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tiompan May 30, 2009 23:42:42
Replying to gjrk

gjrk wrote:
Bit of a layman's maths crisis. I wonder if you can help, George?

I'm writing something up at the moment and was going to use an example of three sites lining up across the countryside. Obviously, there's quite a good chance that three points can coincide fortuitously, particularly if there's a lot of them around. I'm not claiming that it's deliberate, just that it's there.

I've identified a number of lines by using the utility at:

http://www.iol.ie/~geniet/eng/azimuth.htm

and each site's coordinates. I established the azimuths and distances between each point and then solved the triangle to find the distance between the respective lines.

With the following, for example:

(a) N51.64614, W-9.06488
(b) N51.64749, W-9.00848
(c) N51.64805, W-8.98150

I calculated a line 'ac', length 5.749km where 'b' is 5.72m from 'ac' (+17.55m to -6.12m for 5m GPS error).

Does this add up, or have I gone wrong anywhere?

Thanks in advance,

Gordon.

Hi Gordon , a quick calc and it looks like the maximum "error " is 26 metres over the 5.7 Km distance , there are no rules so it's up to you as to how "straight " you consider that is . The gps error might be greater so it could actually be slightly better or worse . What are the sites and are they intervisible ? Not far off E-W too .

G gjrk
gjrk May 31, 2009 00:09:50
Replying to tiompan

Thanks for the reply George.

The sites are (a) Maulatanvally circle, (b) Knocks S circle, (c) Knockatlowig row.

The row is east of the hilltop, but if you walk a short distance up and west you can make out Knocks S. Not a hope of seeing Maulatanvally from there, its too far off and behind trees from that angle.

[I've a small bunch of lines identified, unfortunately none intervisible. Only two lines have components, beyond the obvious circle/circle or row/row, that could be counted as similar, one has two points with similar (winter sol) orientation, the other has two points with cupmarks (maybe a third but could be natural). These features, for what its worth, only occur at those sites.

My sample was 28 sites of two or more grouped standing stones, in the Carrigfadda area of west Cork. No line has more than three site points, which, of course, could easily occur randomly. Some sites appear on a couple of lines and one line of three sites also contains the peak of Carrigfadda.]