Grid convergence

[Mateusz Golicz]

Dears,

Now that we have all that great work on coordinate systems and automatic 
declination done (thanks!!!) ... I am a bit uneasy on grid convergence.

Let us consider this test. Suppose an unsuspecting user surveyed a very 
straight Chinese borehole in Austria. It starts with a huge entrance at 
station "0" and ends in a choke at station "1". Suppose they typed in 
something like this:

*begin test
*date 2015.08.01
*cs UTM33N
*cs out UTM33N
*fix 0 328000 5260000 2500
*declination auto 328000 5260000 2500
*entrance 0

*data normal from to tape compass clino
0	1	1000	-3.04	0
*end test

Let's say they can smell earth at station 1. They resolve to go out, 
take their GPS and dig for the entrance!

The IGRF declination for this area is 3.04, which is why Survex computes 
its position at 328000.57 52610000 2500.

The poor user has told Survex to do its computations in UTM33N, so why 
should they suspect it is wrong?

But it is. The way UTM works is that if you go 1000 m towards the north 
pole from 328000 5260000, you in fact are roughly at 328029 5260999, you 
like it or not. This is some 29 m away from what Survex indicates.

Of course this "entrance hunting" example is a bit strange, but I guess 
we all realize this has big consequences in closing loops in 
multiple-entrance, multiple-fix situations. How do "we" deal with this? 
Any plans to fix that? If not, shouldn't we at least warn the 
unsuspecting user in our manual?

Cheers!
Mateusz

PS. In case we are already well past this discussion - sorry for 
bothering you and please point me to the relevant thread!