Add common functions for loading calibration with some error checking

From Bernd

include/msckf_vio/utils.h

@@ -0,0 +1,34 @@
+/*
+ * COPYRIGHT AND PERMISSION NOTICE
+ * Penn Software MSCKF_VIO
+ * Copyright (C) 2017 The Trustees of the University of Pennsylvania
+ * All rights reserved.
+ */
+
+#ifndef MSCKF_VIO_UTILS_H
+#define MSCKF_VIO_UTILS_H
+
+#include <ros/ros.h>
+#include <string>
+#include <opencv2/core/core.hpp>
+#include <Eigen/Geometry>
+
+namespace msckf_vio {
+/*
+ * @brief utilities for msckf_vio
+ */
+namespace utils {
+Eigen::Isometry3d getTransformEigen(const ros::NodeHandle &nh,
+                                    const std::string &field);
+
+cv::Mat getTransformCV(const ros::NodeHandle &nh,
+                       const std::string &field);
+
+cv::Mat getVec16Transform(const ros::NodeHandle &nh,
+                          const std::string &field);
+
+cv::Mat getKalibrStyleTransform(const ros::NodeHandle &nh,
+                                const std::string &field);
+}
+}
+#endif