docs(#9): add some explanatory comments

src/potreeViewer.js

@@ -56,9 +56,11 @@ export async function createPotreeViewer(containerId, pointcloudUrl, settings) {
   pc.material.gradient = Potree.Gradients['VIRIDIS']
 
   e.pointcloud.projection = '+proj=geocent +datum=WGS84 +units=m +no_defs'
+
+  // Initialize camera position and target point (manually chosen)
   viewer.scene.view.setView(
-    [1993552.9, 87954.487, 7134018.721],
-    [1184471.63, 63828.49, 6243615.52]
+    [1993552.9, 87954.487, 7134018.721], // Initial camera position
+    [1184471.63, 63828.49, 6243615.52] // Initial target point
   )
 
   return viewer
@@ -96,20 +98,30 @@ function overrideShaderForGradient(pc) {
       /vec3 getElevation\(\)[\s\S]*?\}/,
       `
       vec3 getElevation(){
+          // Transform the vertex position into world coordinates
           vec4 world = modelMatrix * vec4(position, 1.0);
+
+          // Compute distance from Earth's center and latitude
           float radius = length(world.xyz);
           float latitude = asin(world.z / radius);
 
-          const float a = 6378137.0;
-          const float b = 6356752.3;
+          const float a = 6378137.0; // Equatorial radius
+          const float b = 6356752.3; // Polar radius
 
+          // Compute distance from Earth's center to the surface at the given latitude
           float cosLat = cos(latitude);
           float sinLat = sin(latitude);
           float numerator = (a*a * cosLat) * (a*a * cosLat) + (b*b * sinLat) * (b*b * sinLat);
           float denominator = (a * cosLat) * (a * cosLat) + (b * sinLat) * (b * sinLat);
           float radiusAtLatitude = sqrt(numerator / denominator);
 
-          float w = (radius - radiusAtLatitude - elevationRange.x) / (elevationRange.y - elevationRange.x);
+          // Compute depth below the ellipsoid (sea level)
+          float depth = radius - radiusAtLatitude;
+
+          // Normalize depth to a [0, 1] range for coloring
+          float w = (depth - elevationRange.x) / (elevationRange.y - elevationRange.x);
+
+          // Sample color from gradient texture based on normalized depth
           return texture2D(gradient, vec2(w, 1.0-w)).rgb;
       }
       `