ReprojectRasterExtent: support single pixel input

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix implicitNotFound error and rename RGBAMethods implicit class [#3563](https://github.com/locationtech/geotrellis/pull/3563)
 - Set 'role' attribute in GDALMetadata tag written to tiff header, to match GDAL behaviour. [#3496](https://github.com/locationtech/geotrellis/issues/3496)
 - Avoid GeoAttrsError by using more robust target extent calculation [#3572](https://github.com/locationtech/geotrellis/pull/3572)
+- ReprojectRasterExtent: support single pixel input [#3573](https://github.com/locationtech/geotrellis/pull/3573)
 
 ## [3.7.1] - 2024-01-08
 

raster/src/main/scala/geotrellis/raster/reproject/ReprojectRasterExtent.scala

@@ -57,7 +57,9 @@ object ReprojectRasterExtent {
               val cols = ge.extent.width / ge.cellwidth
               val rows = ge.extent.height / ge.cellheight
               val pixelSize = distance / math.sqrt(cols * cols + rows * rows)
-              (pixelSize, pixelSize)
+              val pixelWidth = if(newExtent.width < 0.5 * pixelSize) newExtent.width else pixelSize
+              val pixelHeight = if(newExtent.height < 0.5*pixelSize) newExtent.height else pixelSize
+              (pixelWidth, pixelHeight)
           }
 
         val newCols = (newExtent.width / pixelSizeX + 0.5).toLong

raster/src/test/scala/geotrellis/raster/reproject/ReprojectRasterExtentSpec.scala

@@ -109,5 +109,13 @@ class ReprojectRasterExtentSpec extends AnyFunSpec
       assert(destinationRE.extent covers region)
       assert(destinationRE.extent.toPolygon() intersects region)
     }
+
+    it("should reproject single pixel extents") {
+      val inputExtent = GridExtent[Long](Extent(429180.0, 7652390.0, 429190.0, 7652400.0), CellSize(10.0, 10.0))
+      val destinationRE = ReprojectRasterExtent(inputExtent, CRS.fromEpsgCode(32639), LatLng)
+
+      assert(destinationRE.cols == 1)
+      assert(destinationRE.rows == 1)
+    }
   }
 }