Fix missing edgecase inside Karney algorithm. Fixes #72

Author: dvdoug

CHANGELOG.md

@@ -1,8 +1,12 @@
 # Changelog
 
 ## [Unreleased]
+
+## [5.10.3] - 2025-01-31
 ### Changed
 - Updates to data for Canada and Germany
+### Fixed
+- Calculation of small distances along a meridian
 
 ## [5.10.2] - 2024-10-06
 ### Fixed
@@ -355,8 +359,9 @@ Initial release of this fork (based off of v2.3 of original)
  - Eastings and northings are rounded to 1m, and lat/long to 5dp (approx 1m) to avoid any misconceptions that precision is the same thing as accuracy.
  - When calculating surface distances, a more accurate mean radius is now used rather than that derived from historical definitions of a nautical mile
 
-[Unreleased]: https://github.com/dvdoug/PHPCoord/compare/v5.10.2..master
+[Unreleased]: https://github.com/dvdoug/PHPCoord/compare/v5.10.3..master
 
+[5.10.3]: https://github.com/dvdoug/PHPCoord/compare/v5.10.2..v5.10.3
 [5.10.2]: https://github.com/dvdoug/PHPCoord/compare/v5.10.1..v5.10.2
 [5.10.1]: https://github.com/dvdoug/PHPCoord/compare/v5.10.0..v5.10.1
 [5.10.0]: https://github.com/dvdoug/PHPCoord/compare/v5.9.2..v5.10.0

src/Geometry/Geodesic.php

@@ -385,6 +385,10 @@ public function distance(GeographicValue $from, GeographicValue $to): Length
                 $csig2,
                 $dn2,
             );
+
+            if ($sig12 < 1) {
+                $s12x *= $this->b;
+            }
         } elseif ($sbet1 == 0 && $lon12s >= $this->f * 180) {
             $s12x = $this->a * $lam12;
         } else {

tests/Point/GeographicPointTest.php

@@ -298,6 +298,14 @@ public function testDistanceIssue64(): void
         self::assertEqualsWithDelta(13917773.830057, $from->calculateDistance($to)->getValue(), 0.001);
     }
 
+    #[Group('distance')]
+    public function testIssue72(): void
+    {
+        $from = GeographicPoint::create(Geographic2D::fromSRID(Geographic2D::EPSG_WGS_84), new Degree(49.200221), new Degree(16.607841));
+        $to = GeographicPoint::create(Geographic2D::fromSRID(Geographic2D::EPSG_WGS_84), new Degree(49.204719), new Degree(16.607841));
+        self::assertEqualsWithDelta(500.239, $from->calculateDistance($to)->getValue(), 0.001);
+    }
+
     public function testGeographicGeocentric(): void
     {
         $from = GeographicPoint::create(Geographic3D::fromSRID(Geographic3D::EPSG_WGS_84), new Degree(53.80939444), new Degree(2.12955000), new Metre(73.0));