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

[Gary Pavlis]

vang and hang are defined in the CSS3.0 schema.  You have hang 
absolutely right. 
Here is the description of vang in dbhelp that is the detailed 
description of this attribute:

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.  See hang


An easier way for most people to think about it is that vang is the 
angle theta used in standard spherical
coordinates with z pointing up.

Gary Pavlis
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
>
>
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