4 ms·

Nothing in this article is new, and the problem with RTK has always been the (unpaid) availability of reference stations. Good on them for trying to make a pack

Nothing in this article is new, and the problem with RTK has always been the (unpaid) availability of reference stations. Good on them for trying to make a package of it, but maybe this "news" site could've used a bit less unchecked enthusiasm. Also, RTK is the opposite of "regular" GPS, it's generally considered a "special" usage mode of GPS. And discussing urban canyons with no mention of QZSS?

tecleandor 1y ago
Fun thing (?), I was excited on my last trip to Japan so I could test QZSS with my Pixel 9a, that supports it, and my GPS experience in urban canyons, specially in Shibuya, was terribly bad. Even when in GPS Test or GPS Lock tools it was showing better than 3 meter horizontal accuracy, and a multitude of locked satellites, including some QZSS, the location would usually be 30 to 50 meters away. The first days I though I had lost all my capacity to navigate Tokyo, then I noticed the GPS was gas-lightning me. I tried removing the phone case, changing GPS settings... and I had no luck.
- jlack 1y ago
  Extra satellites only have the potential to help a little bit in urban environments by increasing the odds of having a satellite directly overhead. Dense urban environments will have high multipath(longer time for signal to get to the receiver due to bouncing off buildings) which causes the position to be inaccurate.
  - cyanydeez 1y ago
    They hand waved over a lot of it. The improvements in the urban canyon are not coming from GPS, but from things like wifi and 3d mapping, probably including cellular triangulations.
leecb 1y ago
> The Quasi-Zenith Satellite System (QZSS) (Japanese: 準天頂衛星システム, Hepburn: juntenchō eisei shisutemu), also known as Michibiki (みちびき, "guidance"), is a regional navigation satellite system (RNSS) and a satellite-based augmentation system (SBAS) developed by the Japanese government to enhance the United States-operated Global Positioning System (GPS) in the Asia-Oceania regions, with a focus on Japan. https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System
sampton 1y ago
Using building geometry to correct gnss signals is new.
- addaon 1y ago
  I recall Uber looking into this around 8 years ago? Don’t know if it went past a publication.
  - ingsoc79 1y ago
    Yep, they also used 3D building data for correcting position in urban canyons: https://www.uber.com/blog/rethinking-gps/ https://www.uber.com/blog/rethinking-gps/
mapt 1y ago
Can we agree that with close to 10,000 Starlink birds in the air and counting, that whatever succeeds GPS needs to be a much larger constellation than the 30-unit GPS constellation in MEO, flying much lower? It is absolutely insane to me that Japan would be trying to economize using Molniya orbits or geosynchronous orbits in 2025. Some BOTE math: There are ~40k square degrees in a sphere. If I'm in a dead-end alley in an urban canyon and I have access to a 40 degree by 100 degree viewshed of sky (~4000 square degrees), that's 10% of the sky. Surface area of a 900km sphere is ~10 million square kilometers, 10% of that is 1 million square kilometers, Earth's radius is ~6400km, the orbital radius at 1000km is ~7400km, surface area of a 7400km radius sphere is ~700 million square kilometers, 1 million / 700 million ~= 1/700. Fly 3500 birds and you'll on average see five of them at a time in a 40 by 100 degree viewshed. But you'll have such a large angular parallax between their positions, and so little of the ionosphere in the way, that you get extremely high accuracy. ... Many countries have their own SBAS to correct for ionospheric ephemera using a combination of regional ground stations and low flying satellites - The US calls their WAAS, Europe uses EGNOS, Japan uses MSAS, Russia and China have versions for their respective constellations, etc. QZSS is a related but distinct idea that poses a little more like a localized addition to the GPS constellation.
- sorenjan 1y ago
  There are efforts on building LEO PNT (Low Earth Orbit Position Navigation Timing) constellations. I just really really hope it wont be a private company like SpaceX that operates it, having GPS and later the other GNSS constellations available for free have been essential for a lot of use cases. https://www.esa.int/Applications/Satellite_navigation/LEO-PNT https://www.esa.int/Applications/Satellite_navigation/LEO-PN... https://www.thalesgroup.com/en/solutions-catalogue/leo-pnt https://www.thalesgroup.com/en/solutions-catalogue/leo-pnt https://www.xonaspace.com/ https://www.xonaspace.com/
- eqvinox 1y ago
  > Can we agree that with close to 10,000 Starlink birds in the air and counting, that whatever succeeds GPS needs to be a much larger constellation than the 30-unit GPS constellation in MEO, flying much lower? For the record, block III GPS satellites are 3880kg. A Starlink satellite is 800kg. But I don't know how much of the GPS satellites' weight is a necessity due to the atomic clocks they carry. Either way the constellation would be at least a bit smaller due to launch costs.
cyanydeez 1y ago
It ready mostly like an advertisement for Google's API.

