StRoot: StBeamBackMaker/Line.cc Source File

00001 //
00002 // Pibero Djawotho <pibero@indiana.edu>
00003 // Indiana University Cyclotron Facility
00004 // 23 September 2005
00005 //
00006 
00007 // Local
00008 #include "Line.hh"
00009 
00010 Line::Line(const StThreeVectorD& o, const StThreeVectorD& d)
00011 {
00012   mOrigin = o;
00013   mDirection = d.unit();
00014 }
00015 
00016 StThreeVectorD Line::at(double pathlength) const
00017 {
00018   return mOrigin + pathlength * mDirection;
00019 }
00020 
00021 double Line::pathlength(const StThreeVectorD& point) const
00022 {
00023   return mDirection.dot(point - mOrigin);
00024 }
00025 
00026 StThreeVectorD Line::perigee(const StThreeVectorD& point) const
00027 {
00028   return at(pathlength(point));
00029 }
00030 
00031 StThreeVectorD Line::dca(const Line& line) const
00032 {
00033   double cosAngle = mDirection.dot(line.direction());
00034   double delta = cosAngle * cosAngle - 1;
00035   StThreeVectorD distance = mOrigin - line.origin();
00036   double pathlength = (distance.dot(mDirection) - cosAngle * distance.dot(line.direction())) / delta;
00037   double pathlength2 = (cosAngle * distance.dot(mDirection) - distance.dot(line.direction())) / delta;
00038   return at(pathlength) - line.at(pathlength2);
00039 }
00040 
00041 pair<double, double> Line::pathlengths(const Line& line) const
00042 {
00043   double cosAngle = mDirection.dot(line.direction());
00044   double delta = cosAngle * cosAngle - 1;
00045   double s = pathlength(line.origin());
00046   double t = line.pathlength(mOrigin);
00047   return make_pair(-(s + t * cosAngle) / delta, -(s * cosAngle + t) / delta);
00048 }