Path analysis: own ground height ASL and highest point of the remote locator square (#133)

* Path analysis: own ground height ASL and highest point of the remote square

Two new settings in the path-analysis section of the Station tab:

- Own ground height ASL (stn_pathAnalysisOwnHeightAslMeters). Empty keeps
  the elevation model value at the own locator centre; a value from -500 to
  9000 m replaces the elevation of the first profile sample. The antenna
  height AGL is still added on top. The field commits on Enter or focus
  loss into the settings draft and reports a refused entry; it keeps the
  operator's spelling while that names the drafted number, because the
  draft is Compose state and would otherwise swap "25" for "25.0" under
  the cursor right after Enter.
- Target station on the highest point of its locator square
  (stn_pathAnalysisDxHighestPointInSquare, on by default). The remote square
  is sampled on a 5 x 5 grid of cell centres in one batched request against
  the Open-Meteo provider, the highest sample becomes the path end with its
  position and elevation. LocatorHighestPointResolver caches the result per
  locator for the session and backs off five minutes after a failure
  (failure list pruned and bounded); the analysis then falls back to the
  square centre and that result is not kept.

Both settings are drafted like the other path-analysis settings and take
effect with Apply/Close or Save; the reachability service reads the stored
values only.

The lookup runs on the reachability thread only. Building a request peeks
the resolver cache without blocking, so a cached square moves the endpoint
right away. The calculation key now includes the own height and the remote
ground elevation at full precision, and the switch, so changing either
recalculates.

Also assign the result of sanitizeEffectiveEarthRadiusFactor in the
PathAnalysisRequest constructor; it was called and dropped. No behaviour
change: the sanitizer is the identity for valid factors, and the analysis
service sanitizes again.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Document own ground height and highest-point setting of the path analysis

Changelog v1.50 (New), configuration and features pages in English and
German, and the terrain section of PROJECT_CONTEXT.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

github_docs/en-Configuration.md

@@ -68,13 +68,21 @@ The station map uses several values from the **Station** tab to calculate the te
 | Setting | Use |
 |---|---|
 | **Own antenna height AGL** | Height of the local antenna above the surrounding terrain in metres |
+| **Own ground height ASL, metres** | Optional: ground elevation of the own site above sea level. Leave empty to use the elevation model |
 | **Own TX power W** | Local transmit power in watts |
 | **Own ant. gain dBi** | Gain of the local antenna in dBi |
 | **DX OM TX power W** | Assumed transmit power of the remote station in watts |
 | **DX OM ant. gain dBi** | Assumed antenna gain of the remote station in dBi |
+| **Target station on the highest point of its locator square** | Ends the path at the highest point of the remote locator square instead of at its centre (on by default) |
 
 **AGL** means *Above Ground Level*. Do not enter the height above sea level. The terrain elevation at the local station already comes from the elevation profile; KST4Contest adds the configured antenna height to this value.
 
+This field is for the antenna height above ground only; the height of the site above sea level, if you want to set it, has its own field, described next.
+
+The elevation profile takes the local terrain elevation at the centre of the own locator square. If the actual site lies noticeably higher or lower, for example on a hill at the edge of the square, enter its ground elevation in **Own ground height ASL, metres** (**ASL**: *Above Sea Level*). KST4Contest then uses this value instead of the elevation model and still adds the antenna height on top. Values from -500 to 9000 metres are accepted. An empty field restores the elevation model. The own position on the map and in the profile remains the locator centre.
+
+A locator only tells which square a remote station is in, not where in it. Contest stations usually operate from the high ground of their square, so with **Target station on the highest point of its locator square** switched on, KST4Contest samples the remote square on a grid of 5 x 5 points, takes the highest of them and ends the path there, at that point's position and elevation. The lookup needs one request to the online elevation service per remote locator square; the result is kept until KST4Contest is closed. If the lookup fails, the analysis uses the centre of the square as before and tries again a few minutes later.
+
 For the remote station, KST4Contest currently uses a fixed antenna height of 10 metres above the local terrain. Its transmit power and antenna gain come from the two **DX OM** fields. These values are deliberately assumptions: ON4KST provides neither the actual antenna height nor the complete station data of the remote operator.
 
 Antenna gains must be entered in `dBi`. Add `2.15 dB` before entering a value specified in `dBd`: