Golang create wkb.Polygon from a list of coordinates

Question

I have lists of coordinates in a file which I want to get their polygon. I used wkb library to load the coordinates, but when I try to set them into the wkb.Polygon object, I get an error:

panic: interface conversion: interface {} is [][][]float64, not [][]geom.Coord

This is my code:

var cc interface {} = collection.Features[0].Geometry.Polygon
c := cc.([][]geom.Coord)
po, err := wkb.Polygon{}.SetCoords(c)

I also tried:

c := collection.Features[0].Geometry.Polygon.([][]geom.Coord)

But I got:

Invalid type assertion: collection.Features[0].Geometry.Polygon.([][]geom.Coord) (non-interface type [][][]float64 on left)

score 4 · Accepted Answer · answered Jan 25 '20 at 19:46

First of all, you need to create a general Polygon like this:

package main

import (
        "fmt"

        "github.com/twpayne/go-geom"
)

func main() {
        unitSquare := geom.NewPolygon(geom.XY).MustSetCoords([][]geom.Coord{
                {{0, 0}, {1, 0}, {1, 1}, {0, 1}, {0, 0}},
        })
        fmt.Printf("unitSquare.Area() == %f", unitSquare.Area())
}

Then you can marshal it into wkb format.

        // marshal into wkb with litten endian
        b, err := wkb.Marshal(unitSquare, wkb.NDR)
        if err != nil {
                fmt.Printf("wkb marshal error: %s\n", err.Error())
                return
        }
        fmt.Println(b)

Golang create wkb.Polygon from a list of coordinates

1 Answers1