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iPhone 11 and above have a U1 chip which is supposed to be much more accurate than phones without that chip.  It uses UltraWideBand technology and (I read somewhere) it will get down to 30 cm.  Here shown is a plot done with geo data (Details tab) from an iPhone 6 (no U1) photo.    Has anyone tested a U1?


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  • mceclip0
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I am copying the posts from the previous thread (which had a title not descriptive of the current discussion) below. Please continue the discussion on this thread.

Admin wrote:
Oscar, I don't understand what you are showing in your photo.

oscarwagner wrote:
I took my iPhone 6 to a manport about 600 feet from my house with the phone OFF. That manport can easily be seen on GE so it could be located later on. I stood on the manport, turned on the phone and started taking pictures about every 4 seconds. Turning on at the port is only important to learn how long it takes to get to GPS lock after travel. I loaded each of the photos onto my Desktop, right clicked, selected properties and clicked the Details tab and scrolled down to lattitude and longtitude. This time all but the first of the photo coordinates were about 15' SE of the manport. To locate them, I opened a "placemark" and maneuvered it till the coords matched the photo. Quick check says 1/100th of a " (second) is about one foot. The U1 chip in the iPhone 11 and 12 is supposed to do much better than a nominal 15'. I want to know how much better.

Admin wrote:
Thanks for the explanation.

Another good test to do would be to go out a couple months after the first test and repeat the process to see how much the points have moved. If they haven't moved much then your device is still useful for locating waypoints you established earlier, even if it has large absolute error.

duanerussell wrote:
It appears that precision is not gained after about 15 seconds of the phone acquiring the satellites. The variation in locations also tells me that 1) there is something nearby causing satellite-signal bounce, or 2) the algorithm doesn't get good accuracy. Close, but not repeatable to great precision. I would have thought it would have taken a bit longer for the phone to have that close of a cluster.

Still, not bad for a phone. It will be interesting to see if someone with a newer model can do the same, but get a tighter cluster of locations. I will have to try it with my Galaxy S7 Android.

In response to your second question:

"Somewhat on same subject: What is your favorite iPhone app for plotting points while riding or hiking?"

I use Solocator to take photos of my split points. The app stamps the photo with GPS data and any other labels I attach to the photo (split name, course name, my business name). I then supply these photos to my clients.

Example below.

Cowtown 10K 2020 Mile 5


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  • Cowtown 10K 2020 Mile 5
Last edited by garybrumley

Went out and bought an iPhone 12 Pro to test.  It does better than the 6 BUT my buddy was just lucky that day.  I do get about 20% closer with the 12.  It will come in handy mapping out new trails not yet on Google Earth.  Using the Solocator app shows accuracy before the shot. Best for the 6 was +-16 feet and the 12 says 9 some of the time but almost always does 13 feet.  The 12 is a lot faster.  I am guessing it throws off fewer wild readings because it locks onto satellites faster.  Solocator takes about 3 seconds to finish a picture and the iPhone 6 takes 3 or 4 times that long.   So between faster satellite lock and knowing guessed at accuracy, I have had no wild readings with Solocator saying +-13 feet.  Taking 2 shots of important points helps verify accuracy. 

Now, fess up time: the U1 chip is likely not involved in any accuracy improvements.  It is supposed to let you put an active tag (Tile) on something and get within a foot of it over a WiFi like range, say 150 feet.  Tiles are $25+.  Remember the the old shoe chips and the threat of a $35 "fine" if you did not return it?

The LIDAR function works and really gets distances < 16 feet.  Still, nothing you would use to mark a 2 x 4.  Quite disappointed at how little the sales people knew about these functions.

Keep realizing more things Gary Brumley's discovered Solocator can do faster and better.  This is a shot of a reference bench leg that has the radial to the S F point right there and included.  No more, "Oops, I forgot to record that."

Not sure how but it could make triangulation easy for faster, more accurate descriptions.  I have asked the author if his app could generate actual links to a map location.  Fewer and fewer people keep a regular computer and printer around.  At $10,000 / gallon (my accountant cousin's calculation) HP inkject ink is a tougher and tougher sell.  It is so expensive that you are afraid to use it and when you do, it has dried up!  The world is going mobile. A big part of service to our customers is making it easy for them to find stuff the morning of the race.


