Determining Steepness of Grade

Discussion in 'Recumbent bicycles' started by Vol, Jun 15, 2003.

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  1. Vol

    Vol Guest

    In various threads here, posters refer to steepness of a grade in terms of percentage.

    The math is simple: elevation change divided by distance traveled times 100 yields
    percentage of grade.

    I find myself wondering, though, how various posters obtain the elevation change data.

    If anyone feels like providing some education, I'm ready to learn. It would be mildly interesting to
    know if that knee-burner is a big nasty seven or more like a four.

    George
     
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  2. Brian Hughes

    Brian Hughes Guest

    > I find myself wondering, though, how various posters obtain the elevation change data.
    >

    I use a Garmin GPS and take the elevation reading from it. Although a GPS elevation reading itself
    isn't exact, they're plenty good enough to note the elevation at the top of a hill and subtract the
    elevation at the bottom and that value is the hill's elevation change. I've found that if I do this
    on different days, my GPS elevation reading at the top and bottom of a hill may vary a bit--but
    when you subtract the difference between them (the elevation change), it is pretty much
    consistently the same.

    In other words, if you take a GPS elevation reading for the top of a hill, also take the elevation
    reading for the bottom of the hill right away. Don't take the second reading on a different day.

    Brian Tailwind/V-Rex
     
  3. Ben

    Ben New Member

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  4. I use "Topo-USA" Delorme's map program, it calculates %grade for me. It will also tell me the
    elevations at any point in a route, so I could calculate it myself.

    --
    Gene O _ \ _/\,%) (*)--(*)

    [email protected] http://home.att.net/~gene8

    "Vol" <[email protected]> wrote in message news:[email protected]...
    > In various threads here, posters refer to steepness of a grade in terms of percentage.
    >
    > The math is simple: elevation change divided by distance traveled times 100 yields percentage
    > of grade.
    >
    > I find myself wondering, though, how various posters obtain the elevation change data.
    >
    > If anyone feels like providing some education, I'm ready to learn. It would be mildly interesting
    > to know if that knee-burner is a big nasty seven or more like a four.
    >
    > George
     
  5. Cletus Lee

    Cletus Lee Guest

    In article <[email protected]>,
    [email protected] says...
    > I use "Topo-USA" Delorme's map program, it calculates %grade for me. It will also tell me the
    > elevations at any point in a route, so I could calculate it myself.

    TopoUSA only reports what it can measure from the data (topo contours and road position). Usually
    both are very wrong. Road cuts and fills (used to level out the road)usually do not warrant a shift
    in contour lines and are invisible to TopoUSA.

    Most GPS have a vertical accuracy of +/- 10-20m So using the relative difference on elevation as
    some have mentioned may or may not always work either.

    At best you will only get an approximation.
    >
    >

    --

    Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
    - Bellaire, TX USA -
     
  6. "Cletus Lee" <[email protected]> wrote in message news:[email protected]...
    > In article <[email protected]>,
    > [email protected] says...

    > Most GPS have a vertical accuracy of +/- 10-20m So using the relative
    difference on elevation
    > as some have mentioned may or may not always work either.
    >
    > At best you will only get an approximation.

    In open country, where the signal from a couple of low-elevation satellites is strong, the GPS
    altitude measurements can get to be quite good on my Garmin. They compare well with posted
    elevations at divides for example, and some differential measurements I've taken under the same
    conditions correspond well with the gross topo differentials.

    As a general rule, though, GPS altitudes and earth's surface can't be trusted.

    Fred Klingener
     
  7. Bandjhughes

    Bandjhughes Guest

    "Fred Klingener" <[email protected]> wrote in message
    news:<[email protected]>...
    > "Cletus Lee" <[email protected]> wrote in message
    > news:[email protected]...
    > > In article <[email protected]>, [email protected]
    > > says...
    >
    > > Most GPS have a vertical accuracy of +/- 10-20m So using the relative
    > difference on elevation
    > > as some have mentioned may or may not always work either.
    > >
    > > At best you will only get an approximation.
    >
    > In open country, where the signal from a couple of low-elevation satellites is strong, the GPS
    > altitude measurements can get to be quite good on my Garmin. They compare well with posted
    > elevations at divides for example, and some differential measurements I've taken under the same
    > conditions correspond well with the gross topo differentials.
    >
    > As a general rule, though, GPS altitudes and earth's surface can't be trusted.
    >
    > Fred Klingener

    In my experience, the differential measurement is consistently quite good. More so than the absolute
    elevation. In other words, noting the elevation change between point A and point B will almost
    always give the same result on on any given day even though the absolute elevation reading at point
    A and point B may be different by 30 feet or more on different days.

    For example, if today's elevation reading is 30 feet higher at the top of a hill than yesterday's
    reading, it will also (most likely) be about 30 feet higher on the bottom of the hill too. So
    when you subtract the difference to calculate the height of the hill--the result will be very
    near the same.

