Athens80

Just curious -- how would you know that the altimeter in a model aircraft was particularly accurate? What known standards can you compare it to throughout a flight of several hours and many miles across the landscape?

andr0id

They are super sensitive and can detect pressure differences equivalent to inches of altitude change.
But... That is RELATIVE altitude which is not the same as elevation.

Pilots have to zero barometric altimeters when they leave the airport and they have to know the difference in elevation between where they are and where they are going (and in between) or the ground may come up to meet them even if the altimeter says zero.
Modern AC have radar altimeter also which pings the ground to give you above ground level AGL.

Improper settings of this stuff and not paying attention can lead to what they call "controlled flight into terrain."

Fly2High

In the end all I am getting at is the manufacturers, be it the R/C hobby stuff or Garmin, are reporting the accuracy and both are using Barometric pressure sensors for altitude determination. All I am getting at is that Garmin should buy the better sensors and use the ones with temp compensation built in if accuracy to their users is being complained about.

They have room for improvement is what I am pointing out.

As to the hobby stuff's accuracy, I have used them for alteration in altitude changes to fly model gliders with the intent to indicate lift. In this regard, they also work very well. If the sensors from the Garmin were to be used, they do not have the accuracy nor are they using a refresh rate capable of supporting variometer functionality. +/- 10 ft is rather poor.


As the above poster points out, all barometric sensor based altimeters are using relative altitude. You still need some reference point to say this pressure is at this altitude if altitude measurements are what you are after. If you are after changes in elevation, it is not so important.

Athens80

@Fly2High - Maybe there's just too much I don't know about this. andr0id's reply references altimeters and procedures in full-size aircraft, which are not in question here. How do you know that the hobby stuff you use would be more accurate in a cycling application? To this outsider it seems that it would have to have been proven more accurate against reliable elevations over a flight of several hours and many miles across the landscape. That seems like it may be a different (though related) test than whether or not an RC hobby plane pitches up or down over a short distance. It seems like a slight inaccuracy which would be irrelevant in the RC world could accumulate to big differences in the cycling GPS world.

Seattle Forrest

The two altimeter watches I've had have both done a better job than my Edge. Which is funny because one of them is a Garmin (Fenix 3). The other was a Suunto (Core). I can see the altimeter change a foot at a time going up or down stairs on the Garmin watch.

When I did Washington Pass my Fenix's reported total gain was off by about 40 feet out of 3,500; the next day on Cutthroat Pass it was wrong by 13 feet out of 2,300. Did both rides on bluebird days at about 50 F.

Fly2High

To me, Garmin needs to do temp compensation. These devices are hanging out on out bike in the sun all day. At stops and what not, the case is heating up. When we ride, it will cool down. All of this will throw off accuracy.

I know from flying the model planes, the fuse MUST have proper venting. If the air is coming in the wrong way it can create a positive or negative pressure inside the fuse throwing off the altimeter reading. Having no venting also throws off the readings. With the Garmin being waterproof, I wonder where is the venting to allow for pressure change within????

rm -rf

The starting elevation can be off by 300 to 500 feet when I turn on my Garmin 705. I assume it's air pressure changes since the last time I had it on.

The Garmin 705 can determine an accurate altitude by using the Save Location and it's Avg button. I let it average for about 60 seconds. The altitude converges to the the correct number as it gets more readings, and after about 20-30 seconds, it only changes by a couple of feet. The calculated elevation at my house is within 5 feet of the USGS topo map's elevation.

But the Garmin software never does this during a ride, even if I'm stopped. And it only looks at the stored locations if they are within 100 feet when I hit Start. And even a 10 second recalc when turned on would be way more accurate than it is now. Just lame software design. ( Another dumb design: if I stop on a hill while climbing, the reported grade keeps increasing each second-- 5%, 6%, 7%... How can you average in zero mph and zero elevation change and get an increasing grade?)

But I have seen very good results on some Blue Ridge Parkway rides. Starting with an accurate saved location elevation, I've stopped at overlooks after 10 miles and 2000 feet of elevation change, and it's often within 20-30 feet of the elevation reported on the sign.

botty kayer

Anyone else having issues with RWGPS not tracking properly over the last few days?

I'm a long time user, using the same phone and have not changed any settings, am riding in central London where I ride all the time so I know there is good reception, and I've checked and I do have the up to date version of the app so its not due any updates as far as I can see.

It's been working fine all year but my rides for yesterday and today are suddenly not being tracked properly, the trace is in jagged straight lines only doing an approximation of the route I actually rode, and as a result is missing a significant amount of data and missing miles off the actual route distance, so making all metric info, average speeds, mileage etc totally wrong.

I've submitted a query to RWGPS but wondered if anyone else has been having the same issue over recent days, maybe we due an update?

Iride01 

botty kayer

Seems like a question deserving of it's own new thread.

NJgreyhead

I don't know if it is worse lately. Maybe. It shows me going thru yards and across water, as opposed to roads.
I do know I am disappointed in my new-ish Garmin 830's accuracy on distance. Seems off about 1.3%, which is not much for my bike riding, but it is too much for my running. Maybe not the best tool for that, but it's what I already have, so I multi-purpose with it.

And yes, maybe another thread is the place for this. Or maybe we are just beating a dead horse.
Still, the state-of-the-art is not what I had hoped for.

Sy Reene

you carry an 830 on your runs? How have you determined the 1.3% error? Variations over the same route? just curious

NJgreyhead

Up until recently, I used bike computers when riding. I was always careful about calibrating them, doing the rollout x 3, then dividing by 3 to get an average, and always rolling out with my weight on the bike and the tires aired up to my typical psi to take into account tire deflection. And with two different bikes, and two different computers, my usual running course distance agreed between the two computers. But when I tested the course against the Garmin 830, the Garmin showed it as shorter on the several times I used it. It was also shorter with my previous Garmin 820 (but I don't recall if the two shortages agreed).

