Bug in the DST Viewer: all tracks displayed wrongly starting from (0,0,0)

[dudarboh]

As we found out with @yradkhorrami, the DSTViewer displays tracks with a wrong position.

It uses reference point for x, y, z arguments of MarlinCED::drawHelix()

CEDViewer/src/DSTViewer.cc

Lines 231 to 234 in 0809ad2

	// start point
	float refx = 0.0;
	float refy = 0.0;
	float refz = 0.0;

CEDViewer/src/DSTViewer.cc

Lines 266 to 267 in 0809ad2

	MarlinCED::drawHelix(bField, charge, refx, refy, refz, px, py, pz, ml, size, color, 0.0, padLayout.getPlaneExtent()[1],
	gearTPC.getMaxDriftLength(), part->id() ); //hauke: add id

while by the design of the MarlinCED::drawHelix() there should go x, y, z coordinates ON the helix which is not the same...

See, e.g. how it is implemented inside DDCEDViewer, where x, y, z are calculated correctly from the reference point.

CEDViewer/src/DDCEDViewer.cc

Lines 1030 to 1039 in 0809ad2

	double Px = pt * std::cos( ts->getPhi() ) ;
	double Py = pt * std::sin( ts->getPhi() ) ;
	double Pz = pt * ts->getTanLambda() ;
	double Xs = ts->getReferencePoint()[0] - ts->getD0() * sin( ts->getPhi() ) ;
	double Ys = ts->getReferencePoint()[1] + ts->getD0() * cos( ts->getPhi() ) ;
	double Zs = ts->getReferencePoint()[2] + ts->getZ0() ;
	int helixColor = ( _useColorForHelixTracks ? color : 0xdddddd ) ;
	//helix
	DDMarlinCED::drawHelix(bField, charge, Xs, Ys, Zs, Px, Py, Pz, marker|(layer<<CED_LAYER_SHIFT), size/2*_scaleLineThickness,
	helixColor, 0.0, _helix_max_r, _helix_max_z, part->id() ); //hauke: add id

This results in the shifted track.
For the illustration, an example of such a track made by @yradkhorrami:

Red helix --- properly displayed position of the track
Green helix --- artificially starts at 0 because of the wrong input inside DSTViewer.