How to compute the length of a walk

[david bolster]

I use a Garmin for hiking. At the end of a walk it shows me what I have actually walked. Of course, most of the time I do not walk absolutely straight - trying to get the best footing. So, when I get home I connect it to the computer, and get a different number of miles for the walk. Which is right? What do other walkers us when writing a walk report? The length on a map, or what you actually walked on the day?

[Coop]

Normally plot a rough route on the wee etrex
When I finish a walk now I'll plot another route on the GPS following almost exactly the " track" I took.
It normally isn't that much up or down from the WH route( if I use that route) - unless it's a walk where I veer off, cut some off on a hill or go a bit further a little - for whatever reason.

[davekeiller]

It's worth having a look at the GPS points, and seeing whether you agree with them.
The GPS will calculate your location periodically and then join those points with straight lines to determine how far you walked. Depending on the frequency of location sampling, this can underestimate the true distance walked by cutting off corners. Also, depending on the quality of the GPS signal, sometimes the quoted locations differ slightly from your true position, generally leading to a slight variation between measured route length and actual route length.

[scoob999]

Your gps stats will be more accurate as it calculates as you go, once you download it onto a map it'll calculate from the contour lines, or at least that's my understanding of it

[david bolster]

Normally plot a rough route on the wee etrex
When I finish a walk now I'll plot another route on the GPS following almost exactly the " track" I took.
It normally isn't that much up or down from the WH route( if I use that route) - unless it's a walk where I veer off, cut some off on a hill or go a bit further a little - for whatever reason.

Thanks. Like you, I plot the route on my GPS in advance. But when I go to the computer and plot it on the map I find at least 10% variation. Some things are obvious, such as mistakes I make. Some are less obvious. E.g., basic geometry: - the line that goes up (or down) will be longer than than the horizontal. - Going uphill and downhill will automatically be more than the route on the map. Traditionally, walk lengths will have been estimated as to the route on the map (the horizontal). With a GPS they will now always be longer. It sounds as if everyone computes the walk length from the GPS rather than from the horizontal.

[david bolster]

It's worth having a look at the GPS points, and seeing whether you agree with them.
The GPS will calculate your location periodically and then join those points with straight lines to determine how far you walked. Depending on the frequency of location sampling, this can underestimate the true distance walked by cutting off corners. Also, depending on the quality of the GPS signal, sometimes the quoted locations differ slightly from your true position, generally leading to a slight variation between measured route length and actual route length.

Thanks. My Garmin is frequent (compared to smart phones). Yes, I do take a close view and edit them. I agree with you about "the true distance walked". This is usually quite different from the distance plotted on a map.
Some things are obvious, such as mistakes I make. Some are less obvious. E.g., basic geometry: - the line that goes up (or down) will be longer than than the horizontal. - Going uphill and downhill will automatically be more than the route on the map. Traditionally, walk lengths will have been estimated as to the route on the map (the horizontal). With a GPS they will now always be longer. It sounds as if everyone computes the walk length from the GPS rather than from the horizontal.

[david bolster]

Your gps stats will be more accurate as it calculates as you go, once you download it onto a map it'll calculate from the contour lines, or at least that's my understanding of it

I agree with you. Traditionally, the books we have used, computed walk lengths from the map. You have confirmed for me my guess that no one now does this. The difference can be as much as 20%. I am still left with the question as to what is reasonable to include in a walk length? E.g., on many paths, we all naturally wander a little, in order to find the best footing. I tend not to include that. I do that by reducing the number of waypoints. Also, I discount the height. I.e., basic geometry. - the line that goes up (or down) will be longer than than the horizontal. - Going uphill and downhill will automatically be more than the route on the map. Traditionally, walk lengths will have been estimated as to the route on the map (the horizontal). With a GPS they are now being calculated on the lines that are up or down. By putting my walk on the flat, I take out that extra that the GPS has included.

[maremalin]

Your gps stats will be more accurate as it calculates as you go, once you download it onto a map it'll calculate from the contour lines, or at least that's my understanding of it

GPS stats for sure will be more accurate - but settings of given GPS device are crucial too.
This is from test i did with different GPS sensitivity settings

Garmin Ultra Track mode, GPS+GLONASS and GPS only

Ultra Track mode is big hit and miss. I have used it successfully before but its not reliable
GPS + GLONASS - are best for accuracy - but at the same time this is power hungry
GPS in this test worked the best - except for that little river crossing bump that never happened it looks pretty accurate

[Lournieloon]

I use a Garmin for hiking. At the end of a walk it shows me what I have actually walked. Of course, most of the time I do not walk absolutely straight - trying to get the best footing. So, when I get home I connect it to the computer, and get a different number of miles for the walk. Which is right? What do other walkers us when writing a walk report? The length on a map, or what you actually walked on the day?

I thought most people on this site used Viewranger. I do, and record all my hikes and find it a useful aid, complimenting the maps I print off WH. I haven't questioned the accuracy of the gps tracking but a rough reckon up agrees in the main with other walkers walk reports.
I have downloaded a couple of others waypoints and on actually having done the trail, it pretty well ties up. Recent one of Ben Starav. The waypoints were pre the diversion at the start, for the privacy of the new occupants of the old schoolhouse. Apart from that spot on. Distance and time taken were witgin ball park figures. How precise is necessary?

