Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 26-08-2015, 21:14   #31
Registered User
 
markpierce's Avatar

Join Date: Aug 2010
Location: Central California
Boat: M/V Carquinez Coot
Posts: 3,413
Re: GPS accuracy

I'm more concerned with the accuracy of charts.
__________________

__________________
Kar-KEEN-ez Koot
markpierce is offline   Reply With Quote
Old 27-08-2015, 04:54   #32
Registered User
 
phiggins's Avatar

Join Date: Nov 2004
Location: Toronto, Canada
Posts: 1,288
Send a message via Skype™ to phiggins
Re: GPS accuracy

OK so we finally figured out the pattern is just the highlighting. If I turn off track highlighting and raise the Tracking Precision to high and run my GPS test for a few hours I get the attached results. It indicates the worse GPS reading was off by 9 meters for this GPS at this position at this time. Just nice to know.
Attached Thumbnails
Click image for larger version

Name:	GPS_Track.jpg
Views:	76
Size:	299.8 KB
ID:	108002  
__________________

__________________
Paul,
" One moment you are running along, the next you are no more." Dean Spanley
phiggins is offline   Reply With Quote
Old 27-08-2015, 05:58   #33
Registered User
 
transmitterdan's Avatar

Join Date: Oct 2011
Boat: Valiant 42
Posts: 4,019
Re: GPS accuracy

Not really that useful though. That particular "accuracy" is not going to be the same on the high seas. So depending on it is not a good idea.
__________________
transmitterdan is offline   Reply With Quote
Old 27-08-2015, 06:01   #34
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: GPS accuracy

Quote:
Originally Posted by phiggins View Post
It indicates the worse GPS reading was off by 9 meters for this GPS at this position at this time. Just nice to know.
Hopefully it didn't cause you to take a dump in the sink or anything too badů

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 27-08-2015, 06:15   #35
Registered User
 
phiggins's Avatar

Join Date: Nov 2004
Location: Toronto, Canada
Posts: 1,288
Send a message via Skype™ to phiggins
Re: GPS accuracy

Quote:
Not really that useful though. That particular "accuracy" is not going to be the same on the high seas. So depending on it is not a good idea.
Well I would think it would be a lot better where the GPS is open to the skies. Here the GPS is in the house, surrounded by trees and 100 meters from high voltage power lines.
__________________
Paul,
" One moment you are running along, the next you are no more." Dean Spanley
phiggins is offline   Reply With Quote
Old 27-08-2015, 06:19   #36
bcn
Registered User

Join Date: May 2011
Location: underway whenever possible
Boat: Rangeboat 39
Posts: 2,752
Re: GPS accuracy

Right, open sky (even with a GPS indoors but in cases of a steel/aluminium/carbon fibre house), no obstructions and no multi path.
Should do better.
__________________
bcn is offline   Reply With Quote
Old 27-08-2015, 06:28   #37
Registered User
 
transmitterdan's Avatar

Join Date: Oct 2011
Boat: Valiant 42
Posts: 4,019
Re: GPS accuracy

Maybe it will be better or maybe worse. You just can't be sure is all I'm saying. Therefore, there is no point in knowing the accuracy for it will surely change. There are no decisions that can be made on the basis of GPS accuracy in the range of meters. For close quarters work it's better to use other means such as depth and eyes.

I'm not saying GPS is useless. It is very good and more reliable than any other technique.
__________________
transmitterdan is offline   Reply With Quote
Old 27-08-2015, 06:31   #38
bcn
Registered User

Join Date: May 2011
Location: underway whenever possible
Boat: Rangeboat 39
Posts: 2,752
Re: GPS accuracy

Dan,

we agree: no automatic docking please

Hubert
__________________
bcn is offline   Reply With Quote
Old 27-08-2015, 08:47   #39
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
Re: GPS accuracy

Quote:
Originally Posted by transmitterdan View Post
What method of determining speed and position has greater accuracy than GPS?
Off the top of my head I could imagine at lest two:

- visual,

- mixed gnss.

Still, mixed gnss will likely incorporate gps as a component.

Possibly, maybe, an inertial system could be more accurate. But this one is only a guess.

b.
__________________
barnakiel is offline   Reply With Quote
Old 27-08-2015, 08:49   #40
Registered User
 
HappySeagull's Avatar

Join Date: Dec 2010
Location: B.C.,Canada
Boat: 29'
Posts: 2,395
Re: GPS accuracy

9 meters is pretty good, given where you are but If you are looking for trouble, consider the Vertical plane.. That'll get you trying to choose between geoid models. Most boats are airborne or submarines if you ask the gps on wgs84.

agree usually faster,better fix on water or prairie. I have drifted into dark coves at night with a pikepole feeling for steep shore and have found gps to be pretty darn good
__________________
HappySeagull is offline   Reply With Quote
Old 27-08-2015, 08:53   #41
bcn
Registered User

Join Date: May 2011
Location: underway whenever possible
Boat: Rangeboat 39
Posts: 2,752
Re: GPS accuracy

Yes, a combined Inertial/GNSS IMU will give a quite precise and high bandwidth solution.

