Declination and the cs command
It seems the cs command over writes any declination that has been set, using the date provided with the survey data. I have a large batch of old data with some accurate local declinations given. Unfortunately these are overridden so I can’t compare my results with the original results. How can I make sure my local declinations are used rather than the cs global declination. Another problem on the same line. I have a set of data where the declination has been taken off the bearings, so the local declination is now 0 degrees but the cs command still adds a declination, moving it way out from its expected line. Can we have therion having a priority for local declinations rather than the gobal cs delinations ? John
If declination is explicitly specified for centerline, automatic declination is turned off. The reason, why you have a rotated map is probably "meridian convergence". I am not an expert in this topic, but coordinate system north is usually also rotated against true astronomical north. Have you played with layout north settings? E.g. include: north grid in the layout? Are you able to measure somehow this artificial rotation? Therion in its output reports both - calculated magnetic declination and meridian convergence for cave area. Another question? Do you measure declination against true (astronomical) or grid north? S. On 3 October 2012 13:54, John Stevens <john@k-stevens.co.uk> wrote:
It seems the cs command over writes any declination that has been set, using the date provided with the survey data.
I have a large batch of old data with some accurate local declinations given. Unfortunately these are overridden so I can’t compare my results with the original results. How can I make sure my local declinations are used rather than the cs global declination.
Another problem on the same line. I have a set of data where the declination has been taken off the bearings, so the local declination is now 0 degrees but the cs command still adds a declination, moving it way out from its expected line.
Can we have therion having a priority for local declinations rather than the gobal cs delinations ?
John
_______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion
The calibrations were to grid north not true north The little file help illustrate the problem. Either declination statement can be used (or both, as they don’t stack). If the cs command is commented out, we get a level square, but a rotated square if the cs command is used. So that was the solution, the difference between grid and true north. I then used the north true command and this rotated it to be level, north grid then moved it back. So back to north true. I am now unable to reproduce the the twisted again. I seem to be locked into this north command. Even when the declinations are commented out, I cant get it to use the cs declinations. Whoops! (yep I did restart the computer with no joy) John From: Stacho Mudrak Sent: Wednesday, October 03, 2012 2:04 PM To: List for Therion users Subject: Re: [Therion] Declination and the cs command If declination is explicitly specified for centerline, automatic declination is turned off. The reason, why you have a rotated map is probably "meridian convergence". I am not an expert in this topic, but coordinate system north is usually also rotated against true astronomical north. Have you played with layout north settings? E.g. include: north grid in the layout? Are you able to measure somehow this artificial rotation? Therion in its output reports both - calculated magnetic declination and meridian convergence for cave area. Another question? Do you measure declination against true (astronomical) or grid north? S. On 3 October 2012 13:54, John Stevens <john@k-stevens.co.uk> wrote: It seems the cs command over writes any declination that has been set, using the date provided with the survey data. I have a large batch of old data with some accurate local declinations given. Unfortunately these are overridden so I can’t compare my results with the original results. How can I make sure my local declinations are used rather than the cs global declination. Another problem on the same line. I have a set of data where the declination has been taken off the bearings, so the local declination is now 0 degrees but the cs command still adds a declination, moving it way out from its expected line. Can we have therion having a priority for local declinations rather than the gobal cs delinations ? John _______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion -------------------------------------------------------------------------------- _______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion -------------------------------------------------------------------------------- No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2221 / Virus Database: 2441/5306 - Release Date: 10/02/12
The problem of your sample data is, that you have cs specification after fix command in centerline. If you put cs OSGB:SO before "fix 1 10000 10000 0", then it starts to behave as it should. Otherwise this fix is in local coordinate system. Declination in therion is allways agains true north. So just substracting "meridian convergence" from declination specification should solve your problem. S. On 3 October 2012 16:41, John Stevens <john@k-stevens.co.uk> wrote:
The calibrations were to grid north not true north The little file help illustrate the problem. Either declination statement can be used (or both, as they don’t stack). If the cs command is commented out, we get a level square, but a rotated square if the cs command is used. So that was the solution, the difference between grid and true north.
I then used the north true command and this rotated it to be level, north grid then moved it back. So back to north true. I am now unable to reproduce the the twisted again. I seem to be locked into this north command. Even when the declinations are commented out, I cant get it to use the cs declinations. Whoops! (yep I did restart the computer with no joy)
John
From: Stacho Mudrak Sent: Wednesday, October 03, 2012 2:04 PM To: List for Therion users Subject: Re: [Therion] Declination and the cs command
If declination is explicitly specified for centerline, automatic declination is turned off.
