Add camera frustum display and DEM painter

[Ryanf55]

Desired behavior

Implement a way to display the camera frustum and also paint the DEM terrain where the camera is facing.

This is useful for simulation of aerial vehicles with downward facing cameras or other directional sensors.

Alternatives considered

• Switch simulators to Cesium or another tool that supports it

Implementation suggestion

• Add a wireframe to view the frustum of the camera
• Add ability to shade the ground where the camera is pointing

Examples

• https://webglfundamentals.org/webgl/lessons/webgl-visualizing-the-camera.html
• https://answers.ros.org/question/410027/drawing-camera-frustum-in-rviz-using-tf-and-visualization-marker/
• https://gis.stackexchange.com/questions/330787/drawing-camera-lines-until-frustum-rectangle-using-cesium
• Support real time image / sensor draping onto terrain  goodrobots/MAVCesium#13
• https://canberrauav.github.io/cuav/build/html/index.html

Additional context

• Similar to Image visualization / LED Strip gz-sensors#427

[scpeters]

a camera frustum was displayed as part of the gazebo-classic CameraVisual (see screenshots from the camera distortion tutorial), but it's size wasn't based on the actual field of view (see hard-coded parameters in CameraVisual.cc)

From a brief discussion with @iche033, it shouldn't be too hard to render a frustum for the camera, though it would be more involved to render camera images in a frame at the end of the frustum as was done in gazebo-classic

[scpeters]

From a brief discussion with @iche033, it shouldn't be too hard to render a frustum for the camera, though it would be more involved to render camera images in a frame at the end of the frustum as was done in gazebo-classic

more from @iche033:

• we could enable camera visualization by adding a gui plugin similar to the visualize_lidar plugin
• we would also need a gz::rendering::CameraVisual object
• the gui plugin would get the frustum from the camera sensor and create the gz::rendering::CameraVisual object

[scpeters]

related: a feature request for camera image visualization gazebosim/gz-sensors#427