Better getPointResolution default when no transform available

[mike-000]

The default getPointResolution function does not give a meaningful result when proj4 is not used and there is no EPSG:4326 transform defined (as can be seen from the scalebar in https://codesandbox.io/s/wild-resonance-9350t) as the default identity transform is only meaningful when both projections units are degrees. This change is equivalent to having specified
getPointResolution: function (resolution) { return resolution; }
in the Projection options in that situation

Added a ScaleLine to the WMS without Projection example as it is now meaningful, although it may lack the 100% accuracy of the Single Image WMS with Proj4js or Custom Tiled WMS examples.

[ahocevar]

Not proceeding with transforms when toEPSG4326 equals the identityTransform is a good change, but I wonder why the whole change would not be as simple as

--- a/src/ol/proj.js
+++ b/src/ol/proj.js
@@ -202,16 +202,20 @@ export function getPointResolution(projection, resolution, point, opt_units) {
     }
   } else {
     const units = projection.getUnits();
-    if ((units == Units.DEGREES && !opt_units) || opt_units == Units.DEGREES) {
+    const toEPSG4326 = getTransformFromProjections(
+      projection,
+      get('EPSG:4326')
+    );
+    if (
+      toEPSG4326 === identityTransform ||
+      (units == Units.DEGREES && !opt_units) ||
+      opt_units == Units.DEGREES
+    ) {
       pointResolution = resolution;
     } else {
       // Estimate point resolution by transforming the center pixel to EPSG:4326,
       // measuring its width and height on the normal sphere, and taking the
       // average of the width and height.
-      const toEPSG4326 = getTransformFromProjections(
-        projection,
-        get('EPSG:4326')
-      );
       let vertices = [
         point[0] - resolution / 2,
         point[1],

Especially since you said

This change is equivalent to having specified
getPointResolution: function (resolution) { return resolution; }
in the Projection options in that situation

[mike-000]

That would not handle the case where opt_units is not degrees but is different to the projection units.

[ahocevar]

In this case I'd need tests to see what your intention and the expected results are.

[ahocevar]

Thanks, @mike-000