Comment by cyberax

Comment by cyberax 2 days ago

OSM uses a hundred nanodegrees as the grid resolution ( https://github.com/openstreetmap/OSM-binary/blob/32c3e921665... ). It gives a bit more than 1cm precision.

> The point I'm trying to make is that there are more important sources of error before you get to tectonic movement and GPS drift...

You can absolutely measure tectonic drift on the OSM maps! They've existed long enough for it to be actually significant in a lot of places if you download the old data.

This also comes up all the time when trying to overlap data from local agencies onto the OSM maps. You end up with parcel boundaries visibly off.

phoronixrly 2 days ago

> OSM uses a hundred nanodegrees as the grid resolution

As I said, 7-digit precision.

> You can absolutely measure tectonic drift on the OSM maps! They've existed long enough for it to be actually significant in a lot of places if you download the old data. > > This also comes up all the time when trying to overlap data from local agencies onto the OSM maps. You end up with parcel boundaries visibly off.

Yeah, assuming the person who added the features you're observing as 'visibly off' did not use 1-meter Bing imagery with a 10-meter offset...

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ericpauley 2 days ago

This is not the correct way to count digit precision, which should be independent of the units used. If there were 360,000 degrees in a circle would this same precision suddenly be 4 digits? If we measured in radians would the digit precision become 9? Of course not…
Given the 100ndeg precision is across the full earth, this would be 1 part per 3.6 billion or 9.5ish digits of precision. The location of the decimal point when displaying it is irrelevant.

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- willtemperley 2 days ago
  
  What also needs to be taken into account is that real world longitudinal distance changes by the cosine of latitude. 1 degree of longitude is 111km at the equator and 19km at 80 degrees.
  In GIS the gold standard for positional accuracy is the Root Mean Square Error, measured in real world distance units.
  
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cyberax 7 hours ago

> As I said, 7-digit precision.
9 digits, because there are 2.5 digits of precision in 0-360 degrees left of the decimal point.

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