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[dharmon <>]

I figured this out, so I thought I would share here for posterity.

First, you have to get access to the Point_1 (or Point_2 or Point_3)
structure from the active objects table:

Point_1 pt = *tr.active_points_1_table_handle().at(Point_key(id));

id is the unsigned id of the point of interest. The x() method of Point_1
returns a polynomial whose coefficients can be accessed using the []
operator.

By default, the KDS uses exact arithmetic, so to do something with it you
want to convert it to double using CGAL's built-in conversion tools:

double x = CGAL::to_double(pt.x()[0]);
double v = CGAL::to_double(pt.x()[1]);

For linear trajectories, the above is sufficient to get the point's
positions at all times, x+v*t. Now, one key thing is that the stored
positions are based at t=0. so if t_curr is the current time, the current
position is actually,

double x_curr = x + v * t_curr;

It is not just x. From this, you can figure out how to adjust x and v for
impulse changes in velocity.

double x_new = (x + v * t_curr) - v_new * t_curr;
// Construct new Point_1 from (x_new,v_new)
*tr.active_points_1_table_handle().set(pt_new);

That's it. For Point_2 there is a y() method that gives the polynomial
describing the y-coordinate trajectory. Similarly, Point_3 has a z() method.

Hopefully someone finds this helpful.



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