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  • mceclip0
Last edited by oscarwagner

Thanks Oscar for bringing this topic up. We're all using GPS for multiple purposes these days, so whatever we can learn about its accuracy is very important.

For single point location, what we are call "accuracy" depends on your purpose. If your purpose is to drop a waypoint with your device at a mile mark and then 2 years later use that same device to find that location, then repeatability of your device is all that matters. As long as it sends you to that same location it doesn't matter if the GPS coordinates it assigns to that point are accurate or not.

If however, your purpose is to determine the GPS coordinates of a mile mark, and then give those coordinates to a race director so he can use them with his device to determine the location of the mile mark, then absolute accuracy of BOTH devices is important. In that case we need to consider the accuracy not just of the latest and greatest devices, but also the less expensive and older devices that race directors might have in their pockets.

With all that in mind, and now that it's warmer, I'm going to do an experiment similar to Oscar's. Except that I'm going to take multiple readings over time, probably about once a week. I'm curious how the accuracy of different devices will be different, and also how repeatable the reading of each device will be over time. If you're interested you can follow the experiment at the link below as I add new readings each week.

Last edited by Admin

For the benefit of an "old guy", how many of your race directors can use GPS coordinates at all?  I can't think of any that I've measured for.  Additionally, I am sure that mile splits are established on race day by pacing from a permanent landmark.

If I understand Oscar's very well done work, I could use my phone to provide a GPS Coordinate set that I could record by opening Maps or Google Maps (iPhone 11) and marking the location where the phone is.  I could send these coordinates to a race director who could go to the same spot using Maps or Google Maps.  How close to the original spot is the subject of Oscar's work.  I agree that if the process was accurate within say 1-ft and repeatable also within 1-ft, it would indeed be very valuable.  It could still, even now help locate a paint mark on a country road with no convenient landmarks.  The caveat here is that the GPS coordinates must be used to find a permanent (paint included) landmark.

On a trail, or in the woods, maybe not so much.

"Close enough to find the landmark used to locate the split" is another measure of accuracy. But I would say any device that does GPS is accurate enough for that. It doesn't really matter if the device gets you within 1 meter or 15 meters.

There are some courses though, like ones that are primarily on bike paths through parks or on rails to trails, that don't have many landmarks. For those GPS is really the only thing you can use to define the split location. And therefore, accuracy matters.

Over the past 3 weeks I've taken GPS readings each week from 3 different devices and put them on the map I shared before. So far the  newer and much more expensive iPhone does appear to do better than my cheap, old Android device.

My learning style is confabulation: make something semi-logical up and learn the truth when people crawl out of the woodwork to shoot you down: "The LIDAR function works and really gets distances < 16 feet.  Still, nothing you would use to mark a 2 x 4.  Quite disappointed at how little the sales people knew about these functions." 

That is BAD wrong!  About 50 yards fom my truck yesterday morning with no tape and needed to describe a mile mark from a point about 50' away.  Wondered if the 16' LIDAR limit could be used in multiples.  Tried it and worked fine BUT also noticed that with the right app, you could keep going.  Just now went out into street to my steel taped 200' horseback course and tried it.  Fixed one point and started walking.  Was admonished to move slower once but at the end, without trying for precision, it said 200' 2".  No idea what limit it is but this should work fine for description of miles at least that far.


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  • mceclip0

It gets even more astonishing.  Next obvious question WAS: Will it go around corners or through objects?  Ran a 25'  tape under center line of my truck.  Set one end at zero point of the tape, walked around vehicle and the set other point at 22' and took picture.  A Riegel Hub at counts per rev on a 27" tire resolves down to about 3".


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  • mceclip0

Hello ADMIN:  Which phone are you using to get coordinates?  Do you check "accuracy"  with app like Solocator before recording?  On my 12, I get fluctuating 9' and 13' indications.  You seem to be proving the point that if the accuracy is right though, eventually indicated points will surround the correct point. 

"Measure" app thing just gets crazier.  Guy at work showed me "Measure" on his iPhone6 (probably a 6S) yesterday and it did fine on 10'.  Net says you can run it on any machine with IOS 12.0 or newer which it goes on to say it iPhone6S or later.  This is the icon.So you may be able to use this with much less phone than I thought. 

I tried it on 1,000' cal course and got 998' 5" moving maybe 3 feet / sec.  Confusing info on Apple website talks about using LiDAR right next to info about this app but you can do a lot with a much older phone and plain old Measure app. 


