The choice of vehicle affects the gps signal (?!)

I capture my sequences mainly from a bicycle, less often from a car, public transport. And the accuracy of the gps track periodically upsets me greatly, although I studied and tested all the settings.
It would seem that the bike does not have a metal roof that can distort the signal … But the tracks turn out just awful …
The other day I had a long city trip by car, I fixed the external gps antenna at the lower edge of the windshield, and … the tracks turned out to be perfect!
What’s the matter?
Is the bicycle steering wheel distorting the signal? !!

Distorted path when riding a bike.
The true route is highlighted in red.

Almost perfect tracks recorded from a car among high-rise buildings

Does the GPS receiver has the same clear sky view in booth cases? Usually, in care beyond the windscreen , the GPS has an overall good sky view. On bicycle, where is your GPS? Don’t you cover it with your own body. Moreover, with care, you’re far from trees while with bicycle, you may be under trees, especially in your samples.

1 Like

looks like the gps receiver’s fault - overcorrecting for a bicycle?
I presume yours has glonass, and I also presume you don’t have any military installations possibly affecting gps accuracy in Barnaul

1 Like

I agree with this question. Several of the places you bike are so close to buildings or trees that a car could not go there. Even on the roads in the same areas, the car would often be more in the middle of the opening and have a broader view of the Sky.

Two of the main GPS problems are lack of clear view of the Sky and signal reflections from buildings.

Going from one side of the road to the other, can cause a challenge if there are trees or buildings close to you. Effectively the GPS has to lock onto several new sattelistes, resulting in lower accuracy for some time.

What can you do? Try to mount a pole on your bike and put the antenna on top of that. Even if it can get 1½ meters higher it may improve the signal.


On a bicycle, it is secured in a separate bag at the helm.
In the cab of the car, much of the sky was covered with a metal roof. Convertibles in our climate are unpopular), awning roofs are also rare.

The most productive receiver works only with gps.
Perhaps your 2 point is insignificant)
Not quite clear hint of cycle settings

Thank you, I was thinking about raising the external antenna, and yet these distortions are shocking. Yet the car moves faster than the bike.
Speed is good for gps accuracy?

There are filters that are applied to the GPS readings. I would not be surprised if these assume it’s possible to make a tight turn at 20 km/h but not at 50 km/h. Though your traces don’t really have sharp turns.

Also some GPSes automatically clip the traces to the nearest road when in “car” mode. But I don’t know how they determine if they are in car mode and in fact it may actually be hard-coded. So it may well not be the issue here.

Sometimes GPSes get more accurate after running a while. Maybe that explains the difference between your traces?

I had a look at Barnaul. Buildings are high enough to hide part of the sky. There are also a lot of trees that will disturb satellites reception. The first action you can do is, at starting of acquisition, to stay in an open area to catch a maximum number of satellites. So, when a satellite is hidden and back in view, it is faster catch again. The second thing to do is to check the accuracy announced by the receiver while moving. It may give hints on areas with bad tracking and allows comparison between bike and care.

1 Like

Thanks! Yes, this is called updating the almanac, ephemeris, etc., I heard this

One point that wasn’t mentioned yet: Some types of antennas work significantly better if they are put on a flat, electrically conductive surface. The technical term for this is “ground plane”. These antennas typically have a magnet in its foot so it can be firmly attached to the ground plane.

Maybe the placement of the antenna in/on the car was better regarding conducting surfaces that could act as ground plane?

Also note that GPS antennas usually are directed, meaning if they have two similar sides, only one is suited to be pointed towards the sky.

On a related note: I also encountered cases myself where GPS accuracy wasn’t satisfactory. Usually positioning errors from different loggers aren’t (completely) correlated, meaning you can record tracks with multiple devices at the same time (e.g. GPS logger and your cellphone) and then average them to get increased accuracy. I wrote this script to do exactly this:

1 Like

Thank. Interesting idea. Yes, my external antenna of this type. When traveling by car, it was located under the windshield on a plastic panel. On the tram, the antenna’s magnetization to the window sill did not work because of poor sky visibility and possible electrical interference.
It would be nice to create a DYA antenna, but a too thin core is needed in the connector.
Separately thanks for the script!

If you’re going to try the script, let me know if it worked for you…

1 Like

Sorry, I’m not good at programming. I have windows os, and in which program to insert your script?
It would be nice to move “graphically”, (left / right, etc.) inaccurate tracks with elementary operations as a simple graphic editor.
Maybe you meant this page.
Next, I get error 404 as a guest.

Sorry for joining late, didn’t really have an answer, just questions:
1/ it would help to know brand and model of the GPS and the external antenna
2/ did you try fitting the external antenna on top of your helmet, away from the electronics in the GPS receiver? When looking for a GPS, the advice was that in for example a Garmin Oregon there is a small antenna under the display, while for example the GPSmap series have a larger antenna in the ’ finger’ which sticks out on top.
3/ with the GPS mounted on the centre of the bicycle handlebars, notice that once the cycle comes to a stop, the indicated direction is all over the place - pointing in any possible -except the correct- direction; when hand-held, the direction is correct : seems the handlebars act as a distortion of the electromagnetic field - may similarly have some effect on the very weak radio signals?.
4/ comparing my tracks in a coach, on the bicycle and walking : the track on the motorway was almost perfect compared to the map, on the bicycle it jumps across the street between for example seven-story buildings, and while walking with the GPS on my hand (to the side, and in front, of my torso) the track can zig-zag anywhere - quite similar to your tracks.
Hope there’s something in this that can help you?

Also take note that satellite imagery may be slightly offset. Your GPS trace might have highly accurate parts where the imagery isn’t.

1 Garmin gpsmap 78+ garmin ga 25
2 No. I do not have a helmet and it is not mandatory. I can try to fix it around the collarbone.
3 I read this.
4 Thank you, I will try.