preferdownhill

I'm curious if there is any good app that can show realtime distance between two people. I've tried the paid version of ridewithgps and whatsapp and quite a few other apps. The lag times are are pretty high and results doen't update quickly enough to be useful. does anyone know of a preferably free app that measures distance that way. it needs to be free since i need to convince someone else to try to use it. I do some coding and i'm curious about possibly writing an app that helps me understand where the lag time occurs with these kinds of apps.

Steve B.

Elvo

jadocs

Wahoo Elemnt Bolt does it as well.

John_V 

I have used pretty much all of the cycling apps (for an iPhone) and have not seen any that do what it is you are wanting to do. If there is an app out there that has this feature, I'm sure it's not going to be part of their free offering. An issue that I can see is the distance between the group leader and the sweep. If you are talking 10 or so riders in a group, I don't think you will be able to distinguish, with any accuracy, the distance between the two.

On my Bolt, I can see other riders that are using a Bolt or an Elemnt but as the image above shows, the riders are further away than just a few riders behind. If a rider in my group has a Bolt, the tag are usually on top of each other so you really can't tell what the exact distance is.

Seattle Forrest

​​​​​​I would love to hear what you come up with if you go this route.

preferdownhill

the only thing i'm worried about is many of the places we ride have poor data connections. Maybe someone has a acoustic coupler for a 2way radio!!

I'm looking at a really simple desgin, maybe just 2 big numbers on the screen, speed and distance between lead and sweep. mabye some other stats at the bottom like moving time, and stopped time. maybe moving speed and overall speed. and if the ride is stopped, how long its been stopped.

John_V 

I've done a lot of coding for GPS devices and in the case of data lags, I can almost guarantee you the lag time is in how the GPS data is parsed by the programmer.

GPS data comes in packets called "paragraphs" that are nothing more than byte arrays that were created by converting the GPS radio signal. There are six sentences to a paragraph and each paragraph is a separate signal sent by the GPS satellite. Each sentence contains different data and usually the data you want or need is most likely located in two or more sentences. You have to know which sentence you are looking for as each sentence starts off with a different "word" (header) to distinguish it from the others in the paragraph. Once you find the sentence, you have to parse it and grab the data you need, do any conversions you need to make and grab the next sentence and repeat if you need data from that sentence. You will also need to know what position the data you need is located in the converted byte array. This has to be done in the time slice allocated to that process by the CPU because the app also has to grab data from any sensors that are being used, process that data and display the results along with the GPS data.

Now when that's done, you are going to have to figure out how to get the sweeps location, compare it to your location and determine the distance the two of you are apart. Good Luck!

Here's an example of a paragraph of data you will be getting after converting the byte array into readable string data that your app needs to use. The sentence start at the $ with the letters making up the rest of the word. Each comma separated item is a piece of data that you may/may not need to use in your app.

njkayaker

It seems that the phone (or Garmin) is doing all this work for you.

I don't think iOS gives you access to the data at the level you suspect programmers are making mistakes at.

There are lots of apps that do a good job at tracking. If that's the case, the problem with "lag"* is much later than what you are talking about.

* The "lag" problem isn't described anywhere near enough to try to fix it.

unterhausen

in an app tracking two riders, the lag certainly has to be in the two or 4 hops the data takes between the two devices. GPS->(cellphone->server->cellphone)->GPS

preferdownhill

android isn't really using that datagram approach for moving data, they are using classes and properties. one good thing around it is it helps with security and privacy, To use the class in the code the user has to give permission to the app.

as for determining distance between two latitude - longitude points, theres a pretty simple equation here: https://www.movable-type.co.uk/scripts/latlong.html . i tested it, using hundredths of minutes, its resolving down to just a couple feet. the equation is pretty cool, it considers the curvature of the earth in the distance, not just the absolute straight line between them. not that it matters at the distances i want to use.

there is some issue with how the two phones exchange the data, with polling or notifications. but thats the crux of what i want to play around with. i want to do a bunch of datalogging with it to see how tightly bound they can be without wasting data bandwidth.

the biggest issue is that alot of time we are out of range to cell towers. Its possible to do peer to peer with cell phones but range is limited, `300feet best case. It would be nice if there was some way to enhance p2p with some kind of 2way radio, then we could text message though the interface as well. I also looked at arduino devices. there are cheap and highly customizeable with enhanced antenna. probably can get up to 1000ft. they detect and broadcast gps data and cellphone app picks it up.

njkayaker

John_V's response was "interesting" (i.e., odd).

The effort doesn't seem worth it for such a small distance (1000 ft).

How many people are you tracking?

Some people have considered just using headset radios.

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

https://buy.garmin.com/en-US/US/p/533999#specs

Garmin needs to release a version of this that supports IQ apps.

Or buy collars for everybody...

https://buy.garmin.com/en-US/US/c12522-p1.html

unterhausen

those collars would be a great idea, particularly the ability to apply shocks to each other.

preferdownhill

there is a lot going on with drone tracking that looks promising for what I want.
I'm probably tracking 20 people.
i've considered handsets maybe i'll just get a pair.

I am curious if anyone is connecting arduinos using the same tech in handset radios.
then its possible to exchange gps info and text messages over a decent distance.

I'm interested in just doing enough work on it so I understand the issues and can talk to experts over the next couple years to keep up with whats changing,.

EDIT: was googling, apparently FCC doesn't allow data communications over 2way radio sytems, its reserved for human voice only.

njkayaker

Generally, that's line of sight (it's easier).

It seems the drone trackers are cellphones.

Highly unlikely.

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

The dog collars, bro. Exactly what you need.

I believe a transmitters can pair with more than one receiver.

unterhausen

there was a brand of inexpensive mesh computers that had a reasonable cell connection arrangement. Name of the company escapes me now though. You could use peer to peer communications until there is a big enough gap that you need to use cell. But that's a pretty serious programming project.

njkayaker

preferdownhill mentioned that idea already.

There is (was?) a company trying to that with cellphones that used software to leverage the hardware (BT and WiFI) the phones already have. But the range is very short.

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

The dog collars are (probably) ANT+ transmitters on steroids. If they are reliable, it's likely partly-due to that they only send small independent chunks of data. If you lose a chunk, it's no big deal.

John_V 

Not sure what was odd about it. OP said he knew some coding and would look into trying to do it himself. Having done several GPS projects for the government, I simply showed him what he had to do and where the biggest lag in retrieving GPS data lies. Regardless if you're using a phone or GPS computer, all GPS receivers convert the radio signal to byte arrays in packets that I gave an example of. This is a continuous data stream and the packets don't wait until they are processed. The byte array has to be parsed in order to extrapolate any data bits that you are going to work with. It doesn't matter where the parsing is done (OP's code, OS, third party classes and properties or whatever), someone has to write the code to do it. The longer it takes the code to parse the data, the greater the lag time and the more packets that pass through unprocessed. So with any app or device, regardless if it's a GPS app or not, any lag time between execution and display is always dependent on the/a programmer.

njkayaker

The lag he's talking about, it isn't with the GPS data!

Pretty-much any GPS will provide location much, much faster than he needs.

He doesn't have to do any of what you are talking about.

Any device that would be reasonable to use already does all the stuff you are talking about.

His problem isn't with the raw GPS data.