On Fri, 15 Jul 2005 11:39:51 -0400, Anchor
wrote:

In this case the idea that the Gatun Cut causes GPS satellite visibility
issues is nonsense and the idea must be rejected and deleted from your
knowledge base.

The cut is far from a canyon with steep walls. There is plenty of sky for
the GPS to see satellites.

WAAS has nothing to do with it.

Our primitive 1995 vintage Garmin 45 pseudo-tracker multiplexed GPS worked
just fine when we went through the Gatun Cut in January of 1998.


FWIW
The only place we have lost GPS reception was during transiting the Corinth
Canal in Greece.

Peter

On Fri, 15 Jul 2005 22:11:05 +0000, Gordon Wedman wrote:


"Anchor" wrote in message
.. .
On Wed, 13 Jul 2005 22:02:44 -0400, Larry wrote:

"FMac" wrote in
:


Have you gone through the Canal? If so, explain what mountains you
noticed. I didn't see any mountains, but I did see and experience a
"Cut". The cut was a bit narrow, but not for a medium sized
sailboat.
We spent an overnight in the big lake, caught a few fish, had a
great
dinner and pressed on the following morning. The canal is not a
navigational thing, it is nothing more than mere piloting. That
said, I'm aware the transit price has gone up considerably since my
transit in the mid "90's".




Never been through the canal. My post was from a news item I found on
a maritime website. The idea was the canyon it's in may cause poor
reception of WAAS satellite correction data.

Ideas are fine but modern science dictates one dismisses ideas and
rejects theories that do not apply.

In this case the idea that the Gatun Cut causes GPS satellite
visibility issues is nonsense and the idea must be rejected and deleted
from your knowledge base.

The cut is far from a canyon with steep walls. There is plenty of sky
for the GPS to see satellites.

WAAS has nothing to do with it.

Our primitive 1995 vintage Garmin 45 pseudo-tracker multiplexed GPS
worked just fine when we went through the Gatun Cut in January of 1998.

You don't have to be in a canyon to have WAAS problems. I live in
Nanaimo which is on the East side of Vancouver Island. We have high
land to the west and my Garmin GPSMap 182 cannot get a WAAS signal in my
marina. It receives GPS satellite signals without trouble but the WAAS
satellites are low in the south-west and apparently the hills shadow
this signal. Further away from shore I can pick up WAAS signals.

There seems to be some confusion between WAAS and DGPS.

WAAS is on on some GPS satellites, not all. If a GPS can see a WAAS
equipped satellite, it has WAAS information for that satellite. Clearly
if a satellite, WAAS or non WAAS, is in shadow the GPS cannot use that
satellite. A WAAS GPS will need 3 or more WAAS satellites to produce a
WAAS fix. Three or more satellites but less than 3 WAAS satellites in
view generates an ordinary fix. This has nothing to do with whether or
not you are in harbor.

Satellites are never in shadow in open water. Define open water for GPS
satellite viewing purposes to be "nothing on the horizon".

Parts of a vessel may shadow a GPS antenna if the antenna is mounted low
and below some large vessel component such as a smoke stack. It is clear
geometry. If an eye ball at the GPS antenna position can see the horizon,
so can the GPS antenna.

Some GPS manufactures refer to a WAAS fix as a differential fix. This is
a poor choice of nomenclature because a WAAS fix is a WAAS fix, not a
differential DGPS fix.

DGPS relies on land based LF transmitters to broadcast differential
corrections. Poor reception of these DGPS signals will result in loss of
DGPS capability. If your harbour is sheltered from DGPS reception, you
will not have DGPS capability in that harbor.

If the DGPS signal is receivable by AIS equipped vessel in the Gatun Cut,
all DGPS equipped vessel can receive it or there is something wrong with
the DGPS installation on board vessels that cannot receive it.

On Sat, 16 Jul 2005 08:43:33 -0400, Anchor
wrote:



There seems to be some confusion between WAAS and DGPS.

Yes, I can see that from your message...

