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<div class="moz-cite-prefix">Hi,<br>
<br>
Ok OIly and Wookey<span id="result_box" class="short_text"
lang="en"><span class="">, you are right, my formula has not
been very lucky. </span></span><span id="result_box" class=""
lang="en"><span class="">It was an attempt to understand what
error he was experiencing when compiling data with fore/back
bearings. </span></span><span id="result_box" class=""
lang="en"><span class="">I found a large difference in loop
closure error between Auriga (2.85 m in 1967m loop), Compass
(2.9m) and Therion (14m).<br>
<br>
Debugging the compilation I have found that the data
transferred to Survex (data.svx), don't have sense to me. I
have searched in the code source and found the complicated
formula. <br>
I made my own formula in a Excell, and calculate the average.
With this I have detected a strong magnetic anomaly in one leg
(Auriga has this bearing manually discarded, and the
translation to Compass was OK, but to Therion the fore-bearing
was translated with a 0, a 56 degrees difference with the
inverse back-bearing). After to correct the magnetic anomaly
and to calculate the fore-bearing with the inverse
back-bearing, the loop error it's OK too in Therion (2.9m).<br>
</span></span><br>
<span id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="" lang="en"><span class="">Only that
it was necessary to understand what numbers Therion was
going through to Survex, and that some degrees were
deviating from those calculated manually. With the two
files attached in the previous message:<br>
-a file with magnetic declination to 0 and fore/back
bearings<br>
-a file with DM=0 and my average bearings.<br>
<br>
I have compared the results, </span></span></span></span><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="short_text" lang="en"><span
class="">that are the same. </span></span></span></span></span></span><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="short_text" lang="en"><span
class=""><span id="result_box" class="" lang="en"><span
class="">After looking carefully at the files and
the compilation log, I found the difference. The
data transferred to Survex are: bearing -
magnetic declination - meridian convergence. T</span></span></span></span></span></span></span></span><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="short_text" lang="en"><span
class=""><span id="result_box" class="" lang="en"><span
class=""><span id="result_box" class="" lang="en"><span
class="">hese two components are what made me
see different data between those calculated by
Therion and those calculated manually.<br>
</span></span></span></span></span></span></span></span></span></span><br>
<span id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="short_text" lang="en"><span
class=""><span id="result_box" class="" lang="en"><span
class=""><span id="result_box" class="" lang="en"><span
class=""><span id="result_box" class=""
lang="en"><span class="">After some more
checks, I have verified that Therion is
correctly calculating the average between</span></span></span></span>
fore/back bearings. MY MISTAKE. The issue is
closed. <br>
<br>
Best regards and thanks</span></span></span></span></span></span></span></span><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="short_text" lang="en"><span
class=""><span id="result_box" class="" lang="en"><span
class=""><span id="result_box" class="short_text"
lang="en"><span class=""> for the patience.</span></span><br>
<br>
Evaristo. <br>
<br>
</span></span></span></span></span></span></span></span><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="" lang="en"><span class=""><span
id="result_box" class="short_text" lang="en"><span
class=""><span id="result_box" class="" lang="en"><span
class=""><br>
</span></span></span></span></span></span></span></span>El
17/05/2018 a las 15:02, Wookey via Therion escribió:<br>
</div>
<blockquote type="cite"
cite="mid:20180517130233.mnrwkophloyut75t@mail.wookware.org">
<pre wrap="">On 2018-05-17 09:25 +0200, Evaristo Quiroga via Therion wrote:
</pre>
<blockquote type="cite">
<pre wrap="">El 17/05/2018 a las 0:36, Olly Betts escribió:
</pre>
</blockquote>
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap=""> I think the formula is too complicated. I purpose a simpler formula, like:
If bearing <=180
AverageBearing = (bearing + (backbearing -180))/2
else
AverageBearing = (bearing + (backbearing +180))/2
Your proposed formula gives wrong answers in some cases - consider:
bearing = 80, backbearing = 0
These give AverageBearing = (80 + 0 - 180) / 2 = -50 (equivalent to
310), but this should be 130 (average of 80 and 180).
In this case is not a problem with my formula, is a serious magnetic anomaly
(100 degrees difference) and the program should to stop and to send a warning.
</pre>
</blockquote>
<pre wrap="">
Yes a warning should probably be issued about poor data, but it _is_ a
problem with your formula. It's just an example showing that all cases
have to be dealt with correctly, including the wrap-around at 0/360
(or 0/400 for grads) and your simplified formula doesn't.
An example with a much smaller difference between back and foresight
could still be constructed to show the issue:
Fore: 175, Back: 0 AverageBearing= (175+0-180)/2 = -2.5. That's
wrong. It should be 177.5 in this case.
Wookey
</pre>
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</pre>
</blockquote>
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