[Taxacom] Geodetic datums do matter

Frederick W Schueler bckcdb at istar.ca
Mon Mar 23 14:10:17 CDT 2009

Doug Yanega wrote:

>  I am conversely fond of telling him that when a team of 
> entomologists goes into the field to collect specimens, we take a GPS 
> reading where we park the car, and then each person is free to wander 
> - maybe a kilometer or more distant, collecting dozens of specimens 
> at random points anywhere within that radius. There is SO MUCH ERROR 
> associated with the specimens bearing that GPS reading on their 
> labels that it is no longer relevant what datum it was based on...

>  An error of 
> 200m may seem massive if you're trying to find a single, immobile 
> target, but a lot of what biologists deal with are not single 
> immobile targets! 
>  Accordingly, 
> it is genuinely pointless in such a context to *worry* about the 
> datum used.

* I don't know: certainly there are many situations where 200m doesn't 
matter, but there have been many times when a GPS has led me to the spot 
where a single specimen of a nearly-sessile snail was taken by a 
deceased colleague, or from which declining frogs had been heard 
calling, or where a particular rare plant had been discovered, or a 
colony of an invasive plant had been found. In these cases a 200m error 
or uncertainty would have ruined the replication I was trying to 
achieve. In the case of the GPS reading made at the roadside when 
collectors fan out to some distance, I use an ACCURACY field which 
starts as the usual uncertainty of the waypoint, but is enlarged to a 
description like "300m along road SW of site" or "250m around waypoint" 
to describe the uncertainty of the location.

For herpetology, malacology, and invasive plants, I'd say that 10m of 
error is acceptable, but not much more.

             Bishops Mills Natural History Centre
           Frederick W. Schueler & Aleta Karstad
        RR#2 Bishops Mills, Ontario, Canada K0G 1T0
     on the Smiths Falls Limestone Plain 44* 52'N 75* 42'W
       (613)258-3107 <bckcdb at istar.ca> http://pinicola.ca

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