The reason, why you have a rotated map is probably "meridian convergence". I am not an expert in this topic, but coordinate system north is usually also rotated against true astronomical north.
Have you played with layout north settings? E.g. include:
north grid
in the layout? Are you able to measure somehow this artificial rotation? Therion in its output reports both - calculated magnetic declination and meridian convergence for cave area.
Another question? Do you measure declination against true (astronomical) or grid north?
S.
On 3 October 2012 13:54, John Stevens <john@k-stevens.co.uk> wrote:
It seems the cs command over writes any declination that has been set, using the date provided with the survey data.
I have a large batch of old data with some accurate local declinations given. Unfortunately these are overridden so I can’t compare my results with the original results. How can I make sure my local declinations are used rather than the cs global declination.
Another problem on the same line. I have a set of data where the declination has been taken off the bearings, so the local declination is now 0 degrees but the cs command still adds a declination, moving it way out from its expected line.
Can we have therion having a priority for local declinations rather than the gobal cs delinations ?
John
_______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion
________________________________ _______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion
________________________________
No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2221 / Virus Database: 2441/5306 - Release Date: 10/02/12
_______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion
Thank you for the answer, I now see that Therion deals with declination in a slightly different way to Survex. So i will need to adjust all the calibrated data I have converted from Survex. It also explains why the gaps (closures) between caves has changed when some data was imported using a .3d file from Survex and others with the data converted into Therion. Rather than going through all my files and finding out the differing meridian convergence for each file and changing the declination figures. (this would make it hard to see where these figures have come from). Is there any problem with setting a compass calibration to take care of the meridian convergence and use my old declination readings? As in the attached file. John -----Original Message----- From: Stacho Mudrak Sent: Friday, October 05, 2012 1:22 PM To: List for Therion users Subject: Re: [Therion] Declination and the cs command The problem of your sample data is, that you have cs specification after fix command in centerline. If you put cs OSGB:SO before "fix 1 10000 10000 0", then it starts to behave as it should. Otherwise this fix is in local coordinate system. Declination in therion is allways agains true north. So just substracting "meridian convergence" from declination specification should solve your problem. S. On 3 October 2012 16:41, John Stevens <john@k-stevens.co.uk> wrote:
The calibrations were to grid north not true north The little file help illustrate the problem. Either declination statement can be used (or both, as they don’t stack). If the cs command is commented out, we get a level square, but a rotated square if the cs command is used. So that was the solution, the difference between grid and true north.
I then used the north true command and this rotated it to be level, north grid then moved it back. So back to north true. I am now unable to reproduce the the twisted again. I seem to be locked into this north command. Even when the declinations are commented out, I cant get it to use the cs declinations. Whoops! (yep I did restart the computer with no joy)
John
From: Stacho Mudrak Sent: Wednesday, October 03, 2012 2:04 PM To: List for Therion users Subject: Re: [Therion] Declination and the cs command
If declination is explicitly specified for centerline, automatic declination is turned off.
The reason, why you have a rotated map is probably "meridian convergence". I am not an expert in this topic, but coordinate system north is usually also rotated against true astronomical north.
Have you played with layout north settings? E.g. include:
north grid
in the layout? Are you able to measure somehow this artificial rotation? Therion in its output reports both - calculated magnetic declination and meridian convergence for cave area.
Another question? Do you measure declination against true (astronomical) or grid north?
S.
On 3 October 2012 13:54, John Stevens <john@k-stevens.co.uk> wrote:
It seems the cs command over writes any declination that has been set, using the date provided with the survey data.
I have a large batch of old data with some accurate local declinations given. Unfortunately these are overridden so I can’t compare my results with the original results. How can I make sure my local declinations are used rather than the cs global declination.
Another problem on the same line. I have a set of data where the declination has been taken off the bearings, so the local declination is now 0 degrees but the cs command still adds a declination, moving it way out from its expected line.
Can we have therion having a priority for local declinations rather than the gobal cs delinations ?
John
_______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion
________________________________ _______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion
________________________________
No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2221 / Virus Database: 2441/5306 - Release Date: 10/02/12
_______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion
_______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2221 / Virus Database: 2441/5310 - Release Date: 10/04/12
Do you mean adding some option, that would specify, that given declination is not against true but grid north? S.
