[Manifold-l] Distance calculations

[david at jodael.com]

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