GPS: 'the good, bad & ugly' article

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GPS: 'the good, bad & ugly' article

Postby Tortoise » Mon 19 Oct, 2020 7:06 am

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Re: GPS: 'the good, bad & ugly' article

Postby Warin » Mon 19 Oct, 2020 7:58 am

An error....
Quote "GPS satellites are also equipped to detect nuclear bomb detonations and relay Personal Locator Beacon (PLB) rescue messages."

Bull. I don't think GPS satellites carry the COSPAS system. Nor do COSPAS satellites carry the GPS system.

https://www.amsa.gov.au/safety-navigati ... ite-system

Having found that error I have not read further ... as there maybe more less obvious errors. And it is not dated 1st of April so...
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Re: GPS: 'the good, bad & ugly' article

Postby CraigVIC » Mon 19 Oct, 2020 9:48 am

I'd be interested to hear from anyone who has gotten lost due to a gps and how it happened.

I just use a phone and think the problems can be overstated. Certainly the accuracy is reduced in a gully or beneath a rock face but in that case the natural feature itself takes over navigation.
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Re: GPS: 'the good, bad & ugly' article

Postby wildwanderer » Mon 19 Oct, 2020 4:21 pm

I can see it happening but only in a very limited set of circumstances and only if a person kept plunging blindly forward.

For example

If you're in a thickly forested region and there is a false ridge and the true ridge both parallel and next to each other.

The GPS puts you on the wrong ridge(easy to happen) and you walk down that ridge leading to a spur taking you into a deep, forested and cliff lined labyrinth. If you bashed in there a bit it could be a struggle to find a way back up especially as the GPS accuracy would be impacted by the narrowness of the gullies.
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Re: GPS: 'the good, bad & ugly' article

Postby tom_brennan » Mon 19 Oct, 2020 9:51 pm

CraigVIC wrote:I'd be interested to hear from anyone who has gotten lost due to a gps and how it happened.

I just use a phone and think the problems can be overstated. Certainly the accuracy is reduced in a gully or beneath a rock face but in that case the natural feature itself takes over navigation.


A GPS/phone will be fine most of the time - however, you do still need to use navigational common sense when following the GPS.

If you're under a cliffline, you can still be out by hundreds of metres, though errors like that are probably less frequent now than 15-20 years ago. Hopefully the error doesn't last long and you don't spend too long wandering in the wrong direction. Similar if you're in a deep gully and having to pick which branch to go up, if there are a number of forks.

My long-standing preference is just to use the paper map, and use the GPS to check, if I need a second opinion. For easier on-track walks these days I will sometimes just use a GPS or phone, assuming I think there is little that can go wrong navigationally.
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Re: GPS: 'the good, bad & ugly' article

Postby CraigVIC » Tue 20 Oct, 2020 4:57 am

Like anything I think a gps takes a bit of practice and some awareness of whether what you are seeing in front of you is what you were expecting and if not why not.

I'm not concerned by most of the problems flagged in the article. I think the number one problem by a long, long margin is dropping the gps in a crevice or deep water and then needing to get out on map skills that are out of practice or deficient.
Last edited by CraigVIC on Tue 20 Oct, 2020 5:56 pm, edited 1 time in total.
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Re: GPS: 'the good, bad & ugly' article

Postby commando » Tue 20 Oct, 2020 3:59 pm

Been around PLGR's (precision lightweight GPS Receiver) long enough and if you call 2.75 lbs light, the designer has never been hiking.
also I don't want to put military capabilities in a global google bot watched forum.
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GPS: 'the good, bad & ugly' article

Postby GPSGuided » Tue 20 Oct, 2020 10:37 pm

I'd suggest that article is way out dated, back to the days when there was only GPS. With the latest iPhone 12 series release and for a few years prior in some Android smartphones, our pocket guidance devices have incorporated multiple, and now 4 independent satellite guidance networks. US’s GPS was first, then there was GLONASS, Galileo and now Beidou. So altogether 4 networks, each with 20-30 odd satellites up there, I’d think our handheld consumer units would be cross referencing each and every one of them to give us the most accurate pin point location. GPS is no longer the only boy in town and any attempt by the US military to alter the GPS signal may now be mitigated by data from the other 3. I think we are fortunate to be served by 4 such systems when we are out there keeping us on track.


