update draw line and shape

www/map-geo.js

@@ -25,6 +25,20 @@
     return res > 0 ? 1 / res : 20;
   }
 
+  /** Centimetres → image pixels (uses map resolution m/px). */
+  function cmToPixels(cm, map) {
+    const res = meta(map).resolution;
+    if (!Number.isFinite(Number(cm)) || res <= 0) return 0;
+    return Number(cm) / 100 / res;
+  }
+
+  /** Image pixels → centimetres. */
+  function pixelsToCm(px, map) {
+    const res = meta(map).resolution;
+    if (!Number.isFinite(Number(px)) || res <= 0) return 0;
+    return Number(px) * res * 100;
+  }
+
   function imageSize(map, imageEl) {
     const w = imageEl?.naturalWidth || meta(map).width || 0;
     const h = imageEl?.naturalHeight || meta(map).height || 0;
@@ -143,6 +157,8 @@
   window.MapGeo = {
     meta,
     pixelsPerMeter,
+    cmToPixels,
+    pixelsToCm,
     imageSize,
     createView,
     applyViewTransform,