Hi!
If you share your SilverStone_Coords.txt I can have a look.
However, you might have more luck converting to UTM instead of ECEF, I find ECEF pretty awkward to work with.
Ordnance survey have info on algorithms:
https://www.ordnancesurvey.co.uk/documents/resources/guide-coordinate-systems-great-britain.pdf (Appendix C)
You could maybe batch-convert your file to National Grid:
National Grid should be good for Silverstone, probably no good for stuff outside the UK, I’m not sure.
I bet there is a C# Lat,lon > UTM thing somewhere and/or a batch conversion program (I thiink NovAtel have one), but I thought I’d best link stuff I was familiar with.
I don’t think it’ll be causing your problem, but I think I’d use double-precision everywhere, at least until you get as far as the final output points. Using double-precision for the dataset, then applying some offset to make the co-ordinates relative to the start point, and then switching to floats is maybe nicest. I think UTM runs out of precision otherwise.
Code’s easier to read if you use code tags, info here: