ROS image message encoding mono16

[lichunshang]

The Subscriber::imageCallback does not support mono16 encoding used in the TUM VIO dataset bag files. Images will end up looking like this:

when it should look like this:

okvis_ros/src/Subscriber.cpp

Lines 108 to 111 in bdc6db6

	{
	const cv::Mat raw(msg->height, msg->width, CV_8UC1,
	const_cast<uint8_t*>(&msg->data[0]), msg->step);

The solution is to use cv_bridge to make the conversion from ROS Image message to cv::Mat.

const cv::Mat raw = cv_bridge::toCvCopy(msg, "mono8")->image;

cv_bridge is already a dependency.

[tmako123]

In my case, I replaced

okvis_ros/src/okvis_node_synchronous.cpp

Lines 208 to 209 in bdc6db6

	cv::Mat filtered(msg1->height, msg1->width, CV_8UC1);
	memcpy(filtered.data, &msg1->data[0], msg1->height * msg1->width);

with

const cv::Mat filtered = cv_bridge::toCvCopy(msg1, "mono8")->image;