I am not sure what are the “coordinates of the projection” in your mind… May be you should just use GetXaxis() on the histogram and use the getter(s) you need, there is many. See the TAxis doc.

I’m probably blind because looked through the gets and can’t see how to get the x coordinate for a y coordinate on the curve. I think my solution is too complicated to do this look through all the bins and see which one is closest.

Something like:

for i in range(0,projX.GetNbinsX()/2):
... try:
... npt.assert_almost_equal(projX.GetBinContent(i), yCoordinate, decimal=0)

So I get the y coordinate and just want to get the coordinate so I can draw a line from the x axis to the curve.

Ah ok, I understand now. The best is to write a function looping on all the bins and for each bin corresponding to the value you want, you draw the line.