Surveys without centrelines

[Stelios Zacharias]

Dear Kevin, Wookey and Survex group,

Thanks for your time on this - and thanks for the name of the 
methodology. In Greek it is the method of "Trigonism" (??????????? - the 
focus of the name being on the angles rather than the sides, for some 
reason).

I understand that Trilateration as a method is not supported in Survex 
(and therefore also Therion) - whether it should be or not is your call. 
I can probably handle the trigonometry well enough to get excel to 
output the usual distance/bearing/slope data between the points on the 
edge of the shape and then re-input this into Therion.

Cheers,
Stelios Zacharias
SELAS Caving Club, Greece



On 06/09/2013 15:39, kevin dixon wrote:
> The term for this type of survey is Trilateration.
>
> One problem you will have with this is that where there are only two 
> distances to a point, there will be two valid position solutions, 
> equidistant either side of the baseline that has been used to measure 
> from. In this situation, you will need to have some way of telling the 
> algorithm which side of the baseline is correct.
>
> Should this unusual survey method be added to Survex ?
> Would it be better to do the trilateration calculations in excel and 
> then output data suitable for use in Therion/Survex ?
>
> Kevin Dixon
>
> ------------------------------------------------------------------------
> *From:* Wookey <wookey at wookware.org>
> *To:* Survex User Group <survex at survex.com>
> *Cc:* Stelios Zacharias <stelios.zacharias at selas.org>
> *Sent:* Friday, 6 September 2013, 13:20
> *Subject:* Fw: Surveys without centrelines
>
> This was posted to the therion list, but is really a survex question.
>
> > Stelios Zacharias <stelios.zacharias at selas.org 
> <mailto:stelios.zacharias at selas.org>> wrote:
>
> > Can Therion put together scraps on the basis of the polygonal system
> > of survey? (I think this is what it is called - it uses as set of
> > triangles and only distance measurement rather than the distance,
> > azimuth, slope measurements we are used to).
> >
> > A friend has a survey constructed with only distances taken from two
> > points (and successive points) so as to create a flat area of
> > triangles (it is flat because the "floor" is the sea and the water
> > level is constant). There is therefore no centreline, but a series of
> > points, each joined by two measurements to other points and all coming
> > back to a known baseline. In the days of paper survey, the plan would
> > be drawn with just a compass from one point to the next, beginning off
> > the baseline.
>
>
> Survex has a
> *data cylpolar from to tape compass fromdepth todepth
> entry form, which is along the right lines, but that
> still expects bearings and depths.
>
> As Bruce suggests, guessing the bearnings (or putting in arbitrary
> values) and turning the SD up with
> *sd bearing 180 degrees
> might reuslt in the right answer.
>
> Better would be a new input format for this form of data
> *data triangulation from to length fromdepth todepth
> and probably more usefully
> *data triangulation station depth newline tape
>
> I'm not sure how hard it is to add this. (Is it just a new data
> format, or do the solver algorithms have to change?) If the former it
> should be quite straightforward.
>
>
> Wookey
> -- 
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> http://wookware.org/
>
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>
>