Streets of Coverage, Morphing Polygon with Reference Points

CesiumJS
1

I am trying to create a street of coverage swath across a region, and at each time instant have the polygon vertecies requiered to construct it.

The problem is that as this coverage swath grows more verticies are added to kind of extrude that shape along the natural street polygon it creates as the satellite above continues its orbit.

Where making the current swath (or polygon representing what the satellite can see at a given time) is simple with reference verticies since they stay consistent, here I’m having a problem.

If I were not to use reference points, then I would have potentially thousands of separate polygons, all with say one-second durations. I feel like that would be too much to run.

My original idea is to see which state has the most vertices in my long swath, then at every time instance, use that number of vertices. So at the start, when there would be fewer, I would double (or even triple) up on a point.

Is there an easier way to have a shifting polygon over time with a growing number of vertices?

Thank you.

2

Hi @Caleb_Arbreton, have you looked at the European Space Agency’s Orbit Prediction Tool? It uses Cesium to visualize both the path and the instrument footprint.

I don’t quite understand what you are trying to do. What is the start and end time of the swath you are trying to visualize? Would it make sense to have a single rectangle, which then drags along the surface behind the satellite (via translations or similar)? This would show the coverage for a constant-length interval of time, before the current animation time.

3

Hello @jjhembd, I have not come across the tool, but it may be worth looking into.

If you were to imagine the Region of Interest as the canvas, over which the camera might paint its sight swath, then the final polygon would be the one that represents one full pass over that RoI.

The reason using a rectangle that expands wouldn’t work for my purposes is that the swath itself may not be straight if the sensor were to slew during its pass over the RoI.

All this to say what I’d like to be able to do would be almost akin to those balloon animal balloons. I’d know the maximum number of vertices as the amount required for the final state (when the camera has finished looking at the RoI, or the perverbial brush-stroke is at its longest), but the first instance would be the smallest with just the first dab of “paint” on the RoI. The way I’m considering it is similar to how there’d be the most latex on the tip of the balloon to allow it to expand as it grows larger, this being analogous to repeated vertices.

So say I had points on a square with vertices (0,0),(1,0),(1,0),(1,1),(1,1),(0,1). It is clear that two of these are repeated, but as this square continues its swath, the vertices may change to something like

(0,0),(1,0),(2,1),(2,2),(1,1),(0,1). This is an example of just expanding once, but the pattern could be repeated again if you were to extrude that right edge to the right and any direction up or down again.

Also in this example, I started with a square and ended with another polygon. It would seem more intensive to create two polygons (each with one second durations) than to create one polygon with 6 vertices instead of 4, and have some vertices overlap to begin with, so I can use them to extrude later. Then these vertices would become reference points that the polygon could be constructed using.

Hopefully that makes sense. I’d like the easiest way to draw an expanding polygon that has an apparent growing number of vertices.