uv_coordinates.rb in tracksperanto-3.0.0

- old
+ new
@@ -1,23 +1,25 @@
 # -*- encoding : utf-8 -*-
-# Syntheyes and some other apps use a relative UV coordinate sustem. For Syntheyes, zero is at the
-# optical center of the image, and goes positive right and up. Since Tracksperanto works in absolute
-# pixels we need to convert to and fro.
+# For Syntheyes, zero is at the
+# optical center of the image, and goes positive right and up. The corners get the [-1..1] coordinates
+# respectively. Since Tracksperanto works in absolute pixels we need to convert to and from these cords.
+# Note that Syntheyes actually assumes the center of the first pixel to be at -1,1 so a small
+# adjustment is necessary to maintain subpixel accuracy.
 module Tracksperanto::UVCoordinates
   
-  # UV coords used by Syntheyes and it's lens distortion algos.
+  # Convert absoilute X and Y values off the BL corner into Syntheyes UV coordinates
   def absolute_to_uv(abs_x, abs_y, w, h)
     [convert_to_uv(abs_x, w), convert_to_uv(abs_y, h) * -1]
   end
   
-  def convert_to_uv(absolute_value, absolute_side)
-    x = (absolute_value / absolute_side.to_f) - 0.5
-    # .2 to -.3, y is reversed and coords are double
-    x * 2
+  # Convert absoilute pixel value off the BL corner into Syntheyes UV coordinate
+  def convert_to_uv(abs_value, absolute_side)
+    uv_value = (((abs_value.to_f - 0.5) / (absolute_side.to_f - 1)) - 0.5) * 2.0
   end
-  
-  def convert_from_uv(absolute_side, uv_value)
-    # First, start from zero (-.1 becomes .4)
-    value_off_corner = (uv_value.to_f / 2) + 0.5
-    absolute_side * value_off_corner
+
+  # Convert Syntheyes UV value into absoilute pixel value off the BL corner
+  def convert_from_uv(uv_value, absolute_side)
+    # Account for the fact that Syntheyes assumes the
+    # pixel values to be at the center of the pixel
+    abs_value = (((uv_value.to_f / 2.0) + 0.5) * (absolute_side.to_f - 1)) + 0.5
   end
 end