GPS phones, etc.

[Julian Humphries]

>        Rechecking some notes I found with our catalogs, Dan Cassidy at
>Magellan told me that multichannel receivers do better at dealing with the
>selective availability problem than single-channel, but "differential" fixes
>with 2 receivers are the only way to get *much* better fixes.  Chances are
>that's not really necessary for most users on this list.
>

Thanks for the info.  Although for some general surveying, 100 m accuracy
may be enough, there are many biological surveys where individual habitats
or organisms (e.g. a tree or pool) need to replicably located.  I think the
open sky problem may be our biggest obstacle.  As people find solutions
please post here.

In my Forestry Supply catalog, I found a description of a product by
Magellan, that allows differential processing by a single receiver.
Evidently you take multiple readings from several locations (or times?) and
this add-on then resolves the readings into a more precise location (1
meter accuracy).   If this is not enough, evidently the only solution is a
base station receiver.

Isn't it ridiculous that all of this is necessary because of intentional
degradation of the signal?  Clearly any foreign governments that wanted to
used the current signals can design (or simply buy!) hardware and software
that gets around the degradation.

Finally, an amusing pricing story.  The Foresty Supply catalog has a
Magellan "Nav 5000 Pro" for $3750 (US).  Cabella's (fishing supplies) has
a Magellan "Nav 5000D" for $995.  The specs and pictures look identical,
although I suppose there could be some difference.

Julian Humphries
The Vertebrate Collections and The MUSE Project, Cornell University
Building 3, Research Park
83 Brown Road
Ithaca, NY  14850

Voice: 607-257-8143
Fax:   607-257-8109
Email: jmh3 at cornell.edu