--- a/pkg/mesh/vertex.go	Wed Jul 07 12:01:28 2021 +0200
+++ b/pkg/mesh/vertex.go	Wed Jul 07 14:57:30 2021 +0200
@@ -1136,12 +1136,13 @@
 
 // FilterRemoved returns an iterator that only delivers the vertices
 // which indices are not marked as removed.
-func (mpz MultiPointZ) FilterRemoved(removed map[int]struct{}) func() (Vertex, bool) {
-	var idx int
-	return func() (Vertex, bool) {
+func (mpz MultiPointZ) FilterRemoved(removed map[int32]struct{}) func() (Vertex, bool) {
+	var idx int32
+	return func() (v Vertex, ok bool) {
 		for {
-			if idx >= len(mpz) {
-				return Vertex{}, false
+			if idx >= int32(len(mpz)) {
+				ok = false
+				return
 			}
 			if _, rm := removed[idx]; rm {
 				idx++
@@ -1149,7 +1150,9 @@
 			}
 			break
 		}
-		return mpz[idx], true
+		v, ok = mpz[idx], true
+		idx++
+		return
 	}
 }