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Except this doesn’t work on smartphones. Have you ever tried using GPS? It doesn’t understand what direction you’re facing unless you’re steadily moving forward

Except this doesn’t work on smartphones. Have you ever tried using GPS? It doesn’t understand what direction you’re facing unless you’re steadily moving forward.

scotty79 10mo ago
It's because maps apps don't trust builtin compass. Which is reasonable since it fairly often loses calibration.
estimator7292 10mo ago
That's because GPS is not directional. It's a positioning system. Direction can only be inferred as the difference between locations. GPS fundamentally has no way of determining your direction. It was never designed for anything other than giving you a single fixed 3D location on the Earth's surface.
- robocat 10mo ago
  Rubbish: from first principles it is obvious that direction can be calculated. You are correct for phones, which have omnidirectional antennas that can't calculate direction (also built up areas with multipath would make direction finding difficult). Marine navigation systems are the most familiar example. Many boat GPS units advertise “GPS compass” or “true heading at zero speed.” . The antennas contain two GNSS elements, fixed a known distance apart, and the direction is found using phase comparison: they look at the tiny difference in arrival time of the same satellite signal at the two separate antennas. Either (a) don't answer if you don't know what you are talking about or better (b) double check your "facts" (using Google or AI) before answering.
  - scotty79 9mo ago
    You just basically confirmed what the previous commenter said. GPS is not directional. You need two of them placed some significant distance apart (think ship length, not smartphone length). When you have two points determined with high enough precision you obviously have a direction and even orientation. Your comment could have been just that. Useful information many people could find interesting. Instead you decided to sprinkle it with bile.
    - robocat 9mo ago
      You are doubling down - I do find your misinformation to be interesting. Have a look at images of the antennas: https://duckduckgo.com/?q=%22GPS+compass%22+antenna&ia=images&iax=images https://duckduckgo.com/?q=%22GPS+compass%22+antenna&ia=image... I do apologize for liking brutal facts - I am an engineer type. I clicked the Furuno antenna since it looked sexy - blurb: SC-130 features a Tri-sensor antenna that provides a high system accuracy for the heading of your vessel [for Autopilot, berthing etcetera.]. 0.25°rms Fist principles: I think wavelength of L1 GPS frequency is about 0.2m - the same order as smartphone length. A ship length baseline using phase would need precise engineering and would not work for satellites absolutely perpendicular to the ship (making it less ideal). Calculating phase difference only needs a single satellite visible, so I would guess directionality can be precise in built up areas even where location is harder to fix. although I'm assuming multipath can be filtered out.
      - scotty79 9mo ago
        SC-130 has distance between the antennas on the order of 1 meter and has three of them (which probably let's them be closer than in two antenna unit). If you test phase shift to one satelite you might get good accurancy for some directions and no accurancy at all for the orthogonal directions. So maybe not ship-length but still 1 meter sized device is way too large to put under the hood of a car let wlon in a smartphone. Again, GPS has no provisions for orientation detection. You can hack it with few antennas significantly spaced apart (thank you again for pointing out those solutions). I think it might be easier to detect location with GPS and orientation by testing phase shift to the closest cell tower (when on land). There's nothing in GPS system thst helps with determining orientation. And you still can't drop arrogance which gets tiresome.
        robocat 9mo ago
        Yes, I was being rude, but the OP and you are and choosing to write incorrect information. You in particular are redoubling your errors and arrogantly stating incorrect "facts". Here's a dual antenna direction finder smaller than a cellphone: Vectornav VN-310 embedded. Size: 31 x 31 x 11 mm. Power:<1.6W Weight: <15g. https://insideunmannedsystems.com/new-tactical-grade-dual-antenna-gnss-ins-shows-off-at-intergeo-and-ausa/ https://insideunmannedsystems.com/new-tactical-grade-dual-an... I had chosen the 1m Furuno because it was pretty, not because it was a great example. I personally suspect that the people that designed the GPS system deeply cared about using the system to calculate heading information for missiles and fighters. Unfortunately it is hard to get good information about either the system design or missile antennas. I did a quick search for information about missile antennas and learnt some stuff but I didn't find anything juicy. Some early and experimental GPS compasses used a rotating directional antenna. The idea was to use a patch or helix antenna that has a gain pattern. Spin it, watch signal strength from satellites rise and fall, and infer orientation. A few marine and military prototypes in the 1990s did this. Once dual-antenna phase comparison became practical, that approach died. An Android App could combine body-blocking direction finding (also called human-body RF shadowing) with GPS satellite strength metering to create a crude GPS based direction finder. If you designed an RF shade on a rotating axis, it wouldn't be that difficult to get a mobile phone to accurately detect true direction from the satellite ephemeris data. A lovely hacking project. Would be more fun with a highly directional antenna and pointing in 3D to any part of the sky. Disclosure: I'm no expert on any of this. I just like hacking.