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Re: GPS: 'the good, bad & ugly' article

Postby keithy » Fri 23 Oct, 2020 12:52 am

Not much new in that article. I agree with Warin on the misstatements about PLB and GPS. Currently Cospas-Sarsat system doesn't do the GPS location, nor does the GPS system correspond with PLBs. The GPS chip within PLB devices determines the location based on the GPS satellites, and this information is also transmitted via the Cospas-Sarsat satellites to ground stations. The GPS III upgrade will include some S&R capabilities, but I haven't read up on how that will work. Additionally while GPS satellites do have a secondary payload capable of detecting nuclear explosions, but the results of these are not available to consumer GPS units (just curious why it was mentioned for bushwalking).

This is going to be one of my long winded replies but these are just some of my thoughts on the articles' points:

The GOOD
The other "good" mentioned is the inclusion of WAAS or EGNOS for position augmentation (basically ground or space based systems that reduce the error from GPS signals to aid in improved accuracy). Unfortuntately as at 2020 we still do not have either a ground (GBAS) or space (SBAS) based augmentation system for wide use in Australia. There was testing of a SBAS for AU/NZ but I haven't followed up what's happened with it.

"Are you standing on the left side of the trail, or the right? And do you need a smartphone to tell you? "


If it's the author's intentions to question the need for greater accuracy, I've heard this argument before when discussing improving GPS accuracy. What's wrong with improvements? Sure, bushwalkers and hikers might not need centimetre accuracy, but you've got to realise that the system isn't just designed solely for hikers or bushwalking? This to me is akin to someone saying why use a bicycle when your legs work fine. Hey, why use a bicycle when the horse is right there. Why use the car when you have that horse buggy, etc. I've mentioned upcoming GPS signal improvements before viewtopic.php?f=21&t=27459 I think these improvements will be great for civilian use.

Currently with most handheld GPS devices, you will be limited to using GPS or GLONASS and maybe Galileo constillations. But if you use a smartphone, the integrated GPS chipsets (usually now part of a System on Chip SoC with other processors) will give you access to GPS/GLONASS/Galileo/Beidou constellations. Some of my phones pick up the Japanese QZSS and although the Indian IRNSS is up I haven't seen that their satellites pop up on my phones.

And that was the extent of "The Good" in that article. Even when restricting the conversation on the benefits of GPS for hikers, I'm surprised that there is no more mention of anything else deemed "good".

The BAD
I have been in canyons with 800m-1000m walls on either side. I know that this will result in a GPS signal with poor accuracy. Indeed when testing out a cold start on a GPS in a canyon in Montenegro I stopped to see the impact if I timed it to see how long it would take being stationary in a narrow canyon, and gave up after half an hour of not getting signal acquisition. I was along the Moraca river north of Podgorica. One side goes up to steeply to about 1500m and the other side over the river goes up to about 1000m. But however, moving out of the tight canyon to a slightly more open area, signal was acquired quicker, and while accuracy was affected, it was not kms away from actual location. You can test your equipment in CBDs with high towers in narrow streets too. This creates the same multipath errors where the GPS's radio signal bounces off buildings. Depending on your equipment especially the antennas incorporated within, this too can impact signal acquisition time and accuracy.

"Smartphones and similar consumer devices are especially vulnerable."


I have tested various models of GPS units with different antennas from Garmin's protruding helix antenna, to the tiny patch antennas, to the wire antennas around the frame to external mcx antennas in the field. I have also tested various cheap and expensive smartphones with their GPS antennas sometimes doing double duty for all wireless communications, and their GPS chipsets integrated onboard a chip with other processors. All my smartphone testing is without a simcard, fully offline, with no wifi. With newer kit in the past 5 years, I haven't seen much differential in the "vulnerabilities" of this over dedicated GPS handheld units.

GPS has been around for 30 years. The errors mentioned have been there for a while, and are indeed in most user manuals. In "the good" sections there seemed to be criticism of the GPS improvements that seek to address some of the weakness of "the bad" in the current band.

The times I've heard of people getting lost by GPS were mainly due to user error.

Back when GPS units were non-mapping units, and displayed only location coordinates and a rudimentary breadcrumb trail, it was important to make sure you set the datum on the GPS unit that corresponded with the paper maps you were using. The wrong datum, in Aust especially with AGD66 and GDA94 meant that you could be 200m away from your intended location.

Of course, if you set the waypoints on the GPS unit while you were at a location, it would still lead you back to that location, regardless of what datums are set. Example :
  • You are using a non-mapping GPS unit.
  • You arrive at a campsite, the GPS is on with strong satellite lock.
  • You save the waypoint of the campsite on the GPS unit and go off for a day hike.
  • You can still navigate back to the campsite waypoint saved on the GPS regardless of whether the datum set on the unit matches your paper maps.