WAAS is on on some GPS satellites, not all. If a GPS can see a WAAS
equipped satellite, it has WAAS information for that satellite. Clearly
if a satellite, WAAS or non WAAS, is in shadow the GPS cannot use that
satellite. A WAAS GPS will need 3 or more WAAS satellites to produce a
WAAS fix. Three or more satellites but less than 3 WAAS satellites in
view generates an ordinary fix. This has nothing to do with whether or
not you are in harbor.

WAAS correction data is transmitted by two (Inmarsat?) geosynchronous
satellites, not by any of the normal GPS satellites.

WAAS collects correction data from a network of reference stations in
the US, and uploads that data (after some processing) to the
satellites for rebroadcast. The correction data is only useful at
location inside, or near, the reference station network - if you
attempt to use the data in distant locations, you may increase
positioning errors, rather than reduce them.

Some GPS manufactures refer to a WAAS fix as a differential fix. This is
a poor choice of nomenclature because a WAAS fix is a WAAS fix, not a
differential DGPS fix.

WAAS is a form of differential correction, so I believe it is valid to
consider a WAAS-corrected fix a differential corrected fix.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

"Peter Bennett" wrote in message
news.com...
On Sat, 16 Jul 2005 08:43:33 -0400, Anchor
wrote:



There seems to be some confusion between WAAS and DGPS.

Yes, I can see that from your message...

WAAS is on on some GPS satellites, not all. If a GPS can see a WAAS
equipped satellite, it has WAAS information for that satellite. Clearly
if a satellite, WAAS or non WAAS, is in shadow the GPS cannot use that
satellite. A WAAS GPS will need 3 or more WAAS satellites to produce a
WAAS fix. Three or more satellites but less than 3 WAAS satellites in
view generates an ordinary fix. This has nothing to do with whether or
not you are in harbor.

WAAS correction data is transmitted by two (Inmarsat?) geosynchronous
satellites, not by any of the normal GPS satellites.

WAAS collects correction data from a network of reference stations in
the US, and uploads that data (after some processing) to the
satellites for rebroadcast. The correction data is only useful at
location inside, or near, the reference station network - if you
attempt to use the data in distant locations, you may increase
positioning errors, rather than reduce them.

Some GPS manufactures refer to a WAAS fix as a differential fix. This is
a poor choice of nomenclature because a WAAS fix is a WAAS fix, not a
differential DGPS fix.

WAAS is a form of differential correction, so I believe it is valid to
consider a WAAS-corrected fix a differential corrected fix.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

Getting down to the basic, WAAS is nothing more than an add-on to GPS by the
FAA. The basic function is to correct the GPS CEP from 100 meters to 3
meters and is only functional in some of the Americas.

Peter Bennett wrote in
news.com:

WAAS correction data is transmitted by two (Inmarsat?) geosynchronous
satellites, not by any of the normal GPS satellites.


I wonder if the reason the Canal is not using them is the canal is below
the footprint, probably pointed at the USA?? Geo-birds use very directive
antenna arrays to produce a useable signal from 40-50K miles away. They
usually have a fixed footprint that looks like an oval over the states with
these antennas. Maybe WAAS doesn't work in Panama so well because of
this??

--
Larry

On Sat, 16 Jul 2005 19:33:11 -0400, Larry wrote:

Peter Bennett wrote in
rnews.com:

WAAS correction data is transmitted by two (Inmarsat?) geosynchronous
satellites, not by any of the normal GPS satellites.


I wonder if the reason the Canal is not using them is the canal is below
the footprint, probably pointed at the USA?? Geo-birds use very directive
antenna arrays to produce a useable signal from 40-50K miles away. They
usually have a fixed footprint that looks like an oval over the states with
these antennas. Maybe WAAS doesn't work in Panama so well because of
this??

The Panama Canal is likely too far outside the network of reference
stations used for creating the WAAS correction data for the data to be
considered reliable.


