diff --git a/internal/geom/geom.go b/internal/geom/geom.go
index 034bb23..db77cf3 100644
--- a/internal/geom/geom.go
+++ b/internal/geom/geom.go
@@ -1,3 +1,20 @@
 package geom
 
-//init
+import "math"
+
+const EPS = 1e-6
+
+type Vec struct {
+	X, Y float64
+}
+
+type Seg struct {
+	A, B Vec
+}
+
+func V(x, y float64) Vec        { return Vec{x, y} }
+func Sub(a, b Vec) Vec          { return Vec{a.X - b.X, a.Y - b.Y} }
+func Dot(a, b Vec) float64      { return a.X*b.X + a.Y*b.Y }
+func Cross(a, b Vec) float64    { return a.X*b.Y - a.Y*b.X }
+func Len(a Vec) float64         { return math.Hypot(a.X, a.Y) }
+func NearlyZero(x float64) bool { return math.Abs(x) < EPS }
diff --git a/main.go b/main.go
index 370e405..b7e7d6d 100644
--- a/main.go
+++ b/main.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bspviz/internal/geom"
 	"bspviz/internal/mapfmt"
 	"bspviz/internal/wad"
 	"flag"
@@ -19,6 +20,7 @@ func main() {
 	info := flag.Bool("info", false, "Roh-Infos zur Map (Counts von VERTEXES/LINEDEFS)")
 	extract := flag.String("extract", "", "Kommagetrennte Lump-Namen aus der Map extrahieren (z.B. VERTEXES,LINEDEFS)")
 	outdir := flag.String("out", ".", "Zielordner für -extract")
+	geomtest := flag.Bool("geomtest", false, "Geometrie-Check: Segmente/AABB/Probe-Split ausgeben")
 	flag.Parse()
 
 	if *wadPath == "" {
@@ -100,4 +102,58 @@ func main() {
 			fmt.Printf("wrote %s (%d bytes)\n", dst, len(data))
 		}
 	}
+
+	// Zum debug test der geo functions
+	if *geomtest {
+		raw, err := w.LoadMapLumps(*mapMarker, "VERTEXES", "LINEDEFS")
+		if err != nil {
+			log.Fatalf("load map lumps: %v", err)
+		}
+		m, err := mapfmt.LoadMap(raw)
+		if err != nil {
+			log.Fatalf("parse map: %v", err)
+		}
+
+		segs := mapfmt.LinedefsToSegs(m.Vertices, m.Linedefs)
+		fmt.Printf("GEOM: vertices=%d linedefs=%d segs=%d\n", len(m.Vertices), len(m.Linedefs), len(segs))
+		if len(segs) == 0 {
+			fmt.Println("GEOM: keine Segmente gefunden – prüfe LINEDEFS/VERTEXES")
+			return
+		}
+
+		pts := make([]geom.Vec, 0, len(m.Vertices))
+		for _, v := range m.Vertices {
+			pts = append(pts, geom.V(float64(v.X), float64(v.Y)))
+		}
+		bb := geom.Bounds(pts)
+		w := bb.Max.X - bb.Min.X
+		h := bb.Max.Y - bb.Min.Y
+		fmt.Printf("AABB: min=(%.1f,%.1f) max=(%.1f,%.1f) size=(%.1f×%.1f)\n",
+			bb.Min.X, bb.Min.Y, bb.Max.X, bb.Max.Y, w, h)
+
+		O := segs[0].A
+		D := geom.Sub(segs[0].B, segs[0].A)
+		if geom.Len(D) < 1e-9 && len(segs) > 1 {
+			O = segs[1].A
+			D = geom.Sub(segs[1].B, segs[1].A)
+		}
+		var left, right, splits, degens int
+		for _, s := range segs {
+			f, b := geom.SplitSeg(s, O, D)
+			if len(f) == 0 && len(b) == 0 {
+				degens++
+				continue
+			}
+			left += len(f)
+			right += len(b)
+			if len(f) > 0 && len(b) > 0 {
+				splits++
+			}
+		}
+		fmt.Printf("PROBE-SPLIT: O=(%.1f,%.1f) D=(%.1f,%.1f)\n", O.X, O.Y, D.X, D.Y)
+		fmt.Printf("PROBE-SPLIT: left=%d right=%d splits=%d degens=%d (EPS=%.1e)\n",
+			left, right, splits, degens, geom.EPS)
+
+		return
+	}
 }