Re: [cf-pointobsconvention] Draft 2

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Hi Keiran-

Thanks for the pointer to the CSML docs.  It seems like there is
some convergence of ideas. I have a couple of questions:

- how are multiple data at a point handled?  PointFeature seems to
imply only one measurement (datum) (as does PointCollectionFeature)
- how are time series of PointCollectionFeature handled.  I don't
see a PointCollectionSeriesFeature

My use case is to plot METAR observations in a standard station
model format (Temp, Dewpoint, Pressure, etc) over a region and animating
them through time.  This is probably the most common way of looking
at station observations in synoptic meteorology.


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.
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 - 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    

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
Best regards


Don Murray                               UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307

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