Positioning will not be better than the specs of the GPS - so depending on the type of receiver and differential corrections but you can get rid of those spikes of the GPS shown on the screen shots = 3m bare/ 1.80m WAAS/ < 1m with differential corrections in real time.
And you will get a very good heading signal.
Not a inexpensive solution though...

Hubert
__________________
bcn is offline   Reply With Quote
Old 27-08-2015, 08:59   #42
bcn
Registered User

Join Date: May 2011
Location: underway whenever possible
Boat: Rangeboat 39
Posts: 2,752
Re: GPS accuracy

Quote:
Originally Posted by HappySeagull View Post
9 meters is pretty good, given where you are but If you are looking for trouble, consider the Vertical plane.. That'll get you trying to choose between geoid models. Most boats are airborne or submarines if you ask the gps on wgs84.

agree usually faster,better fix on water or prairie. I have drifted into dark coves at night with a pikepole feeling for steep shore and have found gps to be pretty darn good
For the Geoid correction you will need fine tuned gravity models. Do exist but as we are on the surface not that big issue.
Vertical precision is aprox. the double of horizontal precision. Or 2 times the error.
__________________
bcn is offline   Reply With Quote
Old 27-08-2015, 11:37   #43
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
Re: GPS accuracy

Quote:
Originally Posted by bcn View Post
Yes, a combined Inertial/GNSS IMU will give a quite precise and high bandwidth solution.

Positioning will not be better than the specs of the GPS - so depending on the type of receiver and differential corrections but you can get rid of those spikes of the GPS shown on the screen shots = 3m bare/ 1.80m WAAS/ < 1m with differential corrections in real time.
And you will get a very good heading signal.
Not a inexpensive solution though...

Hubert
We are talking of two possibly similar takes, what I meant exactly is a mixed GLONASS/GPS or a mixed GLONASS/BEIDOU (GLONASS/BEIDOU/GPS, etc.) method.

I do not see where they get expensive. My sub-USD100 does it as well as a handful of brand devices from say Garmin, etc. (e.g. Garmin etrex10)

For a standalone (one gnss based, not a combined signal positioning system) positioning MAY be better, depending on where you are and how the other two systems develop (soon: three other systems, when Galileo will (?) become available).

As you noted: today positioning seems on pair with the spikes removed. I think the spikes are of minor importance anyways when smoothing algorithms are employed (which is the case with gps anyways).

b.
__________________
barnakiel is offline   Reply With Quote
Old 27-08-2015, 12:22   #44
bcn
Registered User

Join Date: May 2011
Location: underway whenever possible
Boat: Rangeboat 39
Posts: 2,752
Re: GPS accuracy

The receivers that can take several GNSS systems (GPS, GLONASS, Beidou, one day Galileo) are not improving precision so much. You have more satellites in favorable positions and thus a more stable reception and less spikes.
This helps especially in complicated locations like cities or roads with a some vegetation. Or in a fjord.
GPS + GLONASS is already a widespread feature in modern chip sets.

People promoting Galileo expect improved precision using the additional L5 frequency. We shall see...

Don't expect the same performance for a GNSS sensor as from a combined inertial/GNSS IMU.
__________________
bcn is offline   Reply With Quote
Old 28-08-2015, 22:44   #45
Senior Cruiser

Cruisers Forum Supporter

Join Date: May 2013
Location: Oregon to Alaska
Boat: Wheeler Shipyard 83' ex USCG
Posts: 1,699
Re: GPS accuracy

From the point of view of an old sailor that crossed many oceans, many times with a sextant. On a ship in mild weather with a 3 star fix, I was lucky to plot a triangle with sides less than a mile.
GPS isn't perfect, but neither are your charts. Most charts are based on old manual inputs. Sighting positions were probably off more than 15 meters. The field people didn't have anything as accurate as gps until recently.
Be happy with what you've got.
__________________

__________________
Lepke is offline   Reply With Quote
Reply

Tags
gps

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Chart Accuracy and Detail Comparison r.fairman OpenCPN 15 20-01-2012 12:39
Accuracy of Passage Weather ? Sabbatical II Seamanship & Boat Handling 7 11-01-2012 16:30
iPad vs Garmin - Accuracy ? Username33 Marine Electronics 3 13-08-2011 19:32
Acceptable Accuracy in Celestial Navigation sneuman Navigation 43 02-02-2011 19:45
Astronav. Instrument accuracy and other meanderings. skookum Navigation 13 15-03-2009 11:03



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 20:23.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.