Measuring Grade

[sandiegoland 0]

Grade is not an angular measurement. Grade is a percentage of change in elevation over distance. You take the "rise" or elevation change and divide it by the "run" or horizontal distance traveled, then times that number by 100 to get percent. It is important to note that the "run" is not wheel or travel distance as recorded by an odometer, though for most slopes that number will be close.

If the elevation change is 200 feet after traversing 1000 feet horizontally, then:

(200/1000)*100 = 20% grade

If you care, that is also an 11 degree angle: INVTAN(200/1000) = 11.31

1. Open Mapsource

2. Upload Tracks from the GPS device

3. Save the file.

4. Save the file as a new name you can edit.

5. If multiple tracks, identify the track with the section you wish to determine the grade.

6. For ease, delete the track points before and after the section you wish to determine, leaving 5 to 10 points before and after. If you went up and down leave all that data in. It will give you a chance to measure the slope several times (the more readings the more accurate).

7. In the track dialog box, click "Show Profile..."

8. Check the "Show Track Points" box to see how many points are measuring the slope.

9. Select the "Red Marker Tool" and place it at the bottom of the slope.

10. Select the "Blue Marker Tool" and place it at the top of the slope. You now have enough data to make the calculation of grade.

(note there is vertical exaggeration when you view the profile in Mapsource. Do not attempt to "measure" it on your screen with a scale/ruler. Use the figures Mapsource displays.)

(78/269)*100 = 29% grade

Note that individually the track points are not accurate. If you have a very short slope you will not get an accurate grade calculation. Further you are really measuring the overall grade of the steepest section from bottom to top -- there could easily be brief sections within a dirt grade that are steeper. Measuring the decsent of this slope, and additionally measuring what appeared to be the steepest section at the top of the acsent yielded results that varied between a 25% and 35% grade.

[paulmbowers 236]

Pfft. Duh.

[sandiegoland 0]

Pfft. Duh.

[2Wheels 0]

Thanks for a very nice tutorial! I didn't know about that feature of Mapsource.

[sandiegoland 0]

Thanks for a very nice tutorial! I didn't know about that feature of Mapsource.

It's most useful for hiking and biking, trivial fun when you are on a motor... though I did use it to calculate a particular grade on my rally in case anyone had limit to what they wanted to do with street tires.