Comment by theguitarman

Comment by theguitarman 2 days ago

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A concern I have for modern day mapping systems is that digital maps, like Google Maps and OpenStreetMap (OSM), typically operate on the assumption of a static, rigid Earth. I don’t know much about it, but from what I understand, they use coordinate systems like WGS84, which are a snapshot in time. These would be great for local precision but less so for tectonic precision, due to tectonic plate activity (continental drift), post-glacial rebound (areas still rising after ice sheets melted), and sudden seismic events (earthquakes).

And then there’s GPS coordinate shift. From what I read, ITRF, ETRS89, and coordinates associated with epoch dates attempt to deal with this.

So, even though it may not matter as much for FlightAware maps, autonomous and GPS-based systems are a little worrying. Being overly dependent on them may have some be risk over time.

marklit 2 days ago

I'm having a hard time tracking down the OSM-specific actions around this but Australia moved 1.8M back in 2017 due to continental shifting https://www.ga.gov.au/news/news-archive/australia-officially...

The Airport in Tartu, Estonia had a navigation upgrade last year in order to help mitigate navigation jamming that's taking place in the region. https://www.eans.ee/en/uudised/tanasest-saab-tartu-lennuvalj...

Defcon had a great talk on all the different navigational systems pilots can use and a note at the end that these shouldn't be decommissioned at the rate they're experiencing atm https://www.youtube.com/watch?v=wSVdfOn737o

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phoronixrly 2 days ago

OSM is a community of predominantly amateurs/enthusiasts who trace uncorrected satellite photos and store the data as WGS-84 coordinates with 7-digit 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... And OSM is plenty useful even without outstanding precision.

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  • hdgvhicv 2 days ago

    Whenever I’ve done things on OSM it’s based on gps recorded tracks - no doubt not particularly accurate but there are many overlaid ones which average out to be fairly precise (1mish) for the purpose.

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    • phoronixrly 2 days ago

      Oh yeah, I forgot about the enthusiasts that use uncorrected GPS positioning with low-cost hardware. One meter precision at the very best of conditions...

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  • 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.

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    • 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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jvvw 2 days ago

For a while I worked on a project related to mapping the ancient world (so you could e.g. click on a ancient city and then see items from museums from that city, references in ancient texts etc) and one of the interesting problems was not just that cities changed over time but that things like coastlines also did.

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  • efskap 2 days ago

    Sounds super compelling, did it end up launching?

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cyberax 2 days ago

This is a real problem for applications that need to deal with precise locations. For example, if you want to estimate the roof sizes using the aerial imagery and the LIDAR point clouds (e.g. the one from the USGS: https://usgs.entwine.io/data/view.html?r=%22https://s3-us-we... ).

The coordinates do not align precisely in many locations, exactly because of the actual motion of the Earth's surface. Tectonic plates, aquifer depletion, land sliding down the mountain slopes, etc. For practical applications, there are steps in the data processing to fit the different datasets together ("registering" one of them). As long as you have timestamped maps, you can reasonably reconstruct the current WGS84 coordinates by fitting the data together.

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  • defrost 2 days ago

    As geodetic problems go, though, this is trivial small beer stuff compared to, say, stitching together magnetic maps measured on different days or gathered in flight in different flight directions, or normalising continental scale radiometric datasets gathered across decades.

    Modern digital post WGS84 mapping is a breeze compared to the days of dealing with chains under tension and stitching together across differing ellipsoids and datums.

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