[david bolster]

Your gps stats will be more accurate as it calculates as you go, once you download it onto a map it'll calculate from the contour lines, or at least that's my understanding of it

GPS stats for sure will be more accurate - but settings of given GPS device are crucial too.
This is from test i did with different GPS sensitivity settings

Garmin Ultra Track mode, GPS+GLONASS and GPS only

Capture.JPG

Ultra Track mode is big hit and miss. I have used it successfully before but its not reliable
GPS + GLONASS - are best for accuracy - but at the same time this is power hungry
GPS in this test worked the best - except for that little river crossing bump that never happened it looks pretty accurate

Thank you. That is so impressive!

[david bolster]

I use a Garmin for hiking. At the end of a walk it shows me what I have actually walked. Of course, most of the time I do not walk absolutely straight - trying to get the best footing. So, when I get home I connect it to the computer, and get a different number of miles for the walk. Which is right? What do other walkers us when writing a walk report? The length on a map, or what you actually walked on the day?

I thought most people on this site used Viewranger. I do, and record all my hikes and find it a useful aid, complimenting the maps I print off WH. I haven't questioned the accuracy of the gps tracking but a rough reckon up agrees in the main with other walkers walk reports.
I have downloaded a couple of others waypoints and on actually having done the trail, it pretty well ties up. Recent one of Ben Starav. The waypoints were pre the diversion at the start, for the privacy of the new occupants of the old schoolhouse. Apart from that spot on. Distance and time taken were witgin ball park figures. How precise is necessary?

Thank you. Actually, I am not asking for precision! I will have a look at 'viewranger'. I use Garmin basecamp. I will see how it compares. Friends use memory map. My question is in the opposite direction - should we include all the computations that a GPS give us? - e.g., altitude. My understanding is that for every 100 meters of elevation you can add 0.5 km to the length that is on the map.

[StevieC]

I use a Garmin for hiking. At the end of a walk it shows me what I have actually walked. Of course, most of the time I do not walk absolutely straight - trying to get the best footing. So, when I get home I connect it to the computer, and get a different number of miles for the walk. Which is right? What do other walkers us when writing a walk report? The length on a map, or what you actually walked on the day?

I thought most people on this site used Viewranger. I do, and record all my hikes and find it a useful aid, complimenting the maps I print off WH. I haven't questioned the accuracy of the gps tracking but a rough reckon up agrees in the main with other walkers walk reports.
I have downloaded a couple of others waypoints and on actually having done the trail, it pretty well ties up. Recent one of Ben Starav. The waypoints were pre the diversion at the start, for the privacy of the new occupants of the old schoolhouse. Apart from that spot on. Distance and time taken were witgin ball park figures. How precise is necessary?

Thank you. Actually, I am not asking for precision! I will have a look at 'viewranger'. I use Garmin basecamp. I will see how it compares. Friends use memory map. My question is in the opposite direction - should we include all the computations that a GPS give us? - e.g., altitude. My understanding is that for every 100 meters of elevation you can add 0.5 km to the length that is on the map.

Regarding the bit in bold, that doesn't sound right to me. Imagine a 1km walk that rises by 100m from start to finish. You can visualise this as a right-angled triangle...the base (i.e. the distance on the map) is 1000m, the straight end (i.e. the elevation) is 100m and so Pythagoras tells us that the hypotenuse - i.e. the distance you actually walked - is 1005 metres. In other words the uphill walk is 5 metres longer than it would be on the flat.

Apologies if I've misunderstood you, or indeed got my maths wrong!

[StevieC]

^^ Or to put it another way...if you climb Ben Lomond (5km distance on map, 1000m ascent)*, actual distance would be roughly 100m more than "map distance".

*Please note - all measurements are approximate!

[Lournieloon]

Thank you. Actually, I am not asking for precision! I will have a look at 'viewranger'. I use Garmin basecamp. I will see how it compares. Friends use memory map. My question is in the opposite direction - should we include all the computations that a ] give us? - e.g., altitude. My understanding is that for every 100 meters of elevation you can add 0.5 km to the length that is on the map

[Paul Webster]

There is no definitive answer for this. Your GPS track length will be absolutely accurate in length - if your GPS recorded an absolutely accurate track. Whether it does depends on the quality of your signal, whether it has any 'jitter' etc. SOme GPS are prone to record points whilst they are still getting an accurate fix, which can mean overestimating your distance by quite a margin. Best to look at the track to spot anything like this, then you'll get an idea of the accuracy. On Walkhighlands the figures we give are from GPS tracks which have been 'cleaned' of any errors or jitter.

On the other hand GPS is really not very accurate at all for calculating your altitude, as the satellites are configured to get your lat/long position accurately, but cannot locate an accurate point in the vertical plane (Garmin have an explanation of this in the 2nd paragraph here: https://support.garmin.com/en-GB/?faq=QPc5x3ZFUv1QyoxITW2vZ6 - stating GPS height fixes can be anything upto 400 feet or so out; Viewranger have a page about it here: https://support.viewranger.com/index.php?pg=kb.page&id=60).

It's much more accurate to cross-check your accurate gps-positions against the Ordnance Survey digital terrain model (similar to what is used to draw contour lines) and calculate altitude and ascent from that - which is what most GPS software does these days, ignoring the GPS-calculated heights, since the OS digital terrain model is free. It used to be that alot of GPS software did use altitude from your GPS - but that was in the days when the OS terrain model was something that had to be licensed.