[Auscope-geosciml] boo-boo in GeologicEvent [SEC=UNCLASSIFIED]
Oliver.Raymond at ga.gov.au
Oliver.Raymond at ga.gov.au
Fri Sep 25 14:41:50 EDT 2009
I agree. Time range for events is defined by 2 time positions, not a length of time. This extract from the Nth American Stratigrapic Code suggests that the units (Ma) for these time positions are positive numbers with units = Ma:
"The age of a stratigraphic unit or the time of a geologic event, as commonly determined by numerical dating or by reference to a calibrated time-scale, may be expressed in years before the present. The unit of time is the modern year as presently recognized worldwide. Recommended (but not mandatory) abbreviations for such ages are SI (International System of Units) multipliers coupled with "a" for annum: ka, Ma, and Ga for kilo-annum (103 years), Mega-annum (106 years), and Giga-annum (109 years), respectively. Use of these terms after the age value follows the convention established in the field of C-14 dating. The "present" refers to 1950 AD, and such qualifiers as "ago" or "before the present" are omitted after the value because measurement of the duration from the present to the past is implicit in the designation. In contrast, the duration of a remote interval of geologic time, as a number of years, should not be expressed by the same symbols. Abbreviations for numbers of years, without reference to the present, are informal (e.g., y or yr for years; my, m.y., or m.yr. for millions of years; and so forth, as preference dictates). For example, boundaries of the Late Cretaceous Epoch currently are calibrated at 63 Ma and 96 Ma, but the interval of time represented by this epoch is 33 m.y."
I had a play with making a CGI_NumericTimeRange element, defined by an upper and lower TM_Coordinate. BUT... there is a mandatory association with TM_CoordinateSystem which involves defining a timescale based on clock and calendar. (See attached picture to see the TM classes involved). Not very applicable to defining the geological time frame.
Another option was to utilise StratigraphicDateEstimate instead of TM_Coordinate, BUT... (i) the same problem with TM_CoordinateSystem arises and (ii) the StratigraphicDateEstimate inherits from TM_Position which allows more than just number age dates. (I think StratigraphicDateEstimate needs re-modelling.)
In summary, given the limitations of TM elements, Steve's proposal to use CGI_NumericRange to deliver numeric age values using the geologic timescale seems to be a good solution.
From: auscope-geosciml-bounces at lists.arcs.org.au [mailto:auscope-geosciml-bounces at lists.arcs.org.au <mailto:auscope-geosciml-bounces at lists.arcs.org.au> ] On Behalf Of stephen richard
Sent: Saturday, 26 September 2009 3:30 AM
To: Simon Cox
Cc: auscope-geosciml at lists.arcs.org.au
Subject: Re: [Auscope-geosciml] boo-boo in GeologicEvent
I think we're talking about position on a timeline, with a CRS set up such that origin is 1950, and positive is older steve
Simon Cox wrote:
> Yes - TM_Period is about a discrete interval, not uncertainty.
> There is also the matter of whether 'age' means
> - position on a timeline, a coordinate
> - the conventional origins make this a negative number for most
> geological events
> - amount of time embodied in (or 'since') the event, a quantity
> I.e. interval- vs. ratio-scale.
> Simon Cox
> European Commission, Joint Research Centre, Institute for Environment
> and Sustainability, Spatial Data Infrastructures Unit, TP 262 Via E.
> Fermi, 2749, I-21027 Ispra (VA), Italy
> Tel: +39 0332 78 3652
> Fax: +39 0332 78 6325
> mailto:simon.cox at jrc.ec.europa.eu <mailto:simon.cox at jrc.ec.europa.eu>
> http://ies.jrc.ec.europa.eu/simon-cox <http://ies.jrc.ec.europa.eu/simon-cox>
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> JRC: http://www.jrc.ec.europa.eu/ <http://www.jrc.ec.europa.eu/>
> -----Original Message-----
> From: auscope-geosciml-bounces at lists.arcs.org.au
> [mailto:auscope-geosciml-bounces at lists.arcs.org.au <mailto:auscope-geosciml-bounces at lists.arcs.org.au> ] On Behalf Of
> stephen richard
> Sent: Friday, 25 September 2009 14:00
> To: auscope-geosciml at lists.arcs.org.au
> Subject: [Auscope-geosciml] boo-boo in GeologicEvent
> There was some uncertainty on my part yesterday as to whether
> TM_Period is the correct type for numericAgeDate. After studying the
> ISO 19108 temporalSchema some more, I conclude its not; it only allows
> a time coordinate specified by a single number, no uncertainty. I
> recommend we change TM_Period to CGI_NumericRange; this is more
> consistent with the rest of the model, represents what we want better,
> and avoids another proxy for a
> GML3.2 element for v. 3 testing.
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