Thank you for your help @jerryfaust . How to build a multi-part shape? Do you mean to add all points into one shape? Different shapes may intersect. I want to get the outline of all shapes
Ok. What I think you want is a Union operation. Unfortunately, at this point, the only option through MapWinGIS is the union of 2 shapefiles (Shapefile.Union). This is not too difficult. You can add one shape to one in-memory shapefile, and the other shape to a second shapefile. Then call the Union function. Presuming that the shapes overlap, then the returned shapefile should contain a single shape, being the union of the two shapes.
I’m sorry @zcwbnu , it’s late here, and I’ll have to get back to this tomorrow.
The points in the geometries were being added counter-clockwise, so the polygons were invalid. Just reverse the entry of the points, and as before, make sure to close the polygons. You can verify by calling IsValid and IsValidReason.
Even so, although I can see the two geometries, and their overlap, I am getting a null shapefile returned (effectively because it says the Union is returning no shapes). I don’t yet know why, and I’ll look more tomorrow.