Re: [cf-pointobsconvention] Draft 2

Hi Keiran:

Keiran Millard wrote:
Catching up on the discussions after a week's holiday so I may be going
over old ground

In my opinion there seems to be a merging of issues that would benefit
from a bit of separation.

Firstly is the separation between the spatial position of the
instrument/ship and the spatial position of the phenomena being
measured, particularly wrt the Z coordinate.  In some cases they may be
the same but, not all.

I think I was trying to cover the case where you want to factor out the ship position, and have the sounding be reletive to it. If you dont care about that (or it differs at each point), you could store the ship position with each sounding observation.


The other separation is to treat Point, Profile, Section and
Trajectories as distinct feature types and not to collapse them.  I'm
taking definitions here from work of CSML (see
http://ndg.nerc.ac.uk/csml/ - particularly the user manual and
summarised below).  In this was you can be more specialised about a
given 'thing', e.g. a PointFeature doesn't require a Z attribute for
measurements, whereas a ProfileFeature, by its definition does.

PointFeature                    Single point measurement.       
PointSeriesFeature              Time-series of single datum measurements at a 
fixed location in space.
TrajectoryFeature               Measurement along a discrete path in time and 
space.    
PointCollectionFeature  Collection of distributed single datum measurements at 
a particular time
ProfileFeature          Single 'profile' of some parameter along a vertical 
line in space.
ProfileSeriesFeature            Time-series of profiles on fixed vertical 
levels at a fixed location
RaggedProfileSeriesFeature      Time-series of unequal-length profiles, but on 
fixed vertical levels, at a fixed location
SectionFeature          Series of profiles from positions along a trajectory in 
time and space.
RaggedSectionFeature            Series of profiles of unequal length along a 
trajectory in time and space       

We've been talking about comparing with CSML, perhaps we should go through that exercise now?


Incidentally I should add that I've been using the current ObsConvention
for storing fluvial data.  There are lots of similarities with marine
data, but the distribution of gauging stations are a bit like having a
collection met stations.  In my use case I have 'n' gauging stations
along a river network (=> different heights) measuring river flow (at
different depths), river depth, river temperature and various chemical
measurements.

Interesting. This does sound like a station collection. is there a z dimension to the sampling, or just a z coordinate at each guage station?


Best regards

Keiran