Account for tile pixel start offset and size difference when calculating height on globe.

modules/globebrowsing/globes/renderableglobe.cpp

@@ -305,7 +305,12 @@ namespace globebrowsing {
         if (tile.status != Tile::Status::OK) {
             return 0;
         }
-        glm::vec2 transformedUv = uvTransform.uvOffset + uvTransform.uvScale * patchUV;
+        //glm::vec2 transformedUv = uvTransform.uvOffset + uvTransform.uvScale * patchUV;
+
+        glm::vec2 transformedUv = Tile::TileUvToTextureSamplePosition(
+            uvTransform,
+            patchUV,
+            glm::uvec2(tile.texture->dimensions()));
 
         // Sample and do linear interpolation
         // (could possibly be moved as a function in ghoul texture)

modules/globebrowsing/shaders/tile.hglsl

@@ -25,6 +25,12 @@
 #ifndef TEXTURETILE_HGLSL
 #define TEXTURETILE_HGLSL
 
+// Must match the values in tiledataset.cpp
+// (could be set as shader preprocessing data so that multiple definitions
+// are not needed)
+#define TILE_PIXEL_START_OFFSET ivec2(-2)
+#define TILE_PIXEL_SIZE_DIFFERENCE ivec2(4)
+
 vec4 patchBorderOverlay(vec2 uv, vec3 borderColor, float borderSize) {
 	vec2 uvOffset = uv - vec2(0.5);
 	float thres = 0.5 - borderSize/2;
@@ -83,7 +89,8 @@ vec2 compensateSourceTextureSampling(vec2 startOffset, vec2 sizeDiff, const Tile
 
 vec2 TileUVToTextureSamplePosition(const Tile tile, vec2 tileUV){
 	vec2 uv = tile.uvTransform.uvOffset + tile.uvTransform.uvScale * tileUV;
-	uv = compensateSourceTextureSampling(vec2(-2), vec2(4), tile, uv);
+	uv = compensateSourceTextureSampling(
+		TILE_PIXEL_START_OFFSET, TILE_PIXEL_SIZE_DIFFERENCE, tile, uv);
 	return uv;
 }
 

modules/globebrowsing/tile/tile.cpp

@@ -66,5 +66,30 @@ namespace globebrowsing {
         return tile;
     }
 
+    glm::vec2 Tile::compensateSourceTextureSampling(
+            glm::vec2 startOffset,
+            glm::vec2 sizeDiff,
+            glm::uvec2 resolution,
+            glm::vec2 tileUV) {
+        glm::vec2 sourceSize = glm::vec2(resolution) + sizeDiff;
+        glm::vec2 currentSize = glm::vec2(resolution);
+        glm::vec2 sourceToCurrentSize = currentSize / sourceSize;
+        tileUV = sourceToCurrentSize * (tileUV - startOffset / sourceSize);
+        return tileUV;
+    }
+
+     glm::vec2 Tile::TileUvToTextureSamplePosition(
+        const TileUvTransform uvTransform,
+        glm::vec2 tileUV,
+        glm::uvec2 resolution) {
+        glm::vec2 uv = uvTransform.uvOffset + uvTransform.uvScale * tileUV;
+        uv = compensateSourceTextureSampling(
+            TileDataset::tilePixelStartOffset,
+            TileDataset::tilePixelSizeDifference,
+            resolution,
+            uv);
+        return uv;
+    }
+
 } // namespace globebrowsing
-} // namespace openspace
+} // namespace openspace

modules/globebrowsing/tile/tile.h

@@ -32,6 +32,11 @@
 namespace openspace {
 namespace globebrowsing {
 
+    struct TileUvTransform {
+        glm::vec2 uvOffset;
+        glm::vec2 uvScale;
+    };
+
     using namespace ghoul::opengl;
 
     /**
@@ -84,6 +89,17 @@ namespace globebrowsing {
          */
         static Tile createPlainTile(const glm::uvec2& size, const glm::uvec4& color);
 
+        static glm::vec2 compensateSourceTextureSampling(
+                glm::vec2 startOffset,
+                glm::vec2 sizeDiff,
+                glm::uvec2 resolution,
+                glm::vec2 tileUV);
+
+        static glm::vec2 TileUvToTextureSamplePosition(
+            const TileUvTransform uvTransform,
+            glm::vec2 tileUV,
+            glm::uvec2 resolution);
+
         /**
         * A tile with status unavailable that any user can return to 
         * indicate that a tile was unavailable.

modules/globebrowsing/tile/tileselector.h

@@ -34,11 +34,6 @@
 namespace openspace {
 namespace globebrowsing {
 
-    struct TileUvTransform {
-        glm::vec2 uvOffset;
-        glm::vec2 uvScale;
-    };
-
     struct TileAndTransform {
         Tile tile;
         TileUvTransform uvTransform;