From 454fbc00e2732484e1efd5a644bb4bea6011372f Mon Sep 17 00:00:00 2001
From: Benedikt Rothe <bene@hydrotec.de>
Date: Wed, 1 Oct 2025 18:43:46 +0200
Subject: [PATCH] Support High-Bit-detection for M-values (like for Z-values).
 Needed to read Geopackages-files, written by ESRI/ArcGISPro

---
 src/main/java/mil/nga/sf/wkb/GeometryReader.java | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/main/java/mil/nga/sf/wkb/GeometryReader.java b/src/main/java/mil/nga/sf/wkb/GeometryReader.java
index 6f9bb0e..8b2d9aa 100644
--- a/src/main/java/mil/nga/sf/wkb/GeometryReader.java
+++ b/src/main/java/mil/nga/sf/wkb/GeometryReader.java
@@ -35,6 +35,11 @@ public class GeometryReader {
 	 */
 	private static final long WKB25D = Long.decode("0x80000000");
 
+	/**
+	 * High-Bit-Indikator for M-values
+	 */
+	private static final long WKBM = Long.decode("0x40000000");
+
 	/**
 	 * Read a geometry from well-known bytes
 	 * 
@@ -355,6 +360,12 @@ public GeometryTypeInfo readGeometryType() throws IOException {
 			unsignedGeometryTypeCode -= WKB25D;
 		}
 
+		boolean hasM = false;
+		if (unsignedGeometryTypeCode > WKBM) {
+			hasM = true;
+			unsignedGeometryTypeCode -= WKBM;
+		}
+
 		int geometryTypeCode = (int) unsignedGeometryTypeCode;
 
 		// Determine the geometry type
@@ -366,7 +377,9 @@ public GeometryTypeInfo readGeometryType() throws IOException {
 		if (!hasZ) {
 			hasZ = GeometryCodes.hasZ(geometryTypeCode);
 		}
-		boolean hasM = GeometryCodes.hasM(geometryTypeCode);
+		if (!hasM) {
+			hasM = GeometryCodes.hasM(geometryTypeCode);
+		}
 
 		GeometryTypeInfo geometryInfo = new GeometryTypeInfo(geometryTypeCode,
 				geometryType, hasZ, hasM);