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Re: [prominence] Significant saddles

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  • David Metzler
    ... As Roy points out, one way to measure the significance of a saddle is to measure the prominence of the peak for which it is the key saddle (this is
    Message 1 of 3 , Jan 4, 2003
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      >(Andy)
      >>>There are low point baggers and beach baggers (if you want to
      >>>count beach hikes of CA, OR, etc), but few "saddle baggers" to date.
      >
      >(Bob Martin)
      >This is certainly true in AZ but not so in CO. The difference is probably
      >mostly due to the difference in topography.
      >CO high passes have great historical significance. Some are accessible by
      >vehicle, but most make good long hikes. There are several books on the
      >subject.
      >
      >(Roy Schweiker)
      >There were several examples of saddle bagging in the old cohp mailing
      >list. Does a saddle have un-prominence, i.e. the prominence of the peak
      >for which it is the key saddle?

      As Roy points out, one way to measure the "significance"
      of a saddle is to measure the prominence of the peak
      for which it is the key saddle (this is well-defined).
      People on this list have accumulated a wealth of such saddles
      as a by-product of prominence work.

      However I would claim this is a somewhat strange way to measure
      the significance of a saddle/pass, given how a pass is usually used,
      namely, to get from one drainage basin to another. This has nothing
      directly to do with the height of the highest peaks, which is
      measured by the prominence.

      Instead, you want some idea of how likely you are to choose that saddle
      as your method of travel over competing saddles.

      I would like to see a measure of significance which accounts for
      three aspects in which a saddle can be significant:

      (1) it is low;
      (2) it is on a "major" divide;
      (3) it is far away from a "better" saddle.

      Suggestions?

      Dave M.
    • Edward "7.389056099" Earl
      ... In the course of my work, I have occasionally found it quite useful to consider prominence as an attribute of a saddle, where the prominence of a saddle is
      Message 2 of 3 , Jan 4, 2003
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        > As Roy points out, one way to measure the "significance"
        > of a saddle is to measure the prominence of the peak
        > for which it is the key saddle (this is well-defined).
        > People on this list have accumulated a wealth of such saddles
        > as a by-product of prominence work.
        >
        > However I would claim this is a somewhat strange way to measure
        > the significance of a saddle/pass, given how a pass is usually used,
        > namely, to get from one drainage basin to another. This has nothing
        > directly to do with the height of the highest peaks, which is
        > measured by the prominence.
        >
        > Instead, you want some idea of how likely you are to choose that saddle
        > as your method of travel over competing saddles.
        >
        > I would like to see a measure of significance which accounts for
        > three aspects in which a saddle can be significant:
        >
        > (1) it is low;
        > (2) it is on a "major" divide;
        > (3) it is far away from a "better" saddle.
        >
        > Suggestions?

        In the course of my work, I have occasionally found it quite useful to consider
        prominence as an attribute of a saddle, where the prominence of a saddle is
        simply that of the peak of which it is the key saddle. Defined this way, the
        prominence of a saddle is simply its "depth" below the high point of the ridge
        on either side of it, without having to dip below the level of saddle itself.
        In fact, one former widely used name for prominence is a German word that
        translates to English as "notch depth" (I forget the word; Eberhard, can you
        help out here?).

        This way of defining the prominence of a saddle accords with items (1) and (3)
        above which Dave suggests are desirable characteristics of a saddle measure.
        It certainly favors the lowest of a succession of saddles on a divide. If
        you're looking for the lowest pass between two main peaks, it'll be the one
        with the greatest prominence.

        For example, if you are thinking about building a highway through a 2000'
        prominence saddle, it means that you will have to go around the other side of a
        peak that's at least 2000' higher in order to find a lower saddle. Low-prom
        saddles, of the other hand, are close to a lower one on the same ridge; a
        saddle with 100' prominence is going to be very significant.

        Concerning Dave's item (2) above, that depends. Some very high passes on major
        divides have minimal prominence, because there simply isn't much available rise
        on both sides since you're starting very high to begin with. Some continuously
        high ranges, such as the Rockies or Sierras, have a number of famous passes
        that have low prominence for this reason.

        As a leading developer of computational tools for prominence, I occasionally
        find it so useful to define the prominence of a saddle this way that I have
        implemenented in Winprom the capability of calculating saddle prominence and
        preparing lists of saddles by prominence, irrespective of their corresponding
        peaks. Measuring saddle prominence is an important part of several other
        algorithms I have developed that produce useful results, such as identifying
        basin saddles for their potential errors to affect the prominence of peaks, or
        deciding how to correlate saddles between results that were derived from
        different elevation maps.

        Edward "7.389056099" Earl
        esquared@...
        http://www.k-online.com/~esquared/eae.htm
      • Roy Schweiker
        ... other ... saddle. Of course, whether a saddle is heavily used depends on several things: 1) Political boundaries, that is probably why Pinkham Notch (NH
        Message 3 of 3 , Jan 5, 2003
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          > If you're looking for the lowest pass between two main peaks, it'll be
          >the one with the greatest prominence.
          >
          >For example, if you are thinking about building a highway through a
          >2000' prominence saddle, it means that you will have to go around the
          other
          >side of a peak that's at least 2000' higher in order to find a lower
          saddle.

          Of course, whether a saddle is heavily used depends on several things:
          1) Political boundaries, that is probably why Pinkham Notch (NH 16) is a
          major thoroughfare while lower Evans Notch (NH/ME 113) isn't even plowed
          in winter because they chose to build entirely within a state
          2) Ease of construction, the heavily-traveled US 4 in VT crosses
          Sherburne Pass (2150', -658' prominence) while Elbow Road (requires jeep)
          uses the key saddle (1951', -2290' prominence)

          Note that US 6 in CA apparently used different locations over time
          according to the page Andy found

          >As a leading developer of computational tools for prominence,

          Hmm, not the sort of expert you can look up in the phone book :-)

          -rs



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