    Brian
     
  8. The precision of GPS units will be somewhat dependent on the type of units used. I have purchased
    several of the Garmin hand held units for our Survey group. I have tested them against points of
    known elevation. During a five minute episode I have seen them vary as much as 20 to 30 ft on both
    sides of the published elevation.

    I also have GPS units which are capable of accuracy in the centimeter range (dependent upon the
    network we use.)

    A 30' error in a mile will be about 0.5% which is probably no big deal. A 30" error in 500' is
    a 6% error.

    As long as you use caution and common sense I would think that the GPS derived elevations would
    yield acceptable results.

    William L. Higley, Sr., P.L.S. Vision R-50

    "bandjhughes" <[email protected]> wrote in message
    news:[email protected]...
    > "Fred Klingener" <[email protected]> wrote in message
    news:<[email protected]>...
    > > "Cletus Lee" <[email protected]> wrote in message
    > > news:[email protected]...
    > > > In article <[email protected]>,
    > > > [email protected] says...
    > >
    > > > Most GPS have a vertical accuracy of +/- 10-20m So using the relative
    > > difference on elevation
    > > > as some have mentioned may or may not always work either.
    > > >
    > > > At best you will only get an approximation.
    > >
    > > In open country, where the signal from a couple of low-elevation
    satellites
    > > is strong, the GPS altitude measurements can get to be quite good on my Garmin. They compare
    > > well with posted elevations at divides for
    example,
    > > and some differential measurements I've taken under the same conditions correspond well with the
    > > gross topo differentials.
    > >
    > > As a general rule, though, GPS altitudes and earth's surface can't be trusted.
    > >
    > > Fred Klingener
    >
    > In my experience, the differential measurement is consistently quite good. More so than the
    > absolute elevation. In other words, noting the elevation change between point A and point B will
    > almost always give the same result on on any given day even though the absolute elevation reading
    > at point A and point B may be different by 30 feet or more on different days.
    >
    > For example, if today's elevation reading is 30 feet higher at the top of a hill than yesterday's
    > reading, it will also (most likely) be about 30 feet higher on the bottom of the hill too. So
    > when you subtract the difference to calculate the height of the hill--the result will be very
    > near the same.
    >
    > Brian
     
  9. I don't know what you're talking about. Topo-USA works in 1' increments and has nothing to do with
    contour lines when calculating elevation. When calculating the grade of a hill, you can measure the
    elevation at the bottom and the elevation at the top, all within 1 foot, then measure the distance
    to calculate %grade. I've found Topo to be very accurate especially compared to GPS and cycle
    altimeters. When Topo gives an altitude of a point it compares exactly to all references I can find,
    which is far more than I can say for any consumer GPS I've seen. The references to which I refer are
    official altitude markers at passes also, since I'm a pilot, I have charts for airport elevations
    and Topo agrees exactly with those. I've seen GPS units vary by 50 feet in a few minutes without
    moving an inch. That goes for both Magellan and Garmin. What evidence do you have for the inaccuracy
    of Topo? I will agree that road position for very short and curvy sections are not especially
    accurate in Topo, but for the length of the hill from bottom to top the total elevation gained, and
    that's what is important in this calculation, it is extremely accurate.

    Gene

    "Cletus Lee" <[email protected]> wrote in message news:[email protected]...
    > In article <[email protected]>,
    > [email protected] says...
    > > I use "Topo-USA" Delorme's map program, it calculates %grade for me. It will also tell me the
    > > elevations at any point in a route, so I could calculate it myself.
    >
    > TopoUSA only reports what it can measure from the data (topo contours and
    road position).
    > Usually both are very wrong. Road cuts and fills (used to level out the
    road)usually do not
    > warrant a shift in contour lines and are invisible to TopoUSA.
    >
    > Most GPS have a vertical accuracy of +/- 10-20m So using the relative
    difference on elevation
    > as some have mentioned may or may not always work either.
    >
    > At best you will only get an approximation.
    > >
    > >
    >
    > --
    >
    > Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
    > - Bellaire, TX USA -
     
  10. Cletus Lee

    Cletus Lee Guest

    How about the roads near N37° 23.235' W80° 23.584' and N37° 21.247' W80° 32.022' First, the roads
    are not where the map says they are and this may be its biggest problem. Second, none of the cuts
    and fills are expressed in the topography or the underlying data points. I believe the contour lines
    are derived by TopoUSA from selected input points (which are not necessarily closely spaced or even
    in a uniform grid.)

    Since you are a pilot, I think you should get out of the clouds and get your feet on the ground.
    Remember that those airport elevations that TopoUSA agrees with are flat places and near known
    input points.

