Way to calibrate GPS?

[Shallowminded]

I am posting this under general GPS but I have new Garmin 440s that I have a question on. Seems like it may apply to all GPS units.

Is it possible to calibrate a GPS? My first day using it shows me about 50 feet North and West (in the marsh grass ) of my actual position. Will it vary from day to day, can I calibrate it, or do I need to adapt to it?

I want to thank everyone on this site - the info available has been a tremendous help getting my boat set up and getting used to the Triumph way of life! And the search function actually works!

Ric

 

[BeeReel]

Most of the error is in the map input data. Some variability is also there due to the map scale being viewed and I've also noticed speed of travel. So guess what I'm saying is get use to it. I have one boat launch that shows no water for the first 100ft of travel. The GPS locates/fixes itself from at least 3 satellites so not sure how one would go about calibrating?

Use a split screen map/sonar to get the most accurate real-time data. Trying to find underwater landmarks: use the map to get in the vacinity and the depth/sonar to pin point.

 

[BarryB]

Make sure WAAS option is activated. GPSs are not as accurate as you may think, that is why Loran is used by fishermen. Loran would put you on the same spot every time.

 

[BeeReel]

Just found these numbers for my Garmin 545s:

GPS Accuracy:
Position: <49 ft. (15 m), 95% typical
Velocity: 0.164 ft./sec 0.05 m/sec steady state
WAA S Accuracy:
Position: <10 ft. (3 m), 95% typical
Velocity: 0.05 m/sec steady state

 

[Shallowminded]

Thanks for the help. I am not sure if my model has a WAAS option but I will check when I get a chance. I am also talking to Garmin for suggestions and they first want me to update my software version to see if it helps. I will post updates when I have new info.

 

[BeeReel]

New Garmin update:

Marine Software Update 5.0

 

[pamarine]

Shallow, yes you have WAAS and it is enabled by default.

As for calibration, no, there is no way to calibrate the GPS.

You will get variations in accuracy based on weather, location, Artificial signal degradation (localised SA), antenna location, etc.

GPS's overall accuracy is far better than Loran, but its repeatability is worse. This means that if you had a Loran-C and a GPS mounted on the same boat, and mark the same location on both. The GPS (with WAAS) will always take you to within 15m of your point (95% of the Time with maximum satellites in view and receiving [which is 8-12], the other 5% is a crap shoot). The Loran will take you to within 1-2m of your spot 99% of the time (natural radio interference phenomena not withstanding).

Both are good enough for the casual user. Where GPS shines is it's reproducable accuracy across multiple receviers. If you take the same Coordinates and put them into your buddy's GPS and his unit will get you back to withing that same 15m (again, 95% of the time). You take your TD's and put them in to your buddy's Loran and you could be a 1/2mi away or more from your intended point or right on top of it, you just never know.

Anyhoo, Hope this Helps.

 

[Shallowminded]

More knowledge always helps!

BTW, for those of you with Garmin 440s, the newest software version is 5.20 (straight from Garmin, just came out).

https://buy.garmin.com/shop/store/downloadsUpdates.jsp?product=010-00515-40&cID=148&pID=8055

I think you have a different model Bee, so yours may or may not be 5.20.

 

[BeeReel]

More knowledge always helps!

BTW, for those of you with Garmin 440s, the newest software version is 5.20 (straight from Garmin, just came out).

https://buy.garmin.com/shop/store/downloadsUpdates.jsp?product=010-00515-40&cID=148&pID=8055

I think you have a different model Bee, so yours may or may not be 5.20.

I have the 545s model. The upgrade is to 5.2 across all models, the link mis-represents that it is 5.0. Make sure you pick the upgrade specific to your unit, the warning states they are all slightly different.

 

[Shallowminded]

The sun was actually shining yesterday (10 inches of rain so far in December) so I finally go out in the boat (45 and windy).

I upgraded the software with no improvement. But... the unit says that the WAAS error is less than 7 feet so I guess I need to adapt my thinking a bit. My expectations were a little unrealistic but it is my first time using one.

Thanks for help!
Ric

 

[pamarine]

The sun was actually shining yesterday (10 inches of rain so far in December) so I finally go out in the boat (45 and windy).

I upgraded the software with no improvement. But... the unit says that the WAAS error is less than 7 feet so I guess I need to adapt my thinking a bit. My expectations were a little unrealistic but it is my first time using one.

Thanks for help!
Ric

As long as you can cast longer than the error distance you should be good