Added an angle field to image_dataset_metadata

dlib/data_io/image_dataset_metadata.cpp

@@ -78,6 +78,8 @@ namespace dlib
                         fout << " occluded='" << b.occluded << "'";
                     if (b.ignore)
                         fout << " ignore='" << b.ignore << "'";
+                    if (b.angle != 0)
+                        fout << " angle='" << b.angle << "'";
 
                     if (b.has_label() || b.parts.size() != 0)
                     {
@@ -189,6 +191,7 @@ namespace dlib
                         if (atts.is_in_list("truncated")) temp_box.truncated = sa = atts["truncated"];
                         if (atts.is_in_list("occluded"))  temp_box.occluded  = sa = atts["occluded"];
                         if (atts.is_in_list("ignore"))  temp_box.ignore  = sa = atts["ignore"];
+                        if (atts.is_in_list("angle"))  temp_box.angle  = sa = atts["angle"];
 
                         temp_box.rect.bottom() += temp_box.rect.top()-1;
                         temp_box.rect.right() += temp_box.rect.left()-1;

dlib/data_io/image_dataset_metadata.h

@@ -32,7 +32,8 @@ namespace dlib
                 difficult(false),
                 truncated(false),
                 occluded(false),
-                ignore(false)
+                ignore(false),
+                angle(0)
             {}
 
             rectangle rect;
@@ -46,6 +47,13 @@ namespace dlib
             bool occluded;
             bool ignore;
 
+            // The angle of the object in radians.  Positive values indicate that the
+            // object at the center of the box is rotated clockwise by angle radians.  A
+            // value of 0 would indicate that the object is in its "standard" upright pose.
+            // Therefore, to make the object appear upright we would have to rotate the
+            // image counter-clockwise by angle radians.
+            double angle; 
+
             bool has_label() const { return label.size() != 0; }
             /*!
                 ensures