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  • mceclip0

I'm using a Moto G5 (cheap phone), and iPhone 8 (expensive phone) and a Garmin handheld device (expensive). My main interest is finding out how consistent and accurate my device (the handheld) is over time, and finding the same for some random device (cheap or expensive) a race director might be using to set up the course.

I have little control over the device or the app the race director will be using, especially if it's a new RD 7 years after I certified the course. It's possible that RD will be using a cheap phone with the first free GPS app he happens to come across. That worst case scenario is what I'm interested in testing. If we provide only GPS coordinates for a mile mark because it's in the middle of nowhere, how far off will that mark be when an RD sets it up?

I have dutifully located splits with measurements from nearby fixed objects during certification rides, then located these points as well as possible in GE -  considering the parallax offset inherent in GE ground level (where available) vs. aerial imagery. I have then reproduced these points on my course map or on my timing points appendix. This seems to be adequate for locating non-certified splits. The process entails toggling back-and-forth between views, then marking a line with the ruler, which can be seen on both the ground-level and the aerial views.

However, I have yet to hear that any client has ever used these coordinates. I have discontinued making this effort until I know that clients want or need it.

Thanks for the heads up on Solocator, Gary. I see that there is now an Android version. Though the coordinates don't seem to be very useful for clients - yet - that day is coming. And the rest of the app benefits seem worthwhile.

Last edited by Race Resources LLC

I don't know of any clients who use them, but I have. I assist as course manager for a couple of half marathons that I also measured, and are run on Rails to Trails and recreational paths. Several splits are in the middle of nowhere. If you use the decimal format for your coordinates, it is easy to reenter into Google Maps and Maps will take you to within a few feet of your split. Close enough to find a tree, faded paint mark, nail or other feature. I also find it easier for a half marathon or shorter course to simply calibrate my bike and ride the course from start to finish and freshen the marks. 

Example: A GPS locater app on my Samsung S10 gave me the following coordinates for a round storm drain near my house of:  (41.820312, -88.169990).  The Solocater app for the same point gave me (41.820340, -88.169985).  If you enter either of those in Google Maps, it will take you to within about 4 meters of the storm drain on the SE corner of Main and 2nd Street.

GE coordinates for the same storm drain are: (41.820302, -88.170000)

This past weekend I setup a half marathon course using GPS coordinates. I measured and marked the course three weeks earlier but about half of the course and my marks were covered in leaves. A problem this time of year. I used a Carryall with all the course signage, mile markers and direction arrows so I did not have my bike and Jones counter to locate marks. Eight of the mile marks were visible or found by easy reference to close landmarks. Six of them had the leaf problem and no close landmark. I used the GPS coordinates that I had recorded when I measured the course and entered them into Google Maps, hit Directions and Start. When the guy in Google said I had arrived at my destination, I stopped and started kicking leaves off the trail with my foot. (Note to self – next time bring a broom or battery powered leaf blower) I found all the hidden marks easily without trying to locate some distant bridge or utility pole and then measuring to the mark. This is easy enough for any RD or course manager worth their salt to locate mile splits using only a good Smartphone.

In preparation for relocating splits with my GPS points for a client tomorrow, I've entered them all into Google maps and copied and pasted the google maps location link into a document. I wonder if more RD's would use GPS reference points if they were in a clickable document rather than having to enter all the numbers themselves into a map application.

I record GPS coords for splits with a Garmin 550t handheld (*.gpx), then copy/paste each split's coords (decimal degree format - DD) to a Google Sheet along with my split description. The coords can easily be copy/pasted into Google Maps for location 'on the fly' by whoever setting up the course and/or re-marking splits

In addition I use the GPS coords to edit/update "preliminary" splits in a Google My Maps map of the course, which is also provided to the client as a work product. A screen snip of the My Maps route is then used as the template for the map used for the USATF Measurement Certificate.


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  • GPS Coords

Ok, I see. My Garmin Oregon 550t (discontinued) seems to find satellites with no problem depending on where I am, of course. WAAS can be turned off if # of linked satellite is an issue. Previously I recorded geotagged images but now only take waypoints which are conveniently filed sequentially in a gpx file that can be directly uploaded into Earth for split mapping. In Earth I edit the default icon to a custom icon that reflects the mile (or km) number.

Not sure what workshop in April you're referring to. More info on that would be appreciated.

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