Support wide-angle and depth cameras in MultiCameraSensor

[scpeters]

It looks like the MultiCameraSensor does not support wide-angle cameras. Currently a single wide-angle camera can be created by using sdf <sensor type ='wideanglecamera'. That xml attribute is matched against the strings used in the GZ_REGISTER_STATIC_SENSOR macro (see WideAngleCameraSensor's macro for example). Currently, that sensor type attribute is the only way to indicate that a wideanglecamera sensor should be used (see example in lensflare_plugin.world). During WideAngleCameraSensor::Init, it calls Scene::CreateWideAngleCamera.

A MultiCameraSensor uses the "multicamera" type attribute string and creates sub-cameras based on the contents of multiple <camera> blocks within the <sensor> (see example in lensflare_plugin.world). During MultiCameraSensor::Init, it calls Scene::CreateCamera for each <camera> block that it finds. In order for MultiCameraSensor to contain wide-angle cameras, it would need some logic that allows it to call Scene::CreateWideAngleCamera, but we currently don't have a way to specify that, since the sensor type attribute is already set to "multicamera".

[scpeters]

Perhaps a //camera/@type attribute would be the right way to specify this to allow MultiCameraSensor to hold cameras of different types. It may take some refactoring of the gazebo sensor classes

[kjeppesen1]

I added the camera type attribute to the camera.sdf file on the camera_type_attribute_6 branch on my fork. Brief testing seems to prove that this attribute is recognized when calling GetAttribute("type").

However, in discussion with @scpeters it seems that there are some larger architectural issues preventing the use of both wideanglecamera and depthcamera within the multicamera sensor. When adding an openni_kinect gazebo_ros plugin to the multicamera sensor, gazebo crashes and produces the following error:

Thread 1 "gzserver" received signal SIGSEGV, Segmentation fault. 0x00007fff57cc4e07 in gazebo::DepthCameraPlugin::Load(std::shared_ptr, std::shared_ptr) () from /usr/lib/x86_64-linux-gnu/gazebo-9/plugins/libDepthCameraPlugin.so (gdb)

My multi_cam_type branch on my gazebo fork demonstrates this issue when run with the included multi_camera.world. The error seems to be related to the mismatch between rendering::CameraPtr and rendering::DepthCameraPtr, as well as the sensor type not being "depth." Note that this code forces the creation of a depth camera regardless of the camera type, although some logic that creates the correct camera based on the type attribute is included as comments.

[scpeters]

Per our previous discussion and debugging session, @kjeppesen1 was attempting to use his fork of gazebo with a MultiCameraSensor modified to contain multiple depth cameras. He was also attempting to use the DepthCameraPlugin with these embedded depth sensors. There is a problem, though, because the DepthCameraPlugin expects to be attached to a DepthCameraSensor.