Just want to point out that many of our older datasets, which are
still available - and actually still used - predate the routine use of
GPS on ships. These datasets are from buoys that were set using
dead reckoning.
And, although we now have pretty nearly exact anchor positions,
the buoys on our moorings deployed in about 5 km of water
typically have 5 km watch circle diameters.
So, although the datum specification should be encouraged, there's
a definite drawback to assuming a default. And, the position's accuracy
is probably more significant than the datum spec for a lot of in situ data-
so we should really encourage the use of QC terms for all coordinates.
Thanks - Nan
Mike Grant wrote:
> On 19/04/10 15:43, Jonathan Blower wrote:
>
>> specification, which datum should be assumed? Spherical Earth? WGS84?
>>
>
> If you're picking one at random, I'd go for WGS84 - that's a pretty safe
> bet for a lot of remote sensed and GPS related data.
>
> Cheers,
>
> Mike.
>
>
>
>> Hi all,
>>
>> The CF conventions define a means to specify the datum used in certain
>> map projections
>> (http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.4/cf-conventions.ht
>> ml#grid-mappings-and-projections). In the (common) case of a data file
>> containing latitude and longitude axes, but no explicit datum
>> specification, which datum should be assumed? Spherical Earth? WGS84?
>>
>> The horizontal error resulting from use of an incorrect datum can be
>> significant for high-resolution and/or local dataset (hundreds of
>> metres).
>>
>> Cheers, Jon
--
*******************************************************
* Nan Galbraith (508) 289-2444 *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 *
*******************************************************
Received on Mon Apr 19 2010 - 09:48:38 BST
