3 ms·

That's not as accurate as you think unless you've got a full geodetic antenna. (i.e. $200k worth of equipment + a lot of permits to be allowed to have/use it)

by jofer 7y ago

That's not as accurate as you think unless you've got a full geodetic antenna. (i.e. $200k worth of equipment + a lot of permits to be allowed to have/use it) Getting to within +/- 30m doesn't help a ton when you're digging a hole to find a small box. With geocaching, you've got something to look for. You get close-ish and then do an easter egg hunt. When it's beneath the ground, it's really hard to "look". Finding easter eggs with a shovel ain't my cup of tea.

saalweachter 7y ago
Doesn't modern GPS claim +/- 3 meters, with a clear enough signal? (Which is still a heckuva lot of dirt to shift.)
- jofer 7y ago
  Given nearby local ground-based correction stations (e.g. WAAS) it can use and flat terrain, yeah, you can certainly get that kind of accuracy. In practice, though, I've spent a fair bit of time trying to re-occupy sites taken with handheld GPS receivers. (I'm a geologist -- it comes up a lot) 30m is a better representation of typical repeatability for a consumer-grade handheld unit or a phone. You're often on the side of a hill, so you can't see the full constellation. If you don't have line-of-sight to more than a few satellites, you risk an inaccurate location. You're often in highly remote areas, so WAAS doesn't always help (it's based on proximity to a ground station). If you don't have WAAS, you're at the risk of atmospheric effects significantly affecting your accuracy. There's also the user error side: You might have the handheld set to display in NAD27 one time and WGS84 another, which can easily offset the same lat/long by several hundred meters. +/- 3m with consumer GPS is definitely possible, but that's for ideal conditions. You're rarely working with ideal conditions in the field.
  - grawprog 7y ago
    The best i've ever personally got with a handheld GPS under actual work conditions was +/- 15m. I've gotten +/- 5m in large open areas lacking trees, mountains or large rock formations but areas without any of those things are rare. Weather conditions can make a big difference. In stormy or rainy weather I was lucky if I could get +/-20m
- im3w1l 7y ago
  When you narrowed it down that much you might be able to use a metal detector or similar.
CamperBob2 7y ago
An extreme exaggeration. Geodetic antennas are neither regulated nor necessary. Any decent GPS receiver -- meaning less than US $100 -- will get you to within a couple of meters, even without WAAS. Of course, in a SHTF scenario, GPS accuracy will start to degrade fairly rapidly as soon as the control stations are gone. So your point about not being able to return to the same spot is certainly valid.
ChrisLomont 7y ago
Real-time Kinematic GPS (RTK-GPS) [1], available from Sparkfun for $200 [2] (and cheaper elsewhere), gets you centimeter accurate positioning in the US and most other countries. [1] https://en.wikipedia.org/wiki/Real-time_kinematic https://en.wikipedia.org/wiki/Real-time_kinematic [2] https://learn.sparkfun.com/tutorials/what-is-gps-rtk/all https://learn.sparkfun.com/tutorials/what-is-gps-rtk/all

by jofer 7y ago

saalweachter 7y ago

Doesn't modern GPS claim +/- 3 meters, with a clear enough signal? (Which is still a heckuva lot of dirt to shift.)

jofer 7y ago
Given nearby local ground-based correction stations (e.g. WAAS) it can use and flat terrain, yeah, you can certainly get that kind of accuracy. In practice, though, I've spent a fair bit of time trying to re-occupy sites taken with handheld GPS receivers. (I'm a geologist -- it comes up a lot) 30m is a better representation of typical repeatability for a consumer-grade handheld unit or a phone. You're often on the side of a hill, so you can't see the full constellation. If you don't have line-of-sight to more than a few satellites, you risk an inaccurate location. You're often in highly remote areas, so WAAS doesn't always help (it's based on proximity to a ground station). If you don't have WAAS, you're at the risk of atmospheric effects significantly affecting your accuracy. There's also the user error side: You might have the handheld set to display in NAD27 one time and WGS84 another, which can easily offset the same lat/long by several hundred meters. +/- 3m with consumer GPS is definitely possible, but that's for ideal conditions. You're rarely working with ideal conditions in the field.
- grawprog 7y ago
  The best i've ever personally got with a handheld GPS under actual work conditions was +/- 15m. I've gotten +/- 5m in large open areas lacking trees, mountains or large rock formations but areas without any of those things are rare. Weather conditions can make a big difference. In stormy or rainy weather I was lucky if I could get +/-20m
im3w1l 7y ago
When you narrowed it down that much you might be able to use a metal detector or similar.

CamperBob2 7y ago

An extreme exaggeration. Geodetic antennas are neither regulated nor necessary. Any decent GPS receiver -- meaning less than US $100 -- will get you to within a couple of meters, even without WAAS. Of course, in a SHTF scenario, GPS accuracy will start to degrade fairly rapidly as soon as the control stations are gone. So your point about not being able to return to the same spot is certainly valid.

ChrisLomont 7y ago

Real-time Kinematic GPS (RTK-GPS) [1], available from Sparkfun for $200 [2] (and cheaper elsewhere), gets you centimeter accurate positioning in the US and most other countries. [1] https://en.wikipedia.org/wiki/Real-time_kinematic https://en.wikipedia.org/wiki/Real-time_kinematic [2] https://learn.sparkfun.com/tutorials/what-is-gps-rtk/all https://learn.sparkfun.com/tutorials/what-is-gps-rtk/all