Except this doesn’t work on smartphones. Have you ever tried using GPS? It doesn’t understand what direction you’re facing unless you’re steadily moving forward.

scotty79 10mo ago

It's because maps apps don't trust builtin compass. Which is reasonable since it fairly often loses calibration.

estimator7292 10mo ago

That's because GPS is not directional. It's a positioning system. Direction can only be inferred as the difference between locations. GPS fundamentally has no way of determining your direction. It was never designed for anything other than giving you a single fixed 3D location on the Earth's surface.

robocat 10mo ago
Rubbish: from first principles it is obvious that direction can be calculated. You are correct for phones, which have omnidirectional antennas that can't calculate direction (also built up areas with multipath would make direction finding difficult). Marine navigation systems are the most familiar example. Many boat GPS units advertise “GPS compass” or “true heading at zero speed.” . The antennas contain two GNSS elements, fixed a known distance apart, and the direction is found using phase comparison: they look at the tiny difference in arrival time of the same satellite signal at the two separate antennas. Either (a) don't answer if you don't know what you are talking about or better (b) double check your "facts" (using Google or AI) before answering.
- scotty79 9mo ago
  You just basically confirmed what the previous commenter said. GPS is not directional. You need two of them placed some significant distance apart (think ship length, not smartphone length). When you have two points determined with high enough precision you obviously have a direction and even orientation. Your comment could have been just that. Useful information many people could find interesting. Instead you decided to sprinkle it with bile.
  - robocat 9mo ago
    You are doubling down - I do find your misinformation to be interesting. Have a look at images of the antennas: https://duckduckgo.com/?q=%22GPS+compass%22+antenna&ia=images&iax=images https://duckduckgo.com/?q=%22GPS+compass%22+antenna&ia=image... I do apologize for liking brutal facts - I am an engineer type. I clicked the Furuno antenna since it looked sexy - blurb: SC-130 features a Tri-sensor antenna that provides a high system accuracy for the heading of your vessel [for Autopilot, berthing etcetera.]. 0.25°rms Fist principles: I think wavelength of L1 GPS frequency is about 0.2m - the same order as smartphone length. A ship length baseline using phase would need precise engineering and would not work for satellites absolutely perpendicular to the ship (making it less ideal). Calculating phase difference only needs a single satellite visible, so I would guess directionality can be precise in built up areas even where location is harder to fix. although I'm assuming multipath can be filtered out.
    - scotty79 9mo ago
      SC-130 has distance between the antennas on the order of 1 meter and has three of them (which probably let's them be closer than in two antenna unit). If you test phase shift to one satelite you might get good accurancy for some directions and no accurancy at all for the orthogonal directions. So maybe not ship-length but still 1 meter sized device is way too large to put under the hood of a car let wlon in a smartphone. Again, GPS has no provisions for orientation detection. You can hack it with few antennas significantly spaced apart (thank you again for pointing out those solutions). I think it might be easier to detect location with GPS and orientation by testing phase shift to the closest cell tower (when on land). There's nothing in GPS system thst helps with determining orientation. And you still can't drop arrogance which gets tiresome.
      - robocat 9mo ago
        Yes, I was being rude, but the OP and you are and choosing to write incorrect information. You in particular are redoubling your errors and arrogantly stating incorrect "facts". Here's a dual antenna direction finder smaller than a cellphone: Vectornav VN-310 embedded. Size: 31 x 31 x 11 mm. Power:<1.6W Weight: <15g. https://insideunmannedsystems.com/new-tactical-grade-dual-antenna-gnss-ins-shows-off-at-intergeo-and-ausa/ https://insideunmannedsystems.com/new-tactical-grade-dual-an... I had chosen the 1m Furuno because it was pretty, not because it was a great example. I personally suspect that the people that designed the GPS system deeply cared about using the system to calculate heading information for missiles and fighters. Unfortunately it is hard to get good information about either the system design or missile antennas. I did a quick search for information about missile antennas and learnt some stuff but I didn't find anything juicy. Some early and experimental GPS compasses used a rotating directional antenna. The idea was to use a patch or helix antenna that has a gain pattern. Spin it, watch signal strength from satellites rise and fall, and infer orientation. A few marine and military prototypes in the 1990s did this. Once dual-antenna phase comparison became practical, that approach died. An Android App could combine body-blocking direction finding (also called human-body RF shadowing) with GPS satellite strength metering to create a crude GPS based direction finder. If you designed an RF shade on a rotating axis, it wouldn't be that difficult to get a mobile phone to accurately detect true direction from the satellite ephemeris data. A lovely hacking project. Would be more fun with a highly directional antenna and pointing in 3D to any part of the sky. Disclosure: I'm no expert on any of this. I just like hacking.