mvt2wkt

main.go

package main

import (
	"fmt"
	"os"

	"github.com/go-spatial/geom/encoding/mvt"
	"github.com/go-spatial/geom/encoding/wkt"
)

func main() {
	tile, err := mvt.Decode(os.Stdin)
	if err != nil {
		fmt.Fprint(os.Stderr, err)
		os.Exit(1)
	}

	col := mvt.TileGeomCollection(tile)

	err = wkt.Encode(os.Stdout, col)
	if err != nil {
		fmt.Fprint(os.Stderr, err)
		os.Exit(1)
	}

	os.Exit(0)
}

no-panic.patch

diff --git a/encoding/mvt/decode.go b/encoding/mvt/decode.go
index dcbe2bf..41a29f6 100644
--- a/encoding/mvt/decode.go
+++ b/encoding/mvt/decode.go
@@ -240,7 +240,10 @@ func decodePoly(buf []uint32) (geom.Geometry, error) {
 			ln := curs.decodeNPoints(cmd.Count(), buf, true)
 			buf = buf[cmd.Count()*2:]
 
-			if windingorder.OfPoints(ln...).IsClockwise() {
+			if windingorder.OfPoints(ln...).IsClockwise() == isCorrect {
+				ret = append(ret, nil)
+			} else if len(ret) == 0 {
+				isCorrect = false
 				ret = append(ret, nil)
 			}
 
@@ -268,6 +271,8 @@ func decodePoly(buf []uint32) (geom.Geometry, error) {
 	}
 }
 
+var isCorrect = true
+
 type decodeCursor struct {
 	x, y float64
 }

Usage:

cat tile.pbf | go run main.go > tile.wkt

Apply the patch to https://github.com/go-spatial/geom/tree/mvt-decode if your mvt might have a bad winding order otherwise the current branch will panic