pvb
Well-Known Member
Wasn't DGPS largely superceded by the WAAS/EGNOS system, which all recent GPS receivers use?
Use of AIS in navigation
- Thread starter Dictys
- Start date
Wasn't DGPS largely superceded by the WAAS/EGNOS system, which all recent GPS receivers use?
JumbleDuck
Well-Known Member
I have never read a single post from any person who believes that AIS can replace the eyeball.
I have read several posts from people saying that with AIS and/or radar they feel safe to proceed at full speed in thick fog, which is much the same thing.
doug748
Well-Known Member
Interesting commercial development here:
lpdsn
Well-Known Member
In reality, doesn't it really depend upon what full speed is? Slowing down from a top speed of 5 Knots is unlikely to make much difference.
RichardS
N/A
In thick fog the eyeball is virtually useless .... so AIS probably has the edge in that very specific circumstance.
Richard
Uricanejack
Well-Known Member
I don't know, standard GPS may now be just as good. I suspect it is in some places but not in others. the Differential signal doesn't affect the GPS signals accuracy. It compares the GPS signal to the Charted position and provides a "correction" from the GPS to Chart. As far as I know some lighthouses are still equipped to do this.
Just pointing out some lighthouses do transmit GPS signals giving there position very accurately.
JumbleDuck
Well-Known Member
Differential GPS (DGPS) and the Wide Area Augmentation System (WAAS) do essentially the same thing, but in different ways. DGPS was a way of dealing with the large position errors in the civilian GPS signal which were caused by the Selective Availability (SA) system, under which large regions were given inaccurate GPS positions. DGPS stations knew where they were, and compared that with the position they got from GPS and broadcast the difference. Receovinging these signals, either with an enhanced GPS set or with a separate receiver, allowed the false position to be corrected.
WAAS does the same thing, but looks for much smaller errors in the ranges received from each satellite. These range errors arise from atmospheric conditions and (I think) fluctuations in the earth's magnetic field. WAAS was originally introduced by the FAA to give the added accuracy GPS needed for aviation use, and covers North America. The European Space Agency runs an equivalent, EGNOS (European Geostationary Navigation Overlay System).
Unlike DGPS, WAAS/EGNOS corrections are broadcast by satellite, and most GPS receivers use them as a matter of course. My old GPS72 is enabled for both WAAS and EGNOS.
I think that DGPS is still used in specialist applications where extremely high accuracy (millimetric or less) is needed, like archaeological surveying, but WAAS/EGNOS is good enough for the rest of us, and even that is probably overkill for most marine use now that SA is a distant memory.
prv
Well-Known Member
Nope, we've already established above that fixed AtoNs broadcast their official surveyed position, no GPS involved. What they send out will be exactly as accurate as the largest-scale chart.
Pete
JumbleDuck
Well-Known Member
I think we've established that that is what they should do, which may not necessarily be what they actually do ...
Things I Do Not Know But It's Late So Can't Be Bothered Looking Up #547: Do lighthouses and other aids to navigation transmit on the Class A scheme, the Class B scheme or a scheme of their own?
Lon nan Gruagach
Well-Known Member
simples: watch calculated (change in position, not transmitted) CoG. If a lighthouse moves its using GPS, if it dosent move it isnt using GPS.
lpdsn
Well-Known Member
Schemes of their own. Type 4 messages are used for base stations and type 21 for AtoNs. I think a lighthouse is a base station, but if I get a chance and I remember I'll check when next on the boat.