Surveying

Moved here from https://github.com/nervosys/AutonomySim/wiki/Implementing-a-Drone-Survey-script

Ever wanted to capture a bunch of top-down pictures of a certain location? Well, the Python API makes this really simple. See the code available here.

Let's assume we want the following variables:

Variable	Description
boxsize	The overall size of the square box to survey
stripewidth	How far apart to drive the swim lanes, this can depend on the type of camera lens, for example.
altitude	The height to fly the survey.
speed	The speed of the survey can depend on how fast your camera can snap shots.

So with these we can compute a square path box using this code:

path = []
distance = 0
while x < self.boxsize:
    distance += self.boxsize
    path.append(Vector3r(x, self.boxsize, z))
    x += self.stripewidth
    distance += self.stripewidth
    path.append(Vector3r(x, self.boxsize, z))
    distance += self.boxsize
    path.append(Vector3r(x, -self.boxsize, z))
    x += self.stripewidth
    distance += self.stripewidth
    path.append(Vector3r(x, -self.boxsize, z))
    distance += self.boxsize

Assuming we start in the corner of the box, increment x by the stripe width, then fly the full y-dimension of -boxsize to +boxsize, so in this case, boxsize is half the size of the actual box we will be covering.

Once we have this list of Vector3r objects, we can fly this path very simply with the following call:

result = self.client.moveOnPath(
    path, self.velocity, trip_time, DrivetrainType.ForwardOnly, YawMode(False,0), lookahead, 1)

We can compute an appropriate trip_time timeout by dividing the distance of the path and the speed we are flying.

The lookahead needed here for smooth path interpolation can be computed from the velocity using self.velocity + (self.velocity/2). The more lookahead, the smoother the turns. This is why you see in the screenshot that the ends of each swimland are smooth turns rather than a square box pattern. This can result in a smoother video from your camera also.

That's it. Pretty simple, huh?

Of course, we can add a lot more intelligence to this, make it avoid known obstacles on the map, make it climb up and down a hillside so you can survey a slope, etc. This is only the tip of the iceberg in terms of what is possible.