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The trouble is, the documentation is just wrong - all the official documentation says that OSM is in WGS-84. When I realised that this couldn't actually work du

by makomk 7y ago

The trouble is, the documentation is just wrong - all the official documentation says that OSM is in WGS-84. When I realised that this couldn't actually work due to plate tectonics and tried to figure out what they were actually doing, all I found was an April fool's joke from a couple of years ago: https://blog.openstreetmap.org/2017/03/31/osm-plate-tectonics/ https://blog.openstreetmap.org/2017/03/31/osm-plate-tectonic...

not2b 7y ago
I've contributed to OSM, fixing trail maps based on traces I recorded with my Garmin GPSMAP 64 which is configured to use WGS-84. If OSM wants something else they'd better let their contributors know how to deal with this.
- makomk 7y ago
  It doesn't matter too much when using normal GPS receivers for mapping because the difference between datums is less than the position error. The main reason I was looking into it is because I was experimenting with a GPS setup that could theoretically achieve high enough accuracy for this to matter.
maxerickson 7y ago
Interpreting OSM as if it mattered would anyway be a mistake. The data does not have consistent or reliable accuracy and precision. Edit: Someone has downvoted this. It's an important point to remember when using OSM. Many GIS datasets are developed in a way that the accuracy and precision of the data is consistent across the entire dataset. OSM doesn't bother with this, because it's really hard to do, especially globally. That doesn't make OSM less useful for making consumer maps (there's no problem if data is off by 2 or 4 meters or whatever), but it can be a problem if say you were trying to make a legal determination about property ownership. OSM isn't a useful source for the latter task and would have to fundamentally change to become so.
- mikekchar 7y ago
  To back this up, when I was making maps of the rural area where I live in Japan, there were a few places where aerial maps were obscured by trees and where GPS measurements were wildly inaccurate due to geographical features. So I just guessed where the road was. It's in there somewhere and if you are driving your car or riding your bike, it's more than good enough. If you needed to know the precise location of that road for another purpose? Totally useless. Maybe someone has gone in and improved my initial efforts, maybe not (although, I was looking at it the other day and I'm pretty sure they have).

by makomk 7y ago

not2b 7y ago

I've contributed to OSM, fixing trail maps based on traces I recorded with my Garmin GPSMAP 64 which is configured to use WGS-84. If OSM wants something else they'd better let their contributors know how to deal with this.

makomk 7y ago
It doesn't matter too much when using normal GPS receivers for mapping because the difference between datums is less than the position error. The main reason I was looking into it is because I was experimenting with a GPS setup that could theoretically achieve high enough accuracy for this to matter.

maxerickson 7y ago

Interpreting OSM as if it mattered would anyway be a mistake. The data does not have consistent or reliable accuracy and precision. Edit: Someone has downvoted this. It's an important point to remember when using OSM. Many GIS datasets are developed in a way that the accuracy and precision of the data is consistent across the entire dataset. OSM doesn't bother with this, because it's really hard to do, especially globally. That doesn't make OSM less useful for making consumer maps (there's no problem if data is off by 2 or 4 meters or whatever), but it can be a problem if say you were trying to make a legal determination about property ownership. OSM isn't a useful source for the latter task and would have to fundamentally change to become so.

mikekchar 7y ago
To back this up, when I was making maps of the rural area where I live in Japan, there were a few places where aerial maps were obscured by trees and where GPS measurements were wildly inaccurate due to geographical features. So I just guessed where the road was. It's in there somewhere and if you are driving your car or riding your bike, it's more than good enough. If you needed to know the precise location of that road for another purpose? Totally useless. Maybe someone has gone in and improved my initial efforts, maybe not (although, I was looking at it the other day and I'm pretty sure they have).