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Comment by ivanhoe | Hacker News Reader

Does anyone here know what's the actual precision that we can get by the available equipment?

Survey-grade GPS (using CORS and WAAS correction) using RTK will give you accuracy to ~10 cm within a few seconds. You can get that down to several millimetres if you can tolerate post-processing several hours worth of static data.

Is accuracy at that level actually possible with GPS? Precision seems likely, but it is substantially more difficult to provide absolute accuracy at that level.

I'm by no means an expert, but yes, if you can use a modern realisation (e.g. ITRF2014) and have access to VLBI / DORIS / GNSS then sub-centimetre accuracy is possible, though not in real time.

Yes, but not on its own, that I am aware. High accuracy GPS is is based on a combination of GPS satellite data itself with real time or post-processed positional correction using references stations which themselves are placed in a known surveyed location.

In the US, 60 cm accuracy is often possible with nothing more than WAAS corrections. 10 or even 1 cm accuracy is often possible in real time with access to an RTK network.

It's true. But survey-grade coordinates generally are used in a universal transverse Mercator, or in some locales a Lambert conic or some other locally useful projection. Those projections take into account such things as the deviation of the earth's shape from a perfect sphere.

Rule about lat/long precision: If somebody says the words "datum" or "projection" to you, and you say "huh?", then you only need four digits after the decimal point in your lat/long coordinates. On the other hand, if you're designing an outdoor parking lot and you don't want puddles, please use survey-grade coordinates.

Depends on the equipment. Sub centimeter with the right equipment and appropriate reference station. 3 meters, typically, with consumer equipment.

I know what I can get on a Nexus 6P and it is not a pleasant number. To make things worse the logic calculating the accuracy is also broken (e.g. a GPS point stating 5m accuracy may jump around by tens of meters). tl;dr cheap phone gps are not to be trusted without a lot of vetting

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