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

On Sat, 16 Jul 2005 10:30:26 -0700, Peter Bennett wrote:

On Sat, 16 Jul 2005 08:43:33 -0400, Anchor
wrote:



There seems to be some confusion between WAAS and DGPS.

Yes, I can see that from your message...

WAAS is on on some GPS satellites, not all. If a GPS can see a WAAS
equipped satellite, it has WAAS information for that satellite. Clearly
if a satellite, WAAS or non WAAS, is in shadow the GPS cannot use that
satellite. A WAAS GPS will need 3 or more WAAS satellites to produce a
WAAS fix. Three or more satellites but less than 3 WAAS satellites in
view generates an ordinary fix. This has nothing to do with whether or
not you are in harbor.

WAAS correction data is transmitted by two (Inmarsat?) geosynchronous
satellites, not by any of the normal GPS satellites.

WAAS collects correction data from a network of reference stations in
the US, and uploads that data (after some processing) to the
satellites for rebroadcast. The correction data is only useful at
location inside, or near, the reference station network - if you
attempt to use the data in distant locations, you may increase
positioning errors, rather than reduce them.

Some GPS manufactures refer to a WAAS fix as a differential fix. This is
a poor choice of nomenclature because a WAAS fix is a WAAS fix, not a
differential DGPS fix.

WAAS is a form of differential correction, so I believe it is valid to
consider a WAAS-corrected fix a differential corrected fix.

Hello Peter,

Absolutely but here in is the cause of the confusion:
1. WAAS - satellite based differential
2. DGPS - terrestial based differential

WAAS is not DGS and DGPS is not WAAS, but they are both differential.

Surveyors survey sub divisions to to 2 cm accuracy by establishing a local
DGPS system which consists of
o ground station
* dual frequency L1/L2 GPS receiver
* RTCM differential correction calculating computer
* RTCM differential correction transmitter w/antenna
(400-500 MHz UHF)
o survey station (handheld)
* dual frequency L1/L2 DGPS receiver
* RTCM differential correction UHF receiver

The ground station is set up where the position is known with precision,
like right on top of a survey benchmark. Turn it on, enter the lat, lon,
elevation and the system is operational.

Options include the RF power and directional or uni-directional antennas.

My brother in law makes his living doing DGPS surveys.

Greg Blair

On Sat, 16 Jul 2005 10:30:26 -0700, Peter Bennett wrote:

On Sat, 16 Jul 2005 08:43:33 -0400, Anchor
wrote:



There seems to be some confusion between WAAS and DGPS.

Yes, I can see that from your message...

WAAS is on on some GPS satellites, not all. If a GPS can see a WAAS
equipped satellite, it has WAAS information for that satellite. Clearly
if a satellite, WAAS or non WAAS, is in shadow the GPS cannot use that
satellite. A WAAS GPS will need 3 or more WAAS satellites to produce a
WAAS fix. Three or more satellites but less than 3 WAAS satellites in
view generates an ordinary fix. This has nothing to do with whether or
not you are in harbor.

WAAS correction data is transmitted by two (Inmarsat?) geosynchronous
satellites, not by any of the normal GPS satellites.

WAAS collects correction data from a network of reference stations in
the US, and uploads that data (after some processing) to the
satellites for rebroadcast. The correction data is only useful at
location inside, or near, the reference station network - if you
attempt to use the data in distant locations, you may increase
positioning errors, rather than reduce them.

Some GPS manufactures refer to a WAAS fix as a differential fix. This is
a poor choice of nomenclature because a WAAS fix is a WAAS fix, not a
differential DGPS fix.

WAAS is a form of differential correction, so I believe it is valid to
consider a WAAS-corrected fix a differential corrected fix.

I was mistaken about the satellites.

WAAS does not use GPS satellites.

http://gpsinformation.net/exe/waas.html

Our Garmin 76 reported WAAS GPS fixes on the east coast of Australia and
New Zealand in late 2002.

AFAIK there is no absolute law requiring all passage of recreational
vessels to be granted, and we are lucky we may use it with the minor
inconvenience of a $150 navaid rental in certain cases.