As it was a test file I forgot to copy my normal statements across. I tend to use a line like declination xx degrees # xx.x degrees (based on Grid Bearing of 18.5 deg to Llangattock Church) to show the location of the calibrated bearing we have used. This line was set out over 40 years ago and most of the calibrations have been an average of 6 or so readings taken. I have now adapted a tripod so I can calibrate the distox on the same line. (most tripods have quite a bit of iron in them, so replace all with suitable non magnetic nuts and bolts, discarding any springs etc.) I have been taking calibration in each orientation of the distox, rotating one way then the other to get 8 hopefully similar readings. Then average to produce declination -1.8 degrees # 20.31 degrees (based on Grid Bearing of 18.5 deg to Llangattock Church) calibrate compass 0.9280 # meridian convergence for OSGB:SO location with the actual calibration readings in with the cave survey data but commented out. Maybe this is more how to use the distox and pda than Therion John From: Stacho Mudrak Sent: Thursday, October 11, 2012 4:48 PM To: List for Therion users Subject: Re: [Therion] Declination and the cs command Do you mean adding some option, that would specify, that given declination is not against true but grid north? S. -------------------------------------------------------------------------------- _______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion -------------------------------------------------------------------------------- No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2221 / Virus Database: 2441/5325 - Release Date: 10/11/12
Yes please - that would help a problem I have with the Upper Flood data where much of the "old" data is declined against Grid North, and hence all my "new" data has also been delcined to Grid North too. When I add the CS option, the data is rotated by 0.55 degrees (the Grid to True difference in UK). (First posted Feb 2011 under subjects "CS and grid alignmenrt" and "grid alignment rotation") Ben _____ From: therion-bounces@speleo.sk [mailto:therion-bounces@speleo.sk] On Behalf Of Stacho Mudrak Sent: 11 October 2012 16:49 To: List for Therion users Subject: Re: [Therion] Declination and the cs command Do you mean adding some option, that would specify, that given declination is not against true but grid north? S.
When trying to implement new feature we have figured out in literature, that declination against grid north is called "needle deflection". Is this english term, OK? It means, instead of declination, you would specify needle-deflection 10 deg In Slovakia, we call it "magnetic deflection". Or may be just declination-north grid would be sufficient. Any comments? S. On 14 October 2012 15:01, Ben Cooper <ben@caver.plus.com> wrote:
** Yes please - that would help a problem I have with the Upper Flood data where much of the "old" data is declined against Grid North, and hence all my "new" data has also been delcined to Grid North too. When I add the CS option, the data is rotated by 0.55 degrees (the Grid to True difference in UK).
(First posted Feb 2011 under subjects "CS and grid alignmenrt" and "grid alignment rotation") Ben
------------------------------ *From:* therion-bounces@speleo.sk [mailto:therion-bounces@speleo.sk] *On Behalf Of *Stacho Mudrak *Sent:* 11 October 2012 16:49
*To:* List for Therion users *Subject:* Re: [Therion] Declination and the cs command
Do you mean adding some option, that would specify, that given declination is not against true but grid north?
S.
_______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion
I wasn't certain of the correct terms to use either, but I found this on the British Ordnance Survey website: http://www.ordnancesurvey.co.uk/oswebsite/support/knowledgebase/grid-north-m... "The horizontal angular difference between True North and Magnetic North is called MAGNETIC VARIATION or DECLINATION. The horizontal angular difference between Grid North and Magnetic North is called GRID MAGNETIC ANGLE." Footleg On 25 October 2012 15:51, Stacho Mudrak <lists@group-s.sk> wrote:
When trying to implement new feature we have figured out in literature, that declination against grid north is called "needle deflection". Is this english term, OK? It means, instead of declination, you would specify
needle-deflection 10 deg
In Slovakia, we call it "magnetic deflection". Or may be just
declination-north grid
would be sufficient. Any comments?
S.
On 14 October 2012 15:01, Ben Cooper <ben@caver.plus.com> wrote:
Yes please - that would help a problem I have with the Upper Flood data where much of the "old" data is declined against Grid North, and hence all my "new" data has also been delcined to Grid North too. When I add the CS option, the data is rotated by 0.55 degrees (the Grid to True difference in UK).
(First posted Feb 2011 under subjects "CS and grid alignmenrt" and "grid alignment rotation") Ben
________________________________ From: therion-bounces@speleo.sk [mailto:therion-bounces@speleo.sk] On Behalf Of Stacho Mudrak Sent: 11 October 2012 16:49
To: List for Therion users Subject: Re: [Therion] Declination and the cs command
Do you mean adding some option, that would specify, that given declination is not against true but grid north?
S.
_______________________________________________ Therion mailing list Therion@speleo.sk http://mailman.speleo.sk/mailman/listinfo/therion
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participants (4)
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Ben Cooper -
Footleg -
John Stevens -
Stacho Mudrak