Thank you for your kind remarks. Wish that were so, but as many of
my archaeological friends will tell you I have no concept of spatial
relationships, let alone theodolite surveying which has always been a
mystery to me.
Do they set the theodolite to a specific point, degree, whatever and
draw those straight lines in sections moving from one viewable point to
next using the same setting each time? I notice there always has to be
someone at the other end of the line to set the marker.
Its probably a dumb question anyway! Thanks for trying to explain.
On 3/30/01 11:51 PM Andrew Smith writes:
>In practice, to all intents and purposes in most terrain other than wide
>open plains etc the radius of the earth is so large in comparison to the
>distance one can see that the "arc"on the surface (even assuming the earth's
>surface was smooth) is seen to all intents and purposes as a straight line.
>Anyway, if one is surveying one is measuring in straight lines anyway
>("Lines of sight") almost by definition. (That is unless we get really
>esoteric and wonder about atmospheric refraction or whether the earth's
>gravitational field has a measurable effect on light, but let's stay
>In effect, if one draws a sufficiently large number of sufficiently short
>lines at rightangles to a series of large radii the resultant polyhedron
>will eventually approximate to a circle for all practical purposes.
>If on a spherical body the sectional view would be an arc, but the plan view
>would still be a straight line, cf "great circle" routes for aircraft.
>Sorry, I'm an engineer who has been recycled as an archaeologist! You
>probably had this sussed all along and just had your tongue in your cheek.
>----- Original Message -----
>From: "Bea Hopkinson" <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Saturday, March 31, 2001 2:29 AM
>Subject: Re: Roman Roads, a query
>> Now wait a minute, to be even pendantic, we are talking Roman here and
>> they still held the peripetatic and flat earth view, so they wouldn't
>> be thinking in arc's. But i guess what you are saying Mark is that
>> whether they liked it or not their straight line became arc'd. Somehow
>> can't envisage how that would work out in practice?
>> On 3/30/01 2:41 AM John Wood writes:
>> >>>> Mark Bell <[log in to unmask]> 03/30 9:41 am >>>
>> >To be absolutely pedantic the shortest distance between two points on the
>> >Earth's surface is an arc (a section of a circle).
>> >Any "straight" line drawn on a map is actually a curve. This is one of
>> >best arguments against the existence of lay lines!
>> Beatrice Hopkinson 73071,327@compuserve
Beatrice Hopkinson 73071,327@compuserve