Added a get_num_dimensions() method to the hog_image.

dlib/image_keypoint/hog.h

@@ -91,6 +91,12 @@ namespace dlib
         inline long nc (
         ) const { return num_block_cols; }
 
+        long get_num_dimensions (
+        ) const
+        {
+            return block_size*block_size*num_orientation_bins;
+        }
+
         inline const descriptor_type& operator() (
             long row,
             long col

dlib/image_keypoint/hog_abstract.h

@@ -168,6 +168,15 @@ namespace dlib
                 - returns the number of columns in this HOG image
         !*/
 
+        long get_num_dimensions (
+        ) const;
+        /*!
+            ensures
+                - returns the number of dimensions in the feature vectors generated by
+                  this object.  
+                - In particular, returns the value block_size*block_size*num_orientation_bins
+        !*/
+
         inline const descriptor_type& operator() (
             long row,
             long col
@@ -180,7 +189,7 @@ namespace dlib
                 - returns the descriptor for the HOG block at the given row and column.  This descriptor 
                   will include information from a window that is located at get_block_rect(row,col) in
                   the original image given to load().
-                - The returned descriptor vector will have block_size*block_size*num_orientation_bins elements.
+                - The returned descriptor vector will have get_num_dimensions() elements.
         !*/
 
         const rectangle get_block_rect (