[Antelope] Fwd: how does antelope define the axis vang in the ddbatch file?

[Jennifer Eakins]

Second attempt to get this sent out to the Antelope mail list using  
alternate email account.  If needed, please reply to eakins at brtt.com.

--Jennifer

Begin forwarded message:

From: Jennifer Eakins <eakins at brtt.com>
Date: October 7, 2008 5:46:10 PM MDT
To: Val Zimmer <valzimmer at berkeley.edu>
Cc: Antelope at brtt.net
Subject: Re: [Antelope] how does antelope define the axis vang in the  
ddbatch file?

Hi Valerie,

The hang/vang definitions are from the CSS3.0 schema and can be found  
by using the command:

	% dbhelp css3.0

Choose "Search for...".  Type vang.  You will see the description:

This attribute measures the angle between the sensitive
axis of a seismometer and the outward-pointing vertical
direction.  For a vertically oriented seismometer, vang =
0, or 180 (to reverse the sense of the instrument).  For a
horizontally oriented seismometer, vang = 90.

You can get full documentation in pdf format for all of the  
attributes in the css3.0 schema with the following set of commands:

     %   dbdoc css30 > dbdoc.out
     %   tbl dbdoc.out | troff -ms | /usr/lib/lp/postscript/dpost >  
dbdoc.ps
     %   ps2pdf dbdoc.ps

You also may have had questions regarding some other fields in the  
dbbuild batch file:

> axis <name> <hang> <vang>       ?     ?

 From the dbbuild_batch man page:

        axis label hang vang [sens [lead [pgain [pstage]]]]
        axis2 label hang vang [sens [dlgain [pgain [pstage [lead]]]]

An example from the dbbuild_examples man page for a sensor that was  
installed with the north arrow pointing south.  The modification of  
the hang value for the Z component is unnecessary.  There is no  
change to the vertical orientation shown in the example below.

    Swap sensor serial number and orientation
         # replace sensor, modify orientation

         time    4/27/2006       16:24:00
         net XX Some temporary deployment
         sta     EX03    33.4312 -116.4275 0.756  EX03
         datalogger Passcal_q330_linear  7753 XX_EX03
         sensor cmg3t    0       T3K33
         samplerate 40sps
         samplerate 1sps
         add

         time    08/02/2006      19:37:00
         cmg3t   0       T3K45
         axis Z 180 0
         axis N 180 90
         axis E 270 90
         add

         close EX03 1/1/2007   00:00:00

If you have an additional example that you wish to see included in  
the dbbuild_examples man page for the "tilted" setup, please forward  
the successfully tested batch file to me (via support at brtt.com) and I  
will update it.  I suspect that you need to put something like:

         axis Z 0 12
         axis N 0 102
         axis E 90 102		# 90 for horizontal(hang) + 12 degrees  
downward tilt.

if you have a vault floor tilted 12° down (below horizontal).

To add to the confusion, a dataless SEED volume uses azimuth and dip,  
not hang and vang.  For a "standard" setup, I believe the following  
is the correct mapping:

chan	az	dip		hang	vang
BHZ	0	-90		0	0
BHN	0	0		0	90
BHE	90	0		90	90


--Jennifer Eakins


On Oct 07, 2008, at 1:56 PM, Val Zimmer wrote:

> Hello Antelope users -
>
> I have a dataset from a station that was NOT placed perfectly level  
> - e.g. the sensor was placed on a ledge that had a little bit of  
> tilt, such that Z is not perfectly up/down, and N + E have some  
> down or upward component in the data.  I'm now trying to build a  
> database from that data, but have yet to find a good definition of  
> vang in the dbbatch file (for axis).   This is, of course,  
> something that the original programmers would have defined in the  
> source code, assuming antelope does something with that "axis"  
> component (as opposed to it being merely a comment).
>
> Having thought about this a while, I can think of only one good,  
> logical way to define vang, although, I'm probably missing  
> something, and would like to verify that this is correct.
> Here's an example from some documentation:
> axis <name> <hang> <vang>       ?     ?
> axis    Z            0         180         - 1     1
> axis    N            0         90          - 2     1
> axis    E            90         90         - 3     1
>
> hang (horizontal angle) has a well-defined, inherent, orientation  
> (N = 0, E = 90, S = 180, W = 270) and an normal viewpoint (map/ 
> above view, with N up, E right, etc).  Ok, easy, no problem.
>
> vang (vertical angle), however, has no inherent orientation,  
> although we can infer the following things from the above example,  
> assuming we are dealing with the earthquake seismology definition  
> (e.g. +Z is up, NOT down like in the oilfield):  Up = 180, Down =  
> 0.  Of course, there is no "normal" viewpoint when it comes to  
> cross-sectional views, and trying to define one is bound to confuse  
> and contradict, therefore, the direction of the vang vector *must*  
> be relative to the hang vector AND that <vang> vector corresponds  
> to apparent tilt along that vector (not absolute/maximum tilt for  
> the whole instrument in whatever direction that happens to be).
> Therefore, I *think* the only possible way to define it would be  
> that <vang> must be 0-> 180 and that the vector points in the same  
> direction of the <hang> vector, and it doesn't matter whether 90  
> degrees is to the "right" or to the "left" since that totally  
> depends on the perspective.  Hence, it follows that:
>
> axis  S        180    90 (not, and never 270)
> axis W       180     90
>
> axis N+ a little up          0       110
> axis E + a little down     90      75
>
> Can anyone tell me if this reasoning is correct, and if not, point  
> me to some documentation with a clear definition?
>
> Thanks for your time!
> Valerie Zimmer
>
>
> _______________________________________________
> Antelope mailing list
> Antelope at brtt.net
> http://brtt.net/mailman/listinfo/antelope_brtt.net



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