Merge pull request #1114 from szekerest/scalebar-geodesic-measurement-update3

Document automatic geodesic scalebar measurement (#7397)

Author: szekerest

en/mapfile/scalebar.txt

@@ -9,9 +9,14 @@
 
  .. note::
 
-    MapServer supports only cartesian distances (straight-line distance measured
-    on a flat surface), it does not convert distances into an ellipsoidal 
-    distance (measured on a spherical shape).
+    Starting with MapServer 9.0, when the map has a declared CRS, scalebar
+    distances are measured geodesically on its ellipsoid using a horizontal
+    sample centered on the map. The result represents the local horizontal
+    scale at the map center and may differ from scalebars rendered by earlier
+    releases, especially in distorted projections. Maps without a CRS retain
+    Cartesian measurement. If a declared CRS cannot be used for geodesic
+    measurement, scalebar rendering fails instead of falling back to Cartesian
+    measurement.
 
 Scalebars currently do not make use of TrueType fonts. The size of the 
 scalebar image is NOT known prior to rendering, so be careful not to 

en/utilities/scalebar.txt

@@ -9,9 +9,14 @@
 
  .. note::
 
-    MapServer supports only cartesian distances (straight-line distance measured
-    on a flat surface), it does not convert distances into an ellipsoidal 
-    distance (measured on a spherical shape).
+    Starting with MapServer 9.0, when the map has a declared CRS, scalebar
+    distances are measured geodesically on its ellipsoid using a horizontal
+    sample centered on the map. The result represents the local horizontal
+    scale at the map center and may differ from scalebars rendered by earlier
+    releases, especially in distorted projections. Maps without a CRS retain
+    Cartesian measurement. If a declared CRS cannot be used for geodesic
+    measurement, scalebar rendering fails instead of falling back to Cartesian
+    measurement.
 
 Purpose
 -------