Redundancy of elements

[PetrColinSky]

This issue is filed to keep the discussion we started during reviewing the schema in January 2022. It partly follows the issue #101 and also slightly issue #20 and others. There are some redundant elements in the schema. For example, <Latitude> and <Longitude> is within <Station> as well as under <Channel>. As <Channel> is inside <Station>, the <Latitude> and <Longitude> of the <Channel> could be inherited from <Station>, as it cannot be different (the same of <Elevation>).

Then, there are elements of <Channel>, which are often repeated for more channels of a seismic stations. These are:
<Latitude>,
<Longitude>,
<Elevation>,
<Depth>,
<SampleRate>,
<SampleRateRatio>,
<ClockDrift>,
<Sensor>,
<DataLogger> and
<Response>.
Generally, each component of a seismic sensor could have different transfer function, sure. Hence these elements need to be allowed inside each <Channel>. However, In practice, the <Response> is copied-pasted 3 times for all 3 channels. Repeating all PaZ and FIR filter coefficients 3 times for a classical seismic sensors seems impractical to me. Obviously, one cannot set it at the <Station> level, as station can have more instruments. To me, the nicest solution would be to have one more level between <Station> and <Channel>, something like <Instrument>, so that station can have 2 instruments, each having 3 channels. One instrument is very specific BB thing with individual <Response> for each channel, and hence the <Response> needs to be given separately for each <Channel>. The second instrument is only cheap thing with all properties defined just once for all 3 channels and hence the <Response> could be inherited from <Instrument>. This would not only save the space from repeating everything 3 times, but would also allow to clearly see, if the properties are the same or different channel to channel.

I also see some inconsistency of the elements listed at the same level: While <Latitude>, <Longitude>, <Elevation>, <Depth> and <Sensor> must be the same for all channels of the same instrument, and while <SampleRate>, <SampleRateRatio>, <ClockDrift>, <DataLogger> and <Response> can be either the same or different, there are two elements (<Azimuth> and <Dip>), which are in principle different for each component of a sensor. As they are at the same level as those which are in practice always the same, their more important presence here is bit hidden. To solve this would require a schema change.

[chad-earthscope]

There are some redundant elements in the schema. For example, <Latitude> and <Longitude> is within <Station> as well as under <Channel>. As <Channel> is inside <Station>, the <Latitude> and <Longitude> of the <Channel> could be inherited from <Station>, as it cannot be different (the same of <Elevation>).

Note that those are not redundant, while it is not as common, the station and the channel can have different coordinates for appropriate reasons. Example, a station that has multiple sensors (and then channels) that are physically spread out like a small array or sub-array element. If anything these scenarios will probably becomes more common in the future.

[crotwell]

See PR #6 for some old, but similar thoughts.