0 2 2; 2 0 0 3]';
pgon = polyshape(Vertices);
p = plot(pgon,'FaceColor','red','FaceAlpha',0.1);
p.Shape.Vertices = NewVertices;

however I can't do the same thing with geopolyshape, since I could not find any properties of it which stores the lat,lon coords. Essentially, I want to enable moving a geopolyshape incrementally with user commands. I would be glad if you anybody could advise.

Thank you,

Murat

Answer 1

[Geetla Sindhu]

Hello Murat,

I understand that you are trying to use geopolyshape with geographic coordinates.

You can try the following workaround to solve the issue:

• A geopolyshape object represents a polygon or multipolygon in geographic coordinates. Use the geopolyshape function.

    shape = geopolyshape(lat,lon)

This function creates a polygon with vertices at the specified latitude and longitude coordinates.

• Then geoplot is used to plot the point, line, or polygon shape objects in shape on a geographic axes.

     pg = geoplot(shape)

Now pg is a polygon object with different properties and they be accessed using dot notation.

For example:

shape = geopolyshape([1 10 1 1],[1 1 10 1] );

pg = geoplot(shape);

pg.FaceColor = "r";

Hope this resolves your issue.

You can also refer to Geographic polygon appearance and behavior - MATLAB (mathworks.com) for further information regarding polygon properties.

Thank you.

[Murat Panayirci]

Hi Geetla,

my problem is that the object pg you created with geoplot does not have a "Vertices" field (as in the regular polyshape plot) which I can modify. see below

shape = geopolyshape([1 10 1 1],[1 1 10 1] );
pg = geoplot(shape);
>> pg.ShapeData
ans = 
geopolyshape with properties:
NumRegions: 1
NumHoles: 0
Geometry: "polygon"
CoordinateSystemType: "geographic"
GeographicCRS: []

>> pgon = polyshape([0 0 2 2],[2 0 0 2]);
>> p = plot(pgon,'FaceColor','red','FaceAlpha',0.1);
>> p.Shape
ans = 
polyshape with properties:
Vertices: [4×2 double]
NumRegions: 1
NumHoles: 0

as you can see pg.ShapeData or any other field that I checked does not enable me to easily update the geoplot by updating the coords of vertices. Whereas for polyshape, I can do that as I have mentioned in my original post.

So my question is: how can I modify the geoplot of a geopolyshape, without replotting it?

thanks,

Murat

Answer 2

[Kelly Kearney]

Old question, but I was working through this same problem when needing to reproject a mappolyshape. It appears that the vertex coordinates are hidden in the undocumented object properties InternalData.VertexCoordinateData1 and InternalData.VertexCoordinateData2. They appear to be modifiable*.

shape = geopolyshape([1 10 1 1],[1 1 10 1]);
geoplot(shape);
hold on
shape.InternalData.VertexCoordinate2 = [1 1 5 1];
geoplot(shape, 'r')

*usual disclaimer that undocumented stuff is liable to change and thus break code. I tested this to R2023a and the Answers site used 2024b to render this.