    I have written computer contouring mapping programs and have spent the last 40 years intimately
    acquainted with geological and topographical maps. I think the most accurate (in the US) topo maps
    are those published by the USGS. They are only accurate at the surveyed Bench Marks. Even these are
    sometimes in error. And especially those in remote mountainous areas where these grades are being
    determined. Everything on a USGS topo map between Bench Marks are guesses. The guesses may be based
    upon stereo photographic information and made by a computer, but they are still guesses. The closer
    a point is to a BM, the more accurate it tends to be. I believe TopoUSA uses a similar photographic
    method to suppliment known points.

    As for GPS. I registered my GPS two days earlier at a USGS BM about 40 miles from the point where
    this picture was taken. http://www.clee.org/MoM2002/image029.htm
    http://www.clee.org/MoM2002/image030.htm

    The Blueridge Parkway sign called the elevation of the overlook 2400' the GPS registered 2370' the
    Topo map in the GPS memory (Not TopoUSA) said that I was on the 2100' contour. The location of the
    GPS in relation to the road on the map said that I was about 50' NW of the BRP. IIRC, the data
    point from the GPS when plotted on TopoUSA was about as inaccurate as the topo data in the GPS. I
    will try to find the track for that trip and give you the coordinates for that point so you can
    compare for yourself.

    BTW, TopoUSA (v4.0) is a fine product as long as you consider it's limitations. Here are some
    impressive jpegs of the kind of things that TopoUSA can do well.

    http://www.clee.org/BikeTrips/default.cfm?main=MoM.cfm Click on each one to enlarge.

    You also may be interested in this review of TopoUSA 4.0 by Alex Wetmore:
    http://phred.org/~alex/bikes/topo4.html

    In article <[email protected]>,
    [email protected] says...
    > I don't know what you're talking about. Topo-USA works in 1' increments and has nothing to do with
    > contour lines when calculating elevation. When calculating the grade of a hill, you can measure
    > the elevation at the bottom and the elevation at the top, all within 1 foot, then measure the
    > distance to calculate %grade. I've found Topo to be very accurate especially compared to GPS and
    > cycle altimeters. When Topo gives an altitude of a point it compares exactly to all references I
    > can find, which is far more than I can say for any consumer GPS I've seen. The references to which
    > I refer are official altitude markers at passes also, since I'm a pilot, I have charts for airport
    > elevations and Topo agrees exactly with those. I've seen GPS units vary by 50 feet in a few
    > minutes without moving an inch. That goes for both Magellan and Garmin. What evidence do you have
    > for the inaccuracy of Topo? I will agree that road position for very short and curvy sections are
    > not especially accurate in Topo, but for the length of the hill from bottom to top the total
    > elevation gained, and that's what is important in this calculation, it is extremely accurate.
    >
    > Gene
    >
    > "Cletus Lee" <[email protected]> wrote in message
    > news:[email protected]...
    > > In article <[email protected]>, [email protected]
    > > says...
    > > > I use "Topo-USA" Delorme's map program, it calculates %grade for me. It will also tell me the
    > > > elevations at any point in a route, so I could calculate it myself.
    > >
    > > TopoUSA only reports what it can measure from the data (topo contours and
    > road position).
    > > Usually both are very wrong. Road cuts and fills (used to level out the
    > road)usually do not
    > > warrant a shift in contour lines and are invisible to TopoUSA.
    > >
    > > Most GPS have a vertical accuracy of +/- 10-20m So using the relative
    > difference on elevation
    > > as some have mentioned may or may not always work either.
    > >
    > > At best you will only get an approximation.
    > > >
    > > >
    > >
    > > --
    > >
    > > Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
    > > - Bellaire, TX USA -
    >
    >

    --

    Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
    - Bellaire, TX USA -
     
  11. Mike

    Mike Guest

    is there a difference between steepness of grade and elevation gain? i could see topo being accurate
    for elevation gain calculations . however i dont belive the roads that are drawn on the map are
    accurate enough for measuring the grade. inaccurate placement of road details woulr alter the grade.
    i find the garmin legend GPS accurate for elevation if the sateelitte reception is over 5sat . i
    find it than matches or could be more accurate than topo maps. however if the reception is poor or
    minimAL 3 SAT the elevation could be off a while lot, much more than 500feet even though the margin
    of error on th gps is showing 150 foot circle. i find that the margin of error circle is more
    accurate with horizontal(land). when the gps margin of error circle is under 20 feet i find the
    elevation extremely accurate. i use it to resset my sunnoto altimater
     
  12. Geob

    Geob Guest

    > Topo-USA works in 1' increments and has nothing to do with contour lines when calculating
    > elevation.

    But it does use its own internal digital elevation model. Which is prolly derived from the USGS. And
    doesn't have 1' resolution. They seem to have a good method of interpolating elevations between
    known values though.

    I sometimes use TOPO-USA here at work if I have no other data available for an area. I have checked
    it against my known High Precision Geodetic Network (HPGN) points, and it does seem very good.

