Append polygons in PolygonArray

edit

Hey there, I am new to this forum. I just discovered the possibility to display multiple polygons at once (in my case 2D x/y bounding boxes for a radar in RViz). In this case globally I have defined in Python:

   from jsk_recognition_msgs.msg import PolygonArray
   BB = PolygonArray()

When entering in my callback function, I have a series of if conditions thet get executed sequentially (I am decoding a series of messages from CAN Bus using cantools). So I have something like this:

def can_callback(data):
         if data.id ==  ..A
         elif data.id == ..B
         elif data.id == ..C
         elif data.id == ..D

When program enters the last if (elif data.id, n times as the number of objects detected by the radar), it evaluates for each enter the four vertices of the polygon I would like to visualize. After obtaining the four Vertices namely V1, V2, V3, V4 (Point32 with z coord = 0.0 ), I append to each condition of the if the Point. (by looking at the structure of PolygonArray: PolygonArray

This is what I try to assign in the if:

elif data.id == ..D       + entering with i= 0 !
        / do things/
        / obtain V1, V2, V3, V4 / 

         BB.polygons[i].polygon.points.append(V1)
         BB.polygons[i].polygon.points.append(V2)
         BB.polygons[i].polygon.points.append(V3)
         BB.polygons[i].polygon.points.append(V4)

         i=+ 1

I am getting as an error:

BB.polygons[i].polygon.points.append(V1) | IndexError: list index out of range

I don't know where I am getting things wrong, I don't have a clue on how to solve this. Any help is appreciated