diff --git a/src/OffscreenContextNULL.cc b/src/OffscreenContextNULL.cc
new file mode 100644
index 00000000..bcf9ff66
--- /dev/null
+++ b/src/OffscreenContextNULL.cc
@@ -0,0 +1,66 @@
+/*
+
+Create an NULL OpenGL context that doesnt actually use any OpenGL code,
+and can be compiled on a system without OpenGL.
+
+*/
+
+#include <vector>
+
+#include "OffscreenContext.h"
+#include "printutils.h"
+#include "imageutils.h"
+
+#include <map>
+#include <string>
+#include <sstream>
+
+using namespace std;
+
+struct OffscreenContext
+{
+  int width;
+  int height;
+};
+
+void offscreen_context_init(OffscreenContext &ctx, int width, int height)
+{
+  ctx.width = width;
+  ctx.height = height;
+}
+
+string offscreen_context_getinfo(OffscreenContext *ctx)
+{
+  return string("NULLGL");
+}
+
+OffscreenContext *create_offscreen_context(int w, int h)
+{
+  OffscreenContext *ctx = new OffscreenContext;
+  offscreen_context_init( *ctx, w, h );
+}
+
+bool teardown_offscreen_context(OffscreenContext *ctx)
+{
+  return true;
+}
+
+bool save_framebuffer(OffscreenContext *ctx, char const * filename)
+{
+        std::ofstream fstream(filename,std::ios::out|std::ios::binary);
+        if (!fstream.is_open()) {
+                std::cerr << "Can't open file " << filename << " for writing";
+                return false;
+        } else {
+                save_framebuffer(ctx, fstream);
+                fstream.close();
+        }
+        return true;
+}
+
+bool save_framebuffer(OffscreenContext *ctx, std::ostream &output)
+{
+  output << "NULLGL framebuffer";
+  return true;
+}
+
diff --git a/src/grid.h b/src/grid.h
index c6cc7d25..913623c7 100644
--- a/src/grid.h
+++ b/src/grid.h
@@ -11,8 +11,14 @@ typedef __int64 int64_t;
 #include <boost/unordered_map.hpp>
 #include <utility>
 
-const double GRID_COARSE = 0.001;
-const double GRID_FINE   = 0.000001;
+//const double GRID_COARSE = 0.001;
+//const double GRID_FINE   = 0.000001;
+/* Using decimals that are exactly convertible to binary floating point
+(and then converted exactly to GMPQ Rational in CGAL's engine) provides
+at least a 5% speedup for ctest -R CGAL. We choose 1/1024 and 1/(1024*1024)
+In python: print '%.64f' % float(fractions.Fraction(1,1024)) */
+const double GRID_COARSE = 0.0009765625;
+const double GRID_FINE   = 0.00000095367431640625;
 
 template <typename T>
 class Grid2d