how to calculate average gradient of a hill

feck sake lads

thebourke wrote: »

I want to calculate a hill i recently cycled....how do i work out the gradient for it?I have standard cateye micro wirless comput but it doesn't have a gradient feature on it...can some recommend a wireless computer with a gradient feature that is not too expensive?

there you go.

CillianL

Gradient is the distance traveled on the slope divided by the height so therefore if you travel 100m and gain 1m then the gradient is 1%.

Also trigonometry helps.
sine(angle of slope)= height/horizontal distance

smacl

CillianL wrote: »

Gradient is the distance traveled on the slope divided by the height so therefore if you travel 100m and gain 1m then the gradient is 1%.

Also trigonometry helps.
sine(angle of slope)= height/horizontal distance

Nope, gradient is the distance you travel in plan over the height you gain. See http://www.mathsisfun.com/gradient.html

feck sake lads

Just buy that gizmo for feck sake:D:D

manwithaplan

smacl wrote: »

http://www.mathsisfun.com/gradient.html

If you have to be told that something "is fun", it most probably isn't.

Nonetheless, that's kind of important about progress being "in plan". Do gps yokes give you your progress in plan whereas yokes calculating wheel revolutions give you a measurement along the jaggedy line of the earth's surface?

Lumen

manwithaplan wrote: »

If you have to be told that something "is fun", it most probably isn't.

Nonetheless, that's kind of important about progress being "in plan"

I take your "not fun" and raise it to the power of "not important".

smacl

manwithaplan wrote: »

Do gps yokes give you your progress in plan whereas yokes calculating wheel revolutions give you a measurement along the jaggedy line of the earth's surface?

Yep, though you need to be hitting some serious hills for it to be a cause for concern. Also, rumour has it that the world is not flat as previously thought, which can lead to yet more complication.

smacl

Lumen wrote: »

I take your "not fun" and raise it to the power of "not important".

I'll need to call on someone from the labs to explain that one to me

sy

smacl wrote: »

Nope, gradient is the distance you travel in plan over the height you gain. See http://www.mathsisfun.com/gradient.html

under

Lumen

smacl wrote: »

I'll need to call on someone from the labs to explain that one to me

Source: me

Sundy

smacl wrote: »

Way easier and more accurate to scale height differences of a map or terrain model.

Are you saying its more accurate and easier to scale the altitude change off a map rather than use a GPS unit like a Garmin 500?

Im not so sure really, the mark on a ruler that your would use to measure the distance would represent anywhere from 2 to 20 metres depending what scale map you are using.
The contour lines them selves are also going to represent a line on the ground of a similar width.

When you pull all those errors together I think the GPS would win every time.

smacl

Sundy wrote: »

Are you saying its more accurate and easier to scale the altitude change off a map rather than use a GPS unit like a Garmin 500?

Depends very much on the distances involved, the type of map, the type GPS and corrections used, and the other sources of error at play. For short distances, e.g. 20-30m, or small heigh differences, they'll both be crap. Without decent surveying equipment, I'd say your best bet to measure gradient with the kit you have for shorter distances is to use the magnet and wheel for distances and barometer for height. If you have one of FSLs inclinometers, better still. For height measurement, the quality of the result from the GPS will vary based on satellite availability and geometry, and interference factors such partial blocking of the sky by trees etc... Consumer grade GPS tends to be very poor for height measurement, hence the inclusion of a barometer in the Garmins. The barometer is good for measuring height differences over short periods of times and stable weather conditions, but weaker over long time frames.

a 1:25,000 map will theoretically let you measure plan position to about 2.5m if you can pick a point to the nearest mm, and height to about 5m or half the contour interval. So for a plan distance of say 1km and height difference of 100m, the main part of my error will be height (e.g. 10m in 100m) or 10% as opposed to 5m in 1km or 0.5% for plan. It is also very repeatable, in that different people will get the same results with the same map on different days.

The barometer coupled with plan GPS could well do better on average, but how do we know? Maybe some keen mapping / cycling types can keep GPX files from the same circuit over the course of a year and see how the results pan out.

When you pull all those errors together I think the GPS would win every time.

You could well be right, though I'd be tempted to try and measure this rather than guess it. With that many boardsies uploading Garmin 500 data to strava and the like, I wonder how easy it would be to pull a bunch of files for the same segment and compare them for variance. A quick search on google doesn't show as much contemporary data as I'd expect.

FWIW, chatting to another lad on the WW200 forum showed different measurements for total height ascended ranging from 2511m to 3117 m for the same circuit.

Sundy

Do devices like the Garmin have the ability to receive DGPS corrections? Even then height is still going to be pretty crap.
Best way to measure elevation is level and staff :-)

Theoretically 2 two similar gps devices viewing the same satellites on the same point at the same time should get the same location. do garmins output to csv?

smacl

Sundy wrote: »

Do devices like the Garmin have the ability to receive DGPS corrections?

The receivers can theoretically pick up WAAS and EGNOS corrections but given corrections only went live in June 2011 for Europe, I'm not sure whether they're in common usage.

Even then height is still going to be pretty crap.
Best way to measure elevation is level and staff :-)

Yep, but levelling some of the roads in Wicklow would be a major task. This was the method used to establish the control for most of the older mapping. These days, much easier to borrow a NRTK GPS which will give you about 25mm in 3d for short occupation times.

Theoretically 2 two similar gps devices viewing the same satellites on the same point at the same time should get the same location.

Yes, but the results are prone to vary significantly if taken at different times / conditions.

do garmins output to csv?

Yup, you can get a GPX file out which is ASCII including WGS84 coords. My older 76CS also can output NMEA0183.

Sundy

Are you a surveyor also?

Haha levelling the roads is exactly why I wouldnt like to have lived when the only option available was theodolite.

6 months ago I wouldnt have had to borrow a RTK, I could have just done it at the weekend. But even then lack of repeatability used to nearly make me cry!
I've (thankfully) givin up the field work route :-)

Sundy

Can the Garmin be set to receive the Marine DGPS from the Irish lights? Would improve the plan accuracy somewhat.

smacl

Sundy wrote: »

Are you a surveyor also?

Developing land survey and surface modelling systems for the last 28 years for my sins. Only get out to the field these days for the odd bit of testing, hence getting out on the bike more.

doozerie

Lumen wrote: »

Source: me

Those are interesting slopes/curves, I wonder how you could measure the gradient of them?*

*Welcome to your Groundhog Day thread

Donelson

Could you compare your distance traveled versus you change I'm latitude and longitude, then take the distance traveled as the hypotenuse etc etc etc

manwithaplan

Donelson wrote: »

Could you compare your distance traveled versus you change I'm latitude and longitude, then take the distance traveled as the hypotenuse etc etc etc

If you did a hill running directly from south to north, you would have a gradient of infinity or something. I'm not sure I could manage that, even on 34-27.

smacl

Donelson wrote: »

Could you compare your distance traveled versus you change I'm latitude and longitude, then take the distance traveled as the hypotenuse etc etc etc

Nice idea, but no. What you're talking about here is referred to as the great circle distance and it's relationship to the distance travelled. If you had just one hill from start to finish, this would work, but for multiple hills you don't have enough information.

jinkypolly

Donelson wrote: »

Could you compare your distance traveled versus you change I'm latitude and longitude, then take the distance traveled as the hypotenuse etc etc etc

Yes you could do this to calculate one gradient. Using Pythagoras to get your change in height and then using the lat/long distance to get your gradient.