[Therion] Calibration of co-ordinate systems

[Andrew Atkinson]

I will try to explain a little more to help clarify. (we will ignore te 
uneven numbers for now to stick to one topic)

In the OSGB it is typical to quote 10 figure grid references to fix a 
location to 1m EG
47130 56380

Strictly this identifies a location within a 100km square the is 
referred to with a 2 letter code so the above should be

ST 47130 56380

However, it is common to miss out the ST if it is clear what area you 
are talking about, ie a Mendip cave.


Now these 10 figure grid references are fine for putting systems 
together, however to get a kml output, in the right place, I need to add 
300000 10000 which I can do, but makes the files a bit confusing to 
people that do not understand co-ordinate systems. (And I am trying to 
get lots of people to be able to contribute to the area map, so 
simplicity is important)

Now when importing a 3d file it is possible to use calibrate option to 
add the 300000 100000 but I cannot find a way to do this to all the th 
files I have, so I would have to go through all the fixed stations and 
do it manually.

It would seem sensible to be able to work in these local co-ordinates 
until the output of the kml and then do the a calibrate to add the 30000 
10000. (I am sure there must be similar situations in other countries.)
I am hoping there is a way to do this and I am just been incapable of 
finding it. From other function is Therion such as prefix etc, it would 
seem to fit the pattern of construction.

(It is simple to do it manually if it is 30000 10000 but if it is 299912 
99991 it will be far more tedious)

hope this is clearer and a solution that does not involve me manually 
editing tens of fixed locations is possible

thanks

Andrew

Wolfgang Zillig wrote:
> Hi Andrew,
> 
> I'm not sure if I understand your problem correctly. There is on issue 
> with the EPSG codes for OSGB36, see:
> http://osgeo-org.1803224.n2.nabble.com/EPSG-27700-td4469120.html
> and
> http://www.osgeo.org/pipermail/grass-user/2009-July/051494.html
> 
> But this could explain your uneven numbers in the calibrate command. Can 
> it be that the coordinate fix misses some leading numbers? The skipping 
> is sometimes common to avoid huge numbers. Can you check this by 
> converting some coordinates from WGS84 (for instance) to OSGB36?
> 
> Best regards
> Wolfgang
> 
> Am 17.05.2010 23:17, schrieb Andrew Atkinson:
>> Hi
>>
>> I am having a little bit of difficulty with the various different 
>> helps on co-ordinate systems. I am building an area survey map from 
>> data from various different sources, so having to 'adapt' it, but 
>> really do not want to have to convert it all. It would be nice to have 
>> one of the outputs as .kml for google earth and the like.
>>
>> Lots of the data is in Survex, with Local OSGB 6 figure grid 
>> references. These I have been importing eg
>>
>> import Great_Swallet.3d -surveys use -filter great_swallet -cs 
>> EPSG:27700 -calibrate [0 0 0 299912 99991 0]
>> #Should be -calibrate [0 0 0 300000 100000 0]
>>
>> (goodness knows why the calibrate is not right, the bodge is to align 
>> it on goodle earth, probably my ignorance)
>>
>>
>> As most of the new data is in Pockettopo imported, into therion, is 
>> attached to the survex data this has worked well.
>> One cave entrance has been done in therion direct but I just dealt 
>> with that by doing the calibrate manually
>>
>> I have now been sent lots of data with lots (60 fix #ed points or 
>> more) of cave entrances, all in therion with local 6 figure grid 
>> references.
>>
>> I can set the coordinate system to EPSG:27700 by adding it within the 
>> centreline/endcentre, but that puts the cave in the Atlantic 
>> somewhere. So using
>> centreline -cs EPSG:27700 -calibrate [0 0 0 299912 99991 0]
>> gives the error
>>
>> not enough option arguments -- -calibrate -- must be 2
>>
>> Which is fair enough as calibrate is already used in the centreline 
>> for correcting a zero error.
>>
>> Not to be easily put off I tried it the other way round, remove the 
>> calibrate from the centreline and use
>>
>> cs EPSG:27700 in the config files to get therion to output in these 
>> coordinates, however although I can get the caves relatively next to 
>> each other, the kml puts them in the Atlantic again and
>>
>> cs EPSG:27700 -calibrate [0 0 0 299912 99991 0]
>>
>> gives error
>>
>> output coordinate system specification requires single parameter
>>
>>
>> and
>>
>> cs EPSG:27700
>> calibrate [0 0 0 299912 99991 0]
>>
>> gives error
>>
>> unknown configuration command -- calibrate
>>
>> Have I missed something or do I need to go through and add 300000 and 
>> 100000 to all the fixed points. If this is so, could we have a 
>> calibratecs to use with the cs command to overcome localised 
>> coordinates on a national grid, the UK cannot be the only country with 
>> this problem, and it must be easier to work mainly in the more 
>> localised coordinates and calibrate it on output
>>
>> hope this all makes sense,
>>
>> Andrew
>>
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