diff --git a/common/g2d.h b/common/g2d.h
new file mode 100644
index 0000000..21c21ac
--- /dev/null
+++ b/common/g2d.h
@@ -0,0 +1,124 @@
+/* Copyright (C) 2013-2016, The Regents of The University of Michigan.
+All rights reserved.
+This software was developed in the APRIL Robotics Lab under the
+direction of Edwin Olson, ebolson@umich.edu. This software may be
+available under alternative licensing terms; contact the address above.
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+The views and conclusions contained in the software and documentation are those
+of the authors and should not be interpreted as representing official policies,
+either expressed or implied, of the Regents of The University of Michigan.
+*/
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "zarray.h"
+
+// This library tries to avoid needless proliferation of types.
+//
+// A point is a double[2]. (Note that when passing a double[2] as an
+// argument, it is passed by pointer, not by value.)
+//
+// A polygon is a zarray_t of double[2]. (Note that in this case, the
+// zarray contains the actual vertex data, and not merely a pointer to
+// some other data. IMPORTANT: A polygon must be specified in CCW
+// order.  It is implicitly closed (do not list the same point at the
+// beginning at the end.
+//
+// Where sensible, it is assumed that objects should be allocated
+// sparingly; consequently "init" style methods, rather than "create"
+// methods are used.
+
+////////////////////////////////////////////////////////////////////
+// Lines
+
+typedef struct
+{
+    // Internal representation: a point that the line goes through (p) and
+    // the direction of the line (u).
+    double p[2];
+    double u[2]; // always a unit vector
+} g2d_line_t;
+
+// initialize a line object.
+void g2d_line_init_from_points(g2d_line_t *line, const double p0[2], const double p1[2]);
+
+// The line defines a one-dimensional coordinate system whose origin
+// is p. Where is q? (If q is not on the line, the point nearest q is
+// returned.
+double g2d_line_get_coordinate(const g2d_line_t *line, const double q[2]);
+
+// Intersect two lines. The intersection, if it exists, is written to
+// p (if not NULL), and 1 is returned. Else, zero is returned.
+int g2d_line_intersect_line(const g2d_line_t *linea, const g2d_line_t *lineb, double *p);
+
+////////////////////////////////////////////////////////////////////
+// Line Segments. line.p is always one endpoint; p1 is the other
+// endpoint.
+typedef struct
+{
+    g2d_line_t line;
+    double p1[2];
+} g2d_line_segment_t;
+
+void g2d_line_segment_init_from_points(g2d_line_segment_t *seg, const double p0[2], const double p1[2]);
+
+// Intersect two segments. The intersection, if it exists, is written
+// to p (if not NULL), and 1 is returned. Else, zero is returned.
+int g2d_line_segment_intersect_segment(const g2d_line_segment_t *sega, const g2d_line_segment_t *segb, double *p);
+
+void g2d_line_segment_closest_point(const g2d_line_segment_t *seg, const double *q, double *p);
+double g2d_line_segment_closest_point_distance(const g2d_line_segment_t *seg, const double *q);
+
+////////////////////////////////////////////////////////////////////
+// Polygons
+
+zarray_t *g2d_polygon_create_data(double v[][2], int sz);
+
+zarray_t *g2d_polygon_create_zeros(int sz);
+
+zarray_t *g2d_polygon_create_empty();
+
+void g2d_polygon_add(zarray_t *poly, double v[2]);
+
+// Takes a polygon in either CW or CCW and modifies it (if necessary)
+// to be CCW.
+void g2d_polygon_make_ccw(zarray_t *poly);
+
+// Return 1 if point q lies within poly.
+int g2d_polygon_contains_point(const zarray_t *poly, double q[2]);
+
+// Do the edges of the polygons cross? (Does not test for containment).
+int g2d_polygon_intersects_polygon(const zarray_t *polya, const zarray_t *polyb);
+
+// Does polya completely contain polyb?
+int g2d_polygon_contains_polygon(const zarray_t *polya, const zarray_t *polyb);
+
+// Is there some point which is in both polya and polyb?
+int g2d_polygon_overlaps_polygon(const zarray_t *polya, const zarray_t *polyb);
+
+// returns the number of points written to x. see comments.
+int g2d_polygon_rasterize(const zarray_t *poly, double y, double *x);
+
+#ifdef __cplusplus
+}
+#endif