# calculating gradient on google earth



## fouadaswad

hello all

Any thoughts on calculating slope gradient using google earth? is there a feature that does it automatically? or do i need to do the calculation?

How do all of you out there establish the gradient of hills that you regularly ride? (no altimenter).

thanks all


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## Argentius

Google earth works pretty well, but you've got to do the math.

Find at least a couple hills in your area with highway dept. posted grades. RIde 'em, then compare others to those. At least, that's what I do. I've found posted 6%, 9%, 10%, 12%, 16%, and "21% GRADE AHEAD! TRUCKS USE LOWER GEAR! COMPRESSION BRAKES PERMITTED NEXT 3/4 MILE! USE CAUTION!"


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## DH001

I use GE and Excel to plot elevation profiles for some of my rides, but it is a little tedious. I have included a template if anyone wants to try it out. Instructions below:

The first step is to select the measuring tool under the "Tools" menu in GE. Then start plotting points and entering the cumulative distance into the "Distance" column of the spreadsheet. I usually use .05 km intervals for a "high resolution" profile, but any value can be used. After the points are plotted, mouse over them and input the corresponding elevation displayed in GE into the "Elevation" column. When you are finished, it should spit out the color coded % grade (yellow=mild, orange=hard, and red=very hard), total elevation gained or lost, and a chart representing the terrain.


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## fouadaswad

Thats Great. Thanks


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## Einstruzende

If you want to spend about $65, buy Topo USA. You can create a route (essentially plotted points), and it will tell you the grade % and total elevation gain.


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## PJay

*http://www.gmap-pedometer.com/*

I have used this website to look at elevation changes.

http://www.gmap-pedometer.com/

You use the "elevation" feature, which shows an exaggerated profile, and gives the elevation above sea level in feet.

You have to get really close in, and enter many markers along a segment. It will plot the elevation change from one point to the next.

Then, look at elevation change in feet, on the x axis, compared to distance. You have to convert miles to feet, then do "rise over run."

You can't just look at the profile for peaks and valleys, cuz it keeps resetting the x axis to accomodate the total profile (3 gentle rollers in a row could have the same profile as 3 hors categorie in a row).

The good thing is that this is free, and not too difficult once you mess around with it a while.

Turn "off" mile markers so they are not obscuring the view.

Elevation changes at a creek or river will often have a bridge spanning the creek or river. If you know the topography well, you can just place a marker at each end of bridge, thus accurately including zero elevation change between the two points.


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## OJack

Am I correct in my thinking that to get your grade, you divide elevation by distance...so, a 300ft climb in one mile would be 300/5280=5.6%...is that correct? Also, to get elevation gain I have used my GPS.


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## Spinnerman

OJack said:


> Am I correct in my thinking that to get your grade, you divide elevation by distance...so, a 300ft climb in one mile would be 300/5280=5.6%...is that correct? Also, to get elevation gain I have used my GPS.


No because you are caluclating hypotenuse over rise. You need to convert to run over rise. Remember the equation from Geometry A2 = B2 + C2 (2 meaning squared). You have the infromation for A distance traveled on the climb and C the elevation gained. Now you need to find B = square root of (a2 - c2) then divide C by B to get the grade.


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## Einstruzende

OJack said:


> Am I correct in my thinking that to get your grade, you divide elevation by distance...so, a 300ft climb in one mile would be 300/5280=5.6%...is that correct? Also, to get elevation gain I have used my GPS.


Yes, though technically you use linear distance not terrain distance. For all but really long climbs it's a wash though.


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## BenWA

OJack: that is correct, rise/run=%gradient

fouadaswad: something like TopoUSA is probably your best bet for a quick, albeit low-resolution elevation profile with gradients. 

If you want to know the precise gradient of specific hills you could go to your local hardware or surveying supply store and buy a cheapo clinometer for ~$20 (or if you own a compass, many have built-in clinometers)


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## danl1

Spinnerman said:


> No because you are caluclating hypotenuse over rise. You need to convert to run over rise. Remember the equation from Geometry A2 = B2 + C2 (2 meaning squared). You have the infromation for A distance traveled on the climb and C the elevation gained. Now you need to find B = square root of (a2 - c2) then divide C by B to get the grade.


It would depend in part on whether the mile was measured rolling on the bike, in which case spinnerman is correct, or measured off of a map/gps, where your math is correct.

Not that it matters much for the units we use.

300/5280 = 5.68%
(5280^2-300^2)^.5 = 5271.47
300/5271.47=5.69%


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## cityeast

If you have a Polar 625x/725x/720i, etc , Polar Performance software will calculate the average grades for you between the waypoints (laps) you mark as you go along. Still not completely accurate, but close enough. Naturally the longer the distance between waypoints, the more accurate the average grade reading will be.


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## YandaMan

Try http://www.bikeroutetoaster.com/.

You can map any points using a google maps interface and if you go to the summary it will show you the ascent and descent, max and min, elevation, and distance. So, if you pick a short route on the map (i.e. just your hill), it should give you the distance and total ascent. You'll still need to do the pythagoras stuff, but at least you've got the numbers right there for you.


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## MerlinAma

Talk about reviving and old thread.

5-13-06 to 4-4-09

Wow.


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