bool FixedNumPoints::operator() (const Streamline<>& in, Streamline<>& out) const
{
// Perform an explicit calculation of streamline length
// From this, derive the spline position of each sample
assert (in.size() > 1);
out.clear();
out.index = in.index;
out.weight = in.weight;
value_type length = 0.0;
vector<value_type> steps;
for (size_t i = 1; i != in.size(); ++i) {
const value_type dist = (in[i] - in[i-1]).norm();
length += dist;
steps.push_back (dist);
}
steps.push_back (value_type(0));
Math::Hermite<value_type> interp (hermite_tension);
Streamline<> temp (in);
const size_t s = temp.size();
temp.insert (temp.begin(), temp[0] + (temp[0] - temp[ 1 ]));
temp.push_back ( temp[s] + (temp[s] - temp[s-1]));
value_type cumulative_length = value_type(0);
size_t input_index = 0;
for (size_t output_index = 0; output_index != num_points; ++output_index) {
const value_type target_length = length * output_index / value_type(num_points-1);
while (input_index < s && (cumulative_length + steps[input_index] < target_length))
cumulative_length += steps[input_index++];
if (input_index == s) {
out.push_back (temp[s]);
break;
}
const value_type mu = (target_length - cumulative_length) / steps[input_index];
interp.set (mu);
out.push_back (interp.value (temp[input_index], temp[input_index+1], temp[input_index+2], temp[input_index+3]));
}
return true;
}
Point<float> GMWMI_finder::find_interface (const std::vector< Point<float> >& tck, const bool end, Interp& interp) const
{
if (tck.size() == 0)
return Point<float>();
if (tck.size() == 1)
return tck.front();
if (tck.size() == 2)
return (end ? tck.back() : tck.front());
// Track is long enough; can do the proper search
// Need to generate an additional point beyond the end point
typedef Point<float> PointF;
size_t last = tck.size() - 1;
const PointF p_end (end ? tck.back() : tck.front());
const PointF p_prev (end ? tck[last-1] : tck[1]);
// Before proceeding, make sure that the interface lies somewhere in between these two points
if (interp.scanner (p_end))
return p_end;
const Tissues t_end (interp);
if (interp.scanner (p_prev))
return p_end;
const Tissues t_prev (interp);
if (! (((t_end.get_gm() > t_end.get_wm()) && (t_prev.get_gm() < t_prev.get_wm()))
|| ((t_end.get_gm() < t_end.get_wm()) && (t_prev.get_gm() > t_prev.get_wm())))) {
return p_end;
}
// Also make sure that the existing endpoint doesn't already obey the criterion
if (t_end.get_gm() - t_end.get_wm() < GMWMI_ACCURACY)
return p_end;
const PointF curvature (end ? ((tck[last]-tck[last-1]) - (tck[last-1]-tck[last-2])) : ((tck[0]-tck[1]) - (tck[1]-tck[2])));
const PointF extrap ((end ? (tck[last]-tck[last-1]) : (tck[0]-tck[1])) + curvature);
const PointF p_extrap (p_end + extrap);
Point<float> domain [4];
domain[0] = (end ? tck[last-2] : tck[2]);
domain[1] = p_prev;
domain[2] = p_end;
domain[3] = p_extrap;
Math::Hermite<float> hermite (GMWMI_HERMITE_TENSION);
float min_mu = 0.0, max_mu = 1.0;
Point<float> p_best = p_end;
size_t iters = 0;
do {
const float mu = 0.5 * (min_mu + max_mu);
hermite.set (mu);
const Point<float> p (hermite.value (domain));
interp.scanner (p);
const Tissues t (interp);
if (t.get_wm() > t.get_gm()) {
min_mu = mu;
} else {
max_mu = mu;
p_best = p;
if (t.get_gm() - t.get_wm() < GMWMI_ACCURACY)
return p_best;
}
} while (++iters != GMWMI_MAX_ITERS_TO_FIND_BOUNDARY);
return p_best;
}