// If closest point to us is farther than threshold,
// add point at midpoint

float threshold = 1;
int nearpts[] = pcfind(0, 'P', @P, /*maxdist*/1e20, /*numpt*/ 2);

// Nearest point is ourself, so we are interested in second
if (len(nearpts) > 1)
{
   int pt = nearpts[1];
   vector npos = point(0, 'P', pt);
   if (length(@P - npos) > threshold)
   {
      // Too far, add a point.
      vector midpoint = (npos + @P) / 2;
      addpoint(geoself(), midpoint);
   }
}