Hi, this is not 100% GPS but Google points me here again and again. I want to calculate the Vertical and Horizontal Dilution of Precision (more concretely for multilateration instead of GPS but this should be just the same?). Essentially, the gif from Wikipedia (cf. attachement EDIT: It's to small and I'm not allowed to put a link, but it's the example from Wikipedia, linked in the references) is perfectly understandable for GDOP, PDOP, TDOP with 5 points in ECEF. But how to find VDOP and HDOP on the earth surface? Taking the sqrt of Dx1 or sqrt(Dx1 + Dy2) doesn't work if I'm not mistaken. It also looks weird when plotted. The same site now suggests "ECEF XYZ DOP terms can be rotated into a North-East Down (NED) system to produce local horizontal and vertical DOP terms". It's simple to look up how to convert in NED but I don't really see at what point to do that to get those terms? Any help/resource very appreciated! Thanks
