Drawing a Line and a Point inside a Cube

ROOT
1

I am trying to draw a line (in a 3D box, so I can see all coordinates of that line) and, additionally, a point, to see how close that point is to that line.
With the code below, I can draw a line perfectly, but somehow the point only appears when the coordinates are positive (e.g. (“gP->SetPoint(0, 1.0, 0.0, 0.0);”). When I put the point at X = -1, the point does not appear anymore. Why is that?

Best regards,

Machiel

Main()
{
	c1 = new TCanvas("c1","",500,500);

	double xarr[2], yarr[2], zarr[2];

	xarr[0] = -4; yarr[0] = -4; zarr[0] = -4; 
	xarr[1] =  4; yarr[1] =  4; zarr[1] =  4; 

	TGraph2D* g = new TGraph2D(2, xarr, yarr, zarr);
	g->SetName("line");
	g->SetLineColor(kBlue);
	g->Draw("LINE");

	TGraph2D* gP = new TGraph2D(1);
	gP->SetName("point");
	gP->SetPoint(0, -1.0, 0.0, 0.0);
	gP->SetMarkerColor(kRed);
	gP->SetMarkerStyle(21);
	gP->SetMarkerSize(2);
	gP->Draw("P SAME");
}
2

TGraph2D does not work with one point only.
To draw one point try to use TPolyMarker3D

3

Thank you very much. This works.

4

To be complete, the TGraph2D class is closely linked to the Delaunay triangulation. So even 2 points is not good. We need at least 3 to make one triangle.