However, if you manually enter the coordinates from a paper map while having an incorrect datum set, this will mean your saved waypoint is incorrect. Example:
  • You use an older paper map with AGD66 datum.
  • On the map you locate a hut/campsite and manually write that location down.
  • The GPS unit datum is incorrectly set to GDA94 or WGS84
  • You manually enter the location derived from the paper map into the GPS.
  • When you arrive at the manually created waypoint set, you find that this is not the intended location.

There are glitches with maps, of course, as illustrated in http://bushwalk.com/forum/viewtopic.php ... 57#p293328 and viewtopic.php?f=21&t=30162, with the clear issues in Garmin's official V4 & V5 maps. I had no issue with the V3, other than the lack of details at times, and used that for quite a spell. I use a multitude of digital maps these days, from various sources, open sourced and government agency derived, and various printed paper maps that I have scanned and digitally georeferenced. Of course errors could be introduced when in my georeference of scanned maps, but hiking somewhere I have never been before, I will check my maps against various sources.

The author even states "Even USGS Topo maps have varying standards for accuracy." I've seen this with bought maps in Europe and South America that do not have detail or are inaccurate in some areas where I've walked. I'm not sure how this is a criticism of a GPS system however. Many more times only available paper maps have been large scale maps that were just ok for basic planning and navigation, but lacking in details for bushwalking, and I've used more detailed digital Open Sourced Maps instead.

Finally, the issue of batteries and electronics failures. Of course they can break and fail unexpectedly, the chip can fry, the battery can explode. For me, I have a redundancy in usually another digital device, with the same maps, and in the event of a global electro magnetic pulse event, I have a paper map as a backup. But EMP events aside, many of us bushwalking users of electronic equipment, GPS/cameras/readers/UV purifiers have alternate recharge systems for long hikes, from external powerbanks to solar options.

For longer hikes the option of digital maps is attractive to me as an alternative to carrying sets of multiple paper maps. The ability to zoom in and out quickly to plan the next day to create a route or alternate route (and have it calculate the length of the route automatically vs manually measuring the distance on a paper map), mark water sources and potential campsites as digital waypoints. Who hasn't had a non-laminated map get wet and damaged, and the crease points so worn that you can no longer read the details in the crease. Or have got to a point and realised that the map set required for the next few days isn't with the other maps.

The Ugly
Sure, GPS spoofing and jamming are definitely issues. The GPS signal is a relatively weak radio frequency and susceptible to interference. The improvements to the GPS standard seeks to improve it, again, I take issue with the author's stated "Are you standing on the left side of the trail, or the right? And do you need a smartphone to tell you? ", given the GPS III upgrade seeks to improve accuracy.

On potential jamming, I've actually experienced some odd GPS behaviour from my units in certain parts of the world. In Eastern Latvia and part of Estonia I had issues with my Garmin, even down in Turkey on the Mediterranean. In Latvia my Garmin wouldn't get a signal at all in a relatively clear non wooded area. I gave up after over an hour. Not sure if jamming as there was some weak signal showing up.

At the time, I had asked around on and it may have been due to jammers used due to conflicts in the area. So much so that there were maritime and aviation alerts to this occurring for planes and ships relying on GPS for navigation when going through these areas. This may have been the case for Turkey, but it didn't explain the situation I had with the Garmin in Latvia. I thought I was far enough away from the Russo Ukrainian issues for GPS not to be affected, but apparently it might have been an issue. The same GPS worked fine in South East Asia a few weeks later on the way back home.

Then last year I was in Georgia in the Caucasus mountains, with one hike taking me to the mountains some 3kms from the Russian border. I had expected to have some GPS issues, but had no problems there. Clear and accurate GPS signal.

I've never had signal acquisition weirdness in Australia so far - other than the usual poor position locations like canyons or under heavy foliage. Maybe when the war with New Zealand finally happens and they invade we might have some issues with GPS jamming out bush.