tecleandor 1y ago

Fun thing (?), I was excited on my last trip to Japan so I could test QZSS with my Pixel 9a, that supports it, and my GPS experience in urban canyons, specially in Shibuya, was terribly bad. Even when in GPS Test or GPS Lock tools it was showing better than 3 meter horizontal accuracy, and a multitude of locked satellites, including some QZSS, the location would usually be 30 to 50 meters away. The first days I though I had lost all my capacity to navigate Tokyo, then I noticed the GPS was gas-lightning me. I tried removing the phone case, changing GPS settings... and I had no luck.

jlack 1y ago
Extra satellites only have the potential to help a little bit in urban environments by increasing the odds of having a satellite directly overhead. Dense urban environments will have high multipath(longer time for signal to get to the receiver due to bouncing off buildings) which causes the position to be inaccurate.
- cyanydeez 1y ago
  They hand waved over a lot of it. The improvements in the urban canyon are not coming from GPS, but from things like wifi and 3d mapping, probably including cellular triangulations.

leecb 1y ago

> The Quasi-Zenith Satellite System (QZSS) (Japanese: 準天頂衛星システム, Hepburn: juntenchō eisei shisutemu), also known as Michibiki (みちびき, "guidance"), is a regional navigation satellite system (RNSS) and a satellite-based augmentation system (SBAS) developed by the Japanese government to enhance the United States-operated Global Positioning System (GPS) in the Asia-Oceania regions, with a focus on Japan. https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System https://en.wikipedia.org/wiki/Quasi-Zenith_Satellite_System

sampton 1y ago

Using building geometry to correct gnss signals is new.

addaon 1y ago
I recall Uber looking into this around 8 years ago? Don’t know if it went past a publication.
- ingsoc79 1y ago
  Yep, they also used 3D building data for correcting position in urban canyons: https://www.uber.com/blog/rethinking-gps/ https://www.uber.com/blog/rethinking-gps/

mapt 1y ago

Can we agree that with close to 10,000 Starlink birds in the air and counting, that whatever succeeds GPS needs to be a much larger constellation than the 30-unit GPS constellation in MEO, flying much lower? It is absolutely insane to me that Japan would be trying to economize using Molniya orbits or geosynchronous orbits in 2025. Some BOTE math: There are ~40k square degrees in a sphere. If I'm in a dead-end alley in an urban canyon and I have access to a 40 degree by 100 degree viewshed of sky (~4000 square degrees), that's 10% of the sky. Surface area of a 900km sphere is ~10 million square kilometers, 10% of that is 1 million square kilometers, Earth's radius is ~6400km, the orbital radius at 1000km is ~7400km, surface area of a 7400km radius sphere is ~700 million square kilometers, 1 million / 700 million ~= 1/700. Fly 3500 birds and you'll on average see five of them at a time in a 40 by 100 degree viewshed. But you'll have such a large angular parallax between their positions, and so little of the ionosphere in the way, that you get extremely high accuracy. ... Many countries have their own SBAS to correct for ionospheric ephemera using a combination of regional ground stations and low flying satellites - The US calls their WAAS, Europe uses EGNOS, Japan uses MSAS, Russia and China have versions for their respective constellations, etc. QZSS is a related but distinct idea that poses a little more like a localized addition to the GPS constellation.

sorenjan 1y ago
There are efforts on building LEO PNT (Low Earth Orbit Position Navigation Timing) constellations. I just really really hope it wont be a private company like SpaceX that operates it, having GPS and later the other GNSS constellations available for free have been essential for a lot of use cases. https://www.esa.int/Applications/Satellite_navigation/LEO-PNT https://www.esa.int/Applications/Satellite_navigation/LEO-PN... https://www.thalesgroup.com/en/solutions-catalogue/leo-pnt https://www.thalesgroup.com/en/solutions-catalogue/leo-pnt https://www.xonaspace.com/ https://www.xonaspace.com/
eqvinox 1y ago
> Can we agree that with close to 10,000 Starlink birds in the air and counting, that whatever succeeds GPS needs to be a much larger constellation than the 30-unit GPS constellation in MEO, flying much lower? For the record, block III GPS satellites are 3880kg. A Starlink satellite is 800kg. But I don't know how much of the GPS satellites' weight is a necessity due to the atomic clocks they carry. Either way the constellation would be at least a bit smaller due to launch costs.

cyanydeez 1y ago

It ready mostly like an advertisement for Google's API.