[Manifold-l] Distance calculations

[Linus F Upson III]

    Very simply, for purposes of reporting the factual data  (e.g.: this 
happened at this time and at this point or at this direction from this 
point) then all that data acquisition and reporting was done in lat/lon to 
everybody all at once.  But analysis is very different.  There are other 
data sets which need to be added and may cause projecting the raw data. 
Sometimes great circle routes need to be plotted and displayed.  Some 
reports must be done in metric units.  Some software requires that spatial 
inputs be in a certain projection for a certain part of the world.  Some 
researchers are more comfortable working in one projection (or none) than 
others.  And so forth.  Hence the analytic and reporting functions can be 
addressed in extremely different ways.
    To get back to the original message.  I feel your pain and I think that 
a common set of distances, radians, degrees, should be accessible from a 
single radio button between any two points in a drawing.  As I think 
buffers, relates, areas etc., should also be that "simple" to show.  But 
there would be a lot of science behind that button.  Linus


----- Original Message ----- 
From: <david at jodael.com>
To: <manifold-l at lists.directionsmag.com>
Sent: Friday, 22 September, 2006 8:56 PM
Subject: RE: [Manifold-l] Distance calculations


> On 22 Sep 2006 at 12:07, Dimitri Rotow <dar at manifold.net> wrote:
>
>> To date the Manifold approach has been to have faith that beginners could 
>> be
>> taught the necessary ideas.  It's not that much of a stretch to tell 
>> people
>> that if they are measuring distances they should be doing that in a
>> projection, not lat/long, and then those people who need to make 
>> precision
>> comparisons will be led (one hopes) into delving deeper into the details.
>
> The problem here is that if you are a new user who wants to get a cheap 
> solution to
> plot your GPS tracks, you aren't going to understand projections & datums 
> & are just
> going to wonder why Manifold can't measure distances in metres, while your 
> trusty
> GPS can.
>
> And if it is someone coming down from higher-end packages like MapInfo you 
> are
> going to wonder about the same thing - MapInfo allows distance 
> measurements in
> metres if working in WGS-84. Presumably ESRI products do also? (I have 
> never used
> ESRI)
>
> One day everything we own will have a GPS in it - our phones, our cameras, 
> our cars
> and probably our watches. WGS-84 is the defacto standard for GPS 
> positioning, but if I
> show an average user that the distance between point A & point B is 
> 0.12345 degrees,
> all I will get is a blank look. It still seems unnecessary to me that when 
> I have maps in
> WGS-84 & data (from GPS) in WGS-84 that I would have to jump through hoops 
> to
> get distances measured in a form that an average user of my application 
> would
> understand. And yes, I do work for a hydrographic survey company & have 
> people with
> double degrees in maths & surveying on staff who spend half their lives 
> delving into the
> intricacies of Timbalai 1948 & Kertau & Indian feet, etc. Still, most of 
> our work these
> days is entirely in WGS-84 the single biggest question that any end user 
> wants
> answered is "how far am I from object X?". All subsequent questions derive 
> from that -
> i.e. "how long is it going to take me get there?", or "what area did I 
> cover in my
> travels?". I can go on all day with my customers about projections, but at 
> the end of
> that day he is still going to want to know how many metres or nautical 
> miles he is away
> from another object and he could be anywhere in the world (our customers 
> stretch
> from Japan to West Africa) and all he has in the way of data is 
> GPS-derived target info
> & their own GPS positions.
>
> Linus -  I was interested in your comment "it quickly became apparent that
> lat/lon WGS84 was THE shared approach.  Then, when analysis started, 
> ...". Going to
> elaborate? :-) I'm quite interested in the problem faced & the best 
> solution.
>
> Dave
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