I figured I’d make a thread that would detail GPS accuracy for every tech tree in-game now that GPS bombs are here. Some GPS systems are more accurate for military purposes than other GPS systems. Perhaps that should be reflected in-game?
This place would serve as a collection of sources and discussions of whether or not GPS accuracy should be modeled based on military systems.
Italy: Galileo
France: Galileo
Germany: Galileo
Sweden: Galileo
UK: US
US: GPS
China: BeiDou
Russia: GLONASS
Japan Quasi-Zenith, enhancement of US’ GPS
Israel: GPS
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For the US’ GPS:
The Precise Positioning Service (PPS) is a highly accurate military positioning, velocity and timing service which will be available on a continuous, worldwide basis to users authorized by the U.S. P(Y) code capable military user equipment provides a predictable positioning accuracy of 2.7 meters (95 percent) horizontally and 4.9 meters vertically
Source: Global Positioning System Overview
Horizontally: 1.82m, Vertically: 4.52m
Source: SPS Performanace Analysis Report
Thanks to @TomLiu126
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For China’s BeiDou system:
Positioning accuracy: horizontally, 0.3 meters; vertically, 0.6 meters;
Source:
http://www.beidou.gov.cn/xt/gfxz/202105/P020210526216231136238.pdf.
Thanks to @TomLiu126
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For Galileo’s HAS system:
Positioning accuracy: <20cm horizontally, <40cm vertically
Source: Galileo High Accuracy Service (HAS) | European GNSS Service Centre (GSC)
GPS systems are already pretty accurate under ideal situations, so I doubt that there would be noticeable differences between them. More interesting would be introducing inaccuracies due to environmental factors (atmospheric effects, ground cover, multipathing, etc.), but I don’t know how hard that would be implement, or whether that would be desirable.
Some publicly available accuracy figures, though they may be measured under specific circumstances that might not be universially applicable:
GPS: 1.82 m (https://www.nstb.tc.faa.gov/reports/2020_Q4_SPS_PAN_v2.0.pdf#page=38, from 2020)
Galileo: 20 cm for High Accuracy Service (Galileo High Accuracy Service (HAS) | European GNSS Service Centre (GSC))
BeiDou: 10 cm (Precise orbit determination of Beidou Satellites with precise positioning, from 2012, allegedly military use only)
GLONASS: 1.32 m (Tough Times for Russian Navigation System - GPS World, unreliable source?)
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Ideally there would be primary sources for BeiDou and GLONASS.
In-game it could be the difference between a severe crit on a tank and outright destruction, especially for some of the smaller GPS bombs.
Don’t forget that we’re supposed to take into account both the horizontal and vertical positioning accuracy
Vertical error is on the previous page of the source, at 4.52 m.
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The SDB has a 26.45 kg TNT equivalent, which is pretty close to AN-M30 100 lb bomb (24.5 kg TNT equivalent). The “radius of destruction of armoured vehicles” for that is listed at 2 m in game. Problem is that due to a bug in game, bombs landing right on top of vehicles sometimes don’t overpressure it (not to mention that some tanks have ERA or composites on their turret roofs as well), so it would have to land within a 2 m band surrounding the target, which would require sub-1 metre accuracy. Right now our sources only definitively indicate that Galileo’s HAS has that level of accuracy.
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Implementing accurate GPS deviation depending on systems would definitely encourage users to use bigger bombs and not the smaller ones. Also, 1m might be the difference between the bomb landing on top of the target, or the building that he’s hugging, which would mean no effect on the target.
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Regarding Beidou, there’s a newer version of that standards document you used (version 3.0 from 2021) here: http://www.beidou.gov.cn/xt/gfxz/202105/P020210526216231136238.pdf. It states that the “accuracy standard” is 9 m horizontal and 10 m vertical.
However, the standard is generally a minimum guarantee, which would probably be more lenient than the actual average performance. In an official news release, the average accuracy is stated to be 2-3 m (2.34 m specifically), though regrettably they do not specify whether it’s horizontal or vertical.
Sources (all in Chinese, unfortunately):
http://www.beidou.gov.cn/yw/gjdt/202211/t20221123_25168.html
Image from source:
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The standard used for BeiDou is the same standard used for the primary sources of the other systems which is 95% positional accuracy.
Spoiler
That is true.
On the other hand though, I just noticed in the same standards document that there is a separate service called the Precise Point Positioning (PPP) Service (described from page 19 onwards). That one is still a satellite-only system (as opposed to the Ground Augmentation System (GAS) Service that uses mobile communication information) and can achieve 30 cm horizontal and 60 cm vertical accuracy using BDS alone (there’s a weird BDS+GPS system with even higher accuracy, akin to Galileo’s HAS, but I doubt that the US would be open to allowing GPS augmentation in a hypothetical war scenario).
Table from page 21:
Could you look into BDS more and tell me what it is? That seems to be interesting
Uhhh, BDS is just the acronym for BeiDou System, if that’s what you’re asking?
Fair enough, I’ll incorporate this new data. I thought perhaps BDS is a completely different system for China, but it is not.
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What’s left is Quasi-Zenith and Glonass so far
If I’m interpreting their documents correctly, Quasi-Zenith (QZSS) provides three main services: the basic Positioning, Navigation, and Time Service (PNT); the Sub-meter Level Augmentation Service (SLAS); and the Centimeter Level Augmentation Service (CLAS). Of these three, CLAS is stated to suffer from 10 to 20 seconds of lag and should be limited to specific areas (source: https://qzss.go.jp/en/overview/services/sv06_clas.html), so I doubt it would be used for military purposes. SLAS might be usable, but it’s still said to suffer from time lag, though somewhat less and can be used for pedestrians, bicycles, ships, etc (source: Sub-meter Level Augmentation Service (SLAS)｜Service Overview｜QZSS (Quasi-Zenith Satellite System) - Cabinet Office (Japan)). To be honest, I’m not sure if QZSS is actually used for military purposes, they might just use basic GPS.
According to status reports from 2024:
PNT has a Root Mean Square User Range Error ranging from 0.56 - 1.02 m, but that doesn’t translate directly into horizontal and vertical errors (source: https://sys.qzss.go.jp/serv_report/SPO/Service%20performance%20report_for_1stH_FY2024_PNT.pdf)
SLAS has horizontal accuracy ranging from 0.59 to 2.29 m, and vertical accuracy ranging from 0.76 to 2.70 m, just eyeballing the data table (source: https://sys.qzss.go.jp/serv_report/SLA/Service%20performance%20report_for_1stH_FY2024_SLAS.pdf)
The source for CLAS is here: https://sys.qzss.go.jp/serv_report/CLA/Service%20performance%20report_for_1stH_FY2024_CLAS.pdf. I’m not going to calculate the results since there are even more data points here, but just a cursory glance suggests that accuracy is within 10 cm.
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It’s been said that the Japanese military uses US’ GPS in addition to Quasi-Zenith to provide more accuracy, so the numbers should be greater than the US’ precisions.
Yeah, I think you’re right that QZSS is also used. This IISS article says that their naval ships started using QZSS in 2019 as a backup for GPS. The remaining question is which mode they use it in. If they just use PNT, the accuracy may be marginally higher due to the larger number of satellites available (which allows for better dilution of precision). SLAS might be used at some installations, but as the source shows, there can be some variability in accuracy, perhaps due to time lag.
It should also be noted that right now the only GNSS weapons in the Japanese air tree are on the Thai JAS39C, which probably just used normal GPS in real life (though QZSS is apparently interoperable with GPS, so it may benefit from the enhanced precision from the PNT mode). QZSS will become more relevant when the Mitsubishi F-2 arrives in-game.
