diff --git a/gtsam/geometry/Cal3Bundler.h b/gtsam/geometry/Cal3Bundler.h
index fff9a6e6d..e508710cd 100644
--- a/gtsam/geometry/Cal3Bundler.h
+++ b/gtsam/geometry/Cal3Bundler.h
@@ -36,6 +36,8 @@ private:
   double u0_, v0_; ///< image center, not a parameter to be optimized but a constant
 
 public:
+  /// dimension of the variable - used to autodetect sizes
+  static const size_t dimension = 3;
 
   /// @name Standard Constructors
   /// @{
diff --git a/gtsam/geometry/Cal3DS2.h b/gtsam/geometry/Cal3DS2.h
index 51fe958d6..82bfa4c5f 100644
--- a/gtsam/geometry/Cal3DS2.h
+++ b/gtsam/geometry/Cal3DS2.h
@@ -46,6 +46,9 @@ protected:
   double p1_, p2_ ; // tangential distortion
 
 public:
+  /// dimension of the variable - used to autodetect sizes
+  static const size_t dimension = 9;
+
   Matrix K() const ;
   Eigen::Vector4d k() const { return Eigen::Vector4d(k1_, k2_, p1_, p2_); }
   Vector vector() const ;
diff --git a/gtsam/geometry/Cal3Unified.h b/gtsam/geometry/Cal3Unified.h
index 58e024c27..eacbf7053 100644
--- a/gtsam/geometry/Cal3Unified.h
+++ b/gtsam/geometry/Cal3Unified.h
@@ -50,8 +50,9 @@ private:
   double xi_;  // mirror parameter
 
 public:
-  //Matrix K() const ;
-  //Eigen::Vector4d k() const { return Base::k(); }
+  /// dimension of the variable - used to autodetect sizes
+  static const size_t dimension = 10;
+
   Vector vector() const ;
 
   /// @name Standard Constructors