    George Bearden Geographic Information System (GIS and Automated Mapping) Group Leader City of Fresno
     
  13. Most climbs or hills are curves in reality and "grade" is accurate only at the point at which the %
    grade is measured. Accurate grades can not be calculated from taking the difference between the
    beginning elevation and the final elevation unless one is measuring a constant grade portion of a
    climb. Using elevations from the bottom and top of a mountain or hill will not give you % grade,
    only change in elevation.

    "mike" <[email protected]> wrote in message
    news:[email protected]...
    > is there a difference between steepness of grade and elevation gain? i could see topo being
    > accurate for elevation gain calculations . however i dont belive the roads that are drawn on the
    > map are accurate enough for measuring the grade. inaccurate placement of road details woulr alter
    > the grade.
     
  14. Brian Hughes

    Brian Hughes Guest

    "Dennis Tresenriter" <[email protected]> wrote in message
    news:[email protected]...
    > Most climbs or hills are curves in reality and "grade" is accurate only at the point at which the
    > % grade is measured. Accurate grades can not be calculated from taking the difference between the
    > beginning elevation and the final elevation unless one is measuring a constant grade portion of a
    > climb. Using elevations
    from
    > the bottom and top of a mountain or hill will not give you % grade, only
    change
    > in elevation.
    >

    Most people want to know the average grade for the hill which can be found by noting the change in
    elevation divided by the horizontal distance traveled (using the same units) x 100. Not to many
    people are interested in the grade at every discrete point. Your argument would mean that even a
    flat and level dry lake bed like the Salt Flats would probably have an extreme grade at some point
    if you happen to ride over a rock.
     
  15. Tom Sherman

    Tom Sherman Guest

    Vol wrote:
    >
    > In various threads here, posters refer to steepness of a grade in terms of percentage.
    >
    > The math is simple: elevation change divided by distance traveled times 100 yields percentage
    > of grade.

    Strictly speaking, percent grade is elevation change divided by the horizontal distance traveled
    multiplied by 100. However, for most real world roadway grades, the distance traveled along the
    roadway is sufficiently close enough to the horizontal component of this distance for the error
    to be small.

    Tom Sherman - Various HPV's Quad Cities USA (Illinois side)
     
  16. Just Zis Guy

    Just Zis Guy Guest

    On Thu, 19 Jun 2003 02:28:15 GMT, "brian hughes" <[email protected]> wrote:

    >Most people want to know the average grade for the hill

    I want to know the maximum grade which is sustained for any distance of more than ten yards or so.

    Guy
    ===
    ** WARNING ** This posting may contain traces of irony. http://www.chapmancentral.com Advance
    notice: ADSL service in process of transfer to a new ISP. Obviously there will be a week of downtime
    between the engineer removing the BT service and the same engineer connecting the same equipment on
    the same line in the same exchange and billing it to the new ISP.
     
  17. "Just zis Guy, you know?" skrev...
    > >Most people want to know the average grade for the hill
    >
    > I want to know the maximum grade which is sustained for any distance of more than ten yards or so.

    I usually just want someone to tell me its gonna end soon (the hill).

    M.
     
  18. Cletus Lee

    Cletus Lee Guest

    In article <[email protected]>, [email protected] says...
    > On Thu, 19 Jun 2003 02:28:15 GMT, "brian hughes" <[email protected]> wrote:
    >
    > >Most people want to know the average grade for the hill
    >
    > I want to know the maximum grade which is sustained for any distance of more than ten yards or so.

    If that is the case, the number you are looking for will not be accurately determinable from a topo
    map or topographic software.

    Though forshortened by the camera, this hairpin turn is close to 20°(36%) at the switchback. The 2
    1/2 mile Category 2 climb from the valley to the top rises ~1100' or 8% grade.

    http://www.clee.org/MoM2002/image022.htm

    Do you really want to know??? Which is more difficult? the 2 1/2 miles or this 10m section? I can
    climb this 10m section. I could not do it after the previous 2 miles or the 67 miles of climbing
    that preceeded that.

    --

    Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
    - Bellaire, TX USA -
     
  19. Just Zis Guy

    Just Zis Guy Guest

    On Thu, 19 Jun 2003 07:29:44 -0500, Cletus Lee <[email protected]> wrote:

    >Which is more difficult? the 2 1/2 miles or this 10m section?

    If I know about the 10m section I can fit the lower geared cassette ;-)

    But I know what you mean.

    Guy
    ===
    ** WARNING ** This posting may contain traces of irony. http://www.chapmancentral.com Advance
    notice: ADSL service in process of transfer to a new ISP. Obviously there will be a week of downtime
    between the engineer removing the BT service and the same engineer connecting the same equipment on
    the same line in the same exchange and billing it to the new ISP.
     
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