Garmin 196 Calibration

[Guest Cali]

Hi

 

I need some help with my Garmin 196. It seems that the calibration is out. When I use it in "Land" mode (I do not have an aircraft yet:crying:) My track shows anything from 5-100m from the road on the map. Sometimes when I drive on back roads that does not appear on the map, my return trip will not be on the same line.

 

Any help would be much appreciated.

 

Cheers

 

Cali

 

 

[Guest pelorus32]

Hi Cali,

 

a couple of things may be going on here, calibration is likely not one of them.

 

GPS uses the WGS84 datum and geoid from memory. This is an "approximation" of the earth's surface. If the underlying map in the 196 is not WGS84 then the GPS can show errors between the map and your position on it. You have the choice somewhere in the software to change the datum used. You should only do this however if you know what you are doing and if you make sure that you chnage it back for use of the aviation mode.

 

The second issue is that the GPS updates every x seconds. This creates a series of known locations in time. The "track" is therefore a join the dots exercise. At the 196's update rate of 1/sec at 100km/hr that's nearly 28 metres between updates. That can lead to apparent positional errors as update points and turning trends will differ on the outbound and return legs.

 

Your GPS also has varying accuracy depending on how good a satellite fix it has. This can vary depending on the number of satellites in view at any given time. It can also be impacted by parts of the vehicle cutting off the view to certain parts of the sky. This in turn can vary with direction of travel.

 

Further the 196 has a stated positional accuracy (without WAAS) of 15m. This is with an "ideal" fix. So let's say that these errors compound themselves. You are 15m out one way on the outbound, 15m the other way on the inbound, you also have say another 10m of positional error each way because of less than ideal fix and the updates happen to be 28 m apart. Plus the width of the road - a difference of say 8m and you can end up with say 15+10+8+updating error in either direction. The worst case is a position 66 metres or more apart from one fix to the next.

 

The end result is that the track may in reality coincide on the ground to within say 8-10 metres (road width) but position errors inherent in the system can make this difference seem much greater.

 

Regards

 

Mike

 

 

[Guest aircraft1]

VERY GOOD EXPLINATION !!