Cherry-picked devlop fixes into 2.4:

Fixed warning in Release mode
 Added default constructor
 Added .gitignore with build directory in there
 Disabled GTSAM_USE_SYSTEM_EIGEN flag until patches are incorporated into Eigen

.gitignore

@@ -0,0 +1 @@
+/build/

CMakeLists.txt

@@ -130,7 +130,12 @@ endif()
 
 ###############################################################################
 # Option for using system Eigen or GTSAM-bundled Eigen
-option(GTSAM_USE_SYSTEM_EIGEN "Find and use system-installed Eigen. If 'off', use the one bundled with GTSAM" OFF)
+### Disabled until our patches are included in Eigen ###
+### See:  http://eigen.tuxfamily.org/bz/show_bug.cgi?id=704 (Householder QR MKL selection)
+###       http://eigen.tuxfamily.org/bz/show_bug.cgi?id=705 (Fix MKL LLT return code)
+###       http://eigen.tuxfamily.org/bz/show_bug.cgi?id=716 (Improved comma initialization)
+# option(GTSAM_USE_SYSTEM_EIGEN "Find and use system-installed Eigen. If 'off', use the one bundled with GTSAM" OFF)
+set(GTSAM_USE_SYSTEM_EIGEN OFF)
 
 # Switch for using system Eigen or GTSAM-bundled Eigen
 if(GTSAM_USE_SYSTEM_EIGEN)

gtsam/geometry/EssentialMatrix.h

@@ -38,6 +38,11 @@ public:
   /// @name Constructors and named constructors
   /// @{
 
+  /// Default constructor
+  EssentialMatrix() :
+      aTb_(1, 0, 0), E_(aTb_.skew()) {
+  }
+
   /// Construct from rotation and translation
   EssentialMatrix(const Rot3& aRb, const Sphere2& aTb) :
       aRb_(aRb), aTb_(aTb), E_(aTb_.skew() * aRb_.matrix()) {

gtsam/geometry/Sphere2.cpp

@@ -108,8 +108,7 @@ Vector Sphere2::localCoordinates(const Sphere2& y) const {
 
   // Make sure that the angle different between x and y is less than 90. Otherwise,
   // we can project x + xi_hat from the tangent space at x to y.
-  double cosAngle = y.p_.dot(p_);
+  assert(y.p_.dot(p_) > 0.0 && "Can not retract from x to y.");
-  assert(cosAngle > 0.0 && "Can not retract from x to y.");
 
   // Get the basis matrix
   Matrix B = basis();