The other day I ran a 5k, an annual event run by a credible org, using regional timing association officials. I gotta figure, they had mapped out a proper 3.1 mile course. But my Garmin 830 showed the distance as 3.07 miles. If my calculation method is correct, the diff is .0130293.
Thinking back, I wish I'd checked the distance with an experienced runner I met who was wearing a smartwatch.

NJgreyhead

Taking a closer look at the route Garmin recorded on my run the other day, I noticed that, at one point, it shows my path almost on a parallel road, a block away from the road I was actually on.
Maybe that explains why yesterday on a bike ride I paid attention to the Garmin and ignored the cue sheet, only to have the Garmin give me an Off Course, U Turn warning about a half-block past the proper turn.
Disappointing.

Maelochs

No RWGPS errors in my part of the US in the past few days.

I never worry about precision ... to me it is like scales. I weigh myself, but how much do I weigh? Would I need to be in some International Bureau of Weights and Measures isolation chamber compensated for the exact number of feet from the center of the earth, or some such? Do they still have gold weights kept in vacuum chambers which determine grams, etc, or is it all electronic, like time, nowadays?

And how does that compare to the scale in my bathroom, at the gym, or at the supermarket?

I figure I use a consistent measurement and it is all relative to whatever I consider my "baseline." So .... if I ride pretty much the same route several days in a row, I get almost exactly the same distance, elevation change, and max incline .... that's good enough for me. I might be riding more or fewer feet up or down, or a greater or lesser pitch, or some feet more or less .... but so what?

When I ride terrain I have never covered before, I have two data sets .... the RWGPS data, which only makes sense when compared to known routes ... and my personal experience, which I can only compare to past experience. Also, though, RWGPS only gives me max elevation as a number, even though it does a line trace of grade. I might call a certain climb a "five-percent clime" but it might average half of that. I don't care, because for me the actual metric is "How much did it hurt today?"

mschwett 

a man with one watch knows the time (or at least he thinks he does...) and a man with two is never sure.

strava's explanation on the subject shows some of the complexity here. crappy GPS sensors (and the nature of GPS), varying basemaps, devices with and without barometric altimeters, changing weather...

https://support.strava.com/hc/en-us/...-Your-Activity

i don't pay much attention, my daily go-to ride varies from 1300 to 1700 feet depending on who i look at, and most rides are in that same 20% variance range. the only thing that annoys me consistently is that during route planning RwGPS has some really egregious errors in it's interpretation of the basemap. for example, it believes that if you ride across the golden gate bridge you instantly drop to sea level and then climb instantly back up on the other side of the straight. completely understandable - they're using the "ground" rather than the structure, which may not register in their basemap, but for a road crossed by thousands of cyclists a day every day for decades, an odd error. tunnels are similar - the route plan shows you climbing the hill OVER the tunnel a lot of the time!

njkayaker

"Basemap" is an odd term. Garmin uses that term for a very-basic map without much detail.

The maps that RWGPS uses (generally, Google or Openstreetmap) don't have elevation data at all.

RWGPS use a separate map for elevation using data that eveybod has access to (RWGPS isn't collecting elevation data itself**). That map just has elevation for the surface of the earth. It doesn't include profiles for things like bridges and buildings. The data was acquired on a space shuttle mission (among other spacy sources). So, roads in tunnels wouldn't be seen at all.

RWGPS isn't "making egregious errors in its interpretation". It's just using data that is limited.

==================

** Strava collects elevation data from people's uploaded rides, which they use to augment the widely-available elevation data. Give that Strava already deals with segments, it's a short step for them to deal with elevation from rides too.

mschwett 

basemap is the correct technical term (in GIS circles) for the underlying data (typically street-centerline and elevation dataset) on which a map of a specific subject (e.g. a bike ride) is created. not sure in what context garmin uses it.

i just noticed that RwGPS actually has a tool to correct for these errors in route plans:

https://ridewithgps.com/help/flatten-elevation

njkayaker

Garmon provides a map file that has limited data for the world that they call a "basemap".
​​​​​​
More people here might be more familiar with that map on the Garmin. Not many are going to be familiar with the GIS usage of the term.

https://www.gislounge.com/basemaps-defined/

RWGPS uses either Google or OSM (or some other) as "basemap" (it's not one). RWGPS calls them maps. RWGPS uses a DEM map to add, as a second step, elevation to routes.

Interesting. It just updates the particular route. Most people won't be bothered to use it.

mschwett 

yeah - annoying to have to do it over and over for different routes. ideally they’d have their own layer of “corrections” over the DEM data, with some streamlined process to accept or vet them from either user data or better elevational sources, e.g. many cities have openly available topographic data, sometimes for the entire city, usually for intersections, etc. there are too many roads in the world to expect perfection with this… but the golden gate bridge !?!

fooferdoggie 

my 1030+ will ahve the same altitude every time I arrive home it has auto correct and seems pretty consistent. I see about 20' difference I the same ride I take on my commute. one day it can be 310 another 320 or 33 5my garmin before it without auto correct was all over the place when I started a ride.

Seattle Forrest

Strava automatically runs their altitude correction over anything you send them unless the data says there was a barometer for elevation. Doesn't help much if your data is in a different place though.

Do you know how to use a barometer to estimate the height of a tall building? You can drop it from the roof, count how many seconds until it hits the ground, and then math it out. 🙂

mikethe

Maybe altimeter issues?

mschwett 

good to see that RwGPS has fixed this for route planning. i noticed it a few days or a week ago.