If I was to write this sort of article, I'd focus on the Good:
  • Quick determination of your horizontal position, even surrounded by fog where you are unable to view landmarks from which to take compass bearings.
  • Automatic track recording
  • Ease of saving waypoints points of interest for other hikers/future use (eg. trail conditions/hazards).
  • Ease of measuring distances - not just a straight line "as the crow flies" but along a winding route.
  • Ability to store multiple maps at various scales
  • Updated digital OSM maps can provide more updated landscape/trail information than printed maps.
  • Provision of GPS positions via PLBs or via SPOT or other rescue communication systems can improve rescue recovery.
  • Availability of geo referenced topographical maps from various sources (government land authorities and open sources). In the early days of mapping GPS units, I would have said that map costs and availability would have put this in "The Bad" column, but these days, there are multiple sources of accurate digital topo maps sometimes for free.
On The bad
Users need to understand the limitations of their devices regarding their immediate location and the GPS accuracy. Not all GPS have an "accuracy" detailed in prominent way. Garmin units typically put it in their satellite information page. This is where the device will give an estimate of the error. In poor locations you might see an error up to 100m. Obviously this means that your actual position may be up to a 100m radius away from its actual.

Some devices have antennas that can impact on accuracy and time to first fix. Some have significant GPS "drift". This means that in tracking mode, you might see the GPS track log move around while you are stationary. The poorer the signal strength, the larger the drift.

Some GPS devices do not have all Datum settings, or even the ability to change datums (like some early Suunto GPS watch models!). Datums settings matter when you are referring to a paper map or referring your coordinates to someone else. If you use and mark waypoints wholly in the GPS unit, the example I mentioned above you can see that you can use the GPS for navigation successfully regardless of your datum setting. With the adoption of the GDA2020 it will bring it closer to the widely adopted as default WGS84.

Battery life of newer models with fancier touch screens is an issue. The more features the newer touch screens models have, the shorter the battery life will be. Handheld GPS models with built-in lithium batteries will suffer the same issue that current smartphones have. They will have built-in obsolescence unless the battery can be replaced. Smartphones have an advantage here as they are used and charged daily. A recharegable lithium battery sitting in an unused GPS does not mean that the battery will last longer. Lithium battery technology currently means that leaving lithium batteries fully charged or fully discharged for long periods of time can have a detrimental impact on the overall longevity of the battery. The current rule of thumb is if you leave a device unused for long periods, discharge it to about 40% before shutting off. This is better than leaving it at 100% or at 0% for long periods. Some manufacturers state to discharge to around 50-60% if not using the device for long periods.

Limiting Damage - I've broken Garmin handhelds from carelessness, remedied now by having at least one or two anchor points to my person or pack, and a rubber guard for bumps. I've lost a smartphone from water penetration for simply not putting it in a plastic bag when trying to descend in a thunderstorm. Much like preventive measures like a water proof map case can protect paper maps, and a secured lanyard to stop you dropping a compass, there are things you can do to limit damage to your equipment.

If users understand these limitations, I believe the "bad" can be managed.

The Ugly
GPS jammers exist. As do wifi/phone signal jammers. GPS jammers like sometimes used in vehicles are usually low powered, and have a range of around 5 to 10 meters where they send out radio signals on the same frequency as the GPS signal. They have been used for illegal reasons, like a truck driver trying to hide his location from his employer who has GPS trackers in vehicles. They are illegal pretty much everywhere. Military use GPS jammers as well, and sometimes if you happen to hike near military sites, or if there are events nearby the US military for example will warn of GPS disruptions in particular locations. Of course, military use of jammers will be higher powered than the ones mentioned that can be cobbled together for a few bucks.

The same goes for GPS spoofing. If these are in operation, I fear there will have bigger issues than not being able to navigate by GPS in the bush.

I fear bushwalking in the zombie nuclear apocalypse, where we might have to navigate around zombie marsupials without GPS as the satellites were taken down in the preceding global conflict, and the EMPs took out the rest of the electronics. My eyes are no longer what they used to be, and I fear that navigating by the stars might be difficult due to degrading eyesight and the nuclear fallout clouds that block much of the sky.

Ok, that last part was mostly facetious.

I am all for learning the basics of navigation, compass and map, or by the stars, sextants and charts but there are still advantages of navigating with GPS. That situation I mentioned above, where I was unable to get a GPS signal on my Garmin. I still ended up using the digital map, zooming in, marking my approximate location and marking my progress where I could navigate on the map.

Again, I think it is important to learn the fundamentals of map navigation, whether by paper map or digital map. As a tool for bushwalking, I have long gravitated from using a paper map/compass as primary navigation aid to using the GPS as primary, and paper maps as my third backup. And these days I've also moved from dedicated handheld GPS devices to smartphones. My last pre-pandemic long trip, I have left the Garmin handhelds at home, and taken my smartphones instead.
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