Fw: survex questions

[Footleg]

Data from each different date needs to go into a separate begin/end
block. Then inside each block you need to specify the declination
adjustment for the date in question, to convert from whatever North
reference the raw data uses to the north reference you want to use for
the final survey. So if the data is magnetic North on a particular
date then you can set a declination adjustment for that date to adjust
to OS Grid North (assuming this is the grid you are using for your
final survey). The ancient cartesian data is already aligned to true
North, so you just need to set the adjustment to convert it to OS Grid
North from True North.

The question then is whether having data in cartesian format rather
than length,bearing,inclination format will be adjusted by survex when
you apply a declination adjustment to it? After all the data contains
no bearings to apply the adjustment to. If Survex just rotates the
data block by the adjustment factor regardless of the format the data
was entered in then you will be fine. If it does not then you might
need to convert the cartesian data measured off the old printed survey
into length,bearing,inclination format. I have a spreadsheet which can
do that.

Footleg

On 29 June 2012 11:43, Wookey <wookey at wookware.org> wrote:
> ----- Forwarded message from HughStL <hugh at stlawrence.free-online.co.uk> -----
>
> Date: Thu, 28 Jun 2012 11:28:18 +0100
> From: HughStL <hugh at stlawrence.free-online.co.uk>
> To: wookey at aleph1.co.uk
> Subject: survex questions
> X-Spam-Status: No, score=0.1 required=4.5 tests=BAYES_50,RCVD_IN_DNSWL_LOW
>        autolearn=ham version=3.3.1
>
> Hi Wookey, how's things?
>
> Couple of survex questions:
>
> 1. Getting Aygill survey together but have had to create fake
> (cartesian) data for Precambrian from the old 1971 ULSA survey - Pete
> Hall has done this. Only thing is, that old printed survey from which
> Pete has faked his coordinates, has a True North arrow on it. From
> what I can gather from t'internet, the magnetic declination back in
> 1971 was almost 9? West. As the rest of the Aygill survey is based on
> compass magnetic bearings, how do we adjust the Precambrian fake
> survex file to conform with the magnetic norm of the other files?
>
> (there is a whole issue here of mag variations and compass
> calibrations and so on, it's going to be a devil to unravel! Some of
> the survex files go back to the late 80s and I rather suspect some of
> the compass calibrations were just 'borrowed' from some other survex
> file - ie. files copied and name and data changed but not things like
> calibration! Oh shit....)
>
>
> 2. On a more basic understanding level, how should you write a compass
> calibration into a file? For instance, I've just got some suunto
> instruments off ebay - I went to the farm to check the reading against
> the 'calibration test' that's written on the corner of the farm,
> sighting on the signpost. Should be 328? but my compass was 331?.  In
> a survex file, how do you write that compass calibration?  Do you
> write it as +3 (ie. telling survex that the compass reads 3? big). Or
> do you write it as -3, effectively telling survex to subtract 3? from
> all the readings?  I'm not sure how the innards of survex works, and
> therefore what instruction you should be giving it?
>
> Let me know if you need to see any survex file.
>
> By the way, the fake data file (cartesian) screwed up the whole survey
> when it was included in the aygill master - it wouldn't produce a 3d
> and gave loads of errors ('giving up, too many errors'). The solution,
> after much trial and error, was to throw out all the 'export' stuff.
> Then it worked fine!
>
> cheers
> Hugh
>
>
>
> ----- End forwarded message -----
> Wookey
> --
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> http://wookware.org/
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