Add Snavely cost function

gtsam_unstable/nonlinear/tests/testExpression.cpp

@@ -271,6 +271,63 @@ struct Projective {
   }
 };
 
+// Templated pinhole camera model for used with Ceres. The camera is
+// parameterized using 9 parameters: 3 for rotation, 3 for translation, 1 for
+// focal length and 2 for radial distortion. The principal point is not modeled
+// (i.e. it is assumed be located at the image center).
+struct SnavelyReprojectionError {
+  SnavelyReprojectionError(double observed_x, double observed_y) :
+      observed_x(observed_x), observed_y(observed_y) {
+  }
+
+  template<typename T>
+  bool operator()(const T* const camera, const T* const point,
+      T* residuals) const {
+    // camera[0,1,2] are the angle-axis rotation.
+    T p[3];
+    ceres::AngleAxisRotatePoint(camera, point, p);
+
+    // camera[3,4,5] are the translation.
+    p[0] += camera[3];
+    p[1] += camera[4];
+    p[2] += camera[5];
+
+    // Compute the center of distortion. The sign change comes from
+    // the camera model that Noah Snavely's Bundler assumes, whereby
+    // the camera coordinate system has a negative z axis.
+    T xp = -p[0] / p[2];
+    T yp = -p[1] / p[2];
+
+    // Apply second and fourth order radial distortion.
+    const T& l1 = camera[7];
+    const T& l2 = camera[8];
+    T r2 = xp * xp + yp * yp;
+    T distortion = T(1.0) + r2 * (l1 + l2 * r2);
+
+    // Compute final projected point position.
+    const T& focal = camera[6];
+    T predicted_x = focal * distortion * xp;
+    T predicted_y = focal * distortion * yp;
+
+    // The error is the difference between the predicted and observed position.
+    residuals[0] = predicted_x - T(observed_x);
+    residuals[1] = predicted_y - T(observed_y);
+
+    return true;
+  }
+
+  // Factory to hide the construction of the CostFunction object from
+  // the client code.
+  static ceres::CostFunction* Create(const double observed_x,
+      const double observed_y) {
+    return (new ceres::AutoDiffCostFunction<SnavelyReprojectionError, 2, 9, 3>(
+        new SnavelyReprojectionError(observed_x, observed_y)));
+  }
+
+  double observed_x;
+  double observed_y;
+};
+
 /* ************************************************************************* */
 // manifold_traits prototype
 #include <boost/static_assert.hpp>