diff --git a/aos/vision/blob/contour.h b/aos/vision/blob/contour.h
new file mode 100644
index 0000000..9cd1400
--- /dev/null
+++ b/aos/vision/blob/contour.h
@@ -0,0 +1,40 @@
+#ifndef _AOS_VIISON_BLOB_CONTOUR_H_
+#define _AOS_VIISON_BLOB_CONTOUR_H_
+
+#include "aos/vision/blob/range_image.h"
+#include "aos/vision/blob/region_alloc.h"
+
+namespace aos {
+namespace vision {
+
+// Countour nodes are slingly linked list chains of pixels that go around
+// the boundary of a blob.
+struct ContourNode {
+  ContourNode(int x, int y) : pt({x, y}) { next = this; }
+  ContourNode(int x, int y, ContourNode *next) : pt({x, y}), next(next) {}
+  ContourNode() {}
+
+  // Construction routine to attach a node to the end.
+  // Prefer to manipulate contours using RangeImgToContour.
+  ContourNode *append(int x, int y, AnalysisAllocator *alloc) {
+    next = alloc->cons_obj<ContourNode>(x, y);
+    return next;
+  }
+  // Construction routine to attach a node to the beginning.
+  // Prefer to manipulate contours using RangeImgToContour.
+  ContourNode *pappend(int x, int y, AnalysisAllocator *alloc) {
+    return alloc->cons_obj<ContourNode>(x, y, this);
+  }
+
+  Point pt;
+  ContourNode *next;
+};
+
+// Converts range image to contour using sweepline analysis.
+ContourNode *RangeImgToContour(const RangeImage &rimg,
+                               AnalysisAllocator *alloc);
+
+}  // namespace vision
+}  // namespace aos
+
+#endif  //  _AOS_VIISON_BLOB_CONTOUR_H_