Sub-inch Accuracy GPS or Alternatives

[Builder1]

Hi all,
Does anyone know if there is such a thing as a cheap gps that is accurate down to below an inch? If such a thing is not available are there alternatives? Any help will be greatly appreciated, thanks.

Builder1

[knossos]

You won't get sub-inch accuracy from GPS.  Are you sure you even need that kind of accuracy?  Given more information we could probably point you in a better direction.

[madsci1016]

Hi all,
Does anyone know if there is such a thing as a cheap gps that is accurate down to below an inch? If such a thing is not available are there alternatives? Any help will be greatly appreciated, thanks.

Builder1

Yeah, but not cheap. We have GPS's at work that get this good, but they cost $3000 a piece and you need two of them (one as a base station) and radio gear so they can talk to each other.

Knossos is right, tell us what you are doing so we can give suggestions, because GPS isn't what you are looking for.

[knossos]

Yeah, but not cheap. We have GPS's at work that get this good, but they cost $3000 a piece and you need two of them (one as a base station) and radio gear so they can talk to each other.

Yeah, but unless I'm mistaken, you are referring to milspec gear which, unless they have opened it up recently isn't available commercially.

[madsci1016]

Yeah, but unless I'm mistaken, you are referring to milspec gear which, unless they have opened it up recently isn't available commercially.

There is milspec, but there's also tech that let's you create your own differential signal. I was referring to RTK (Real Time Kinematic) systems.

This allows the units to calculate their relative position to millimeters, although their absolute position is accurate only to the same accuracy as the position of the base station. The typical nominal accuracy for these dual-frequency systems is 1 centimetre ± 2 parts-per-million (ppm) horizontally and 2 centimetres ± 2 ppm vertically.

[knossos]

Hmm, didn't realize they had gotten RTK that precise.  Never followed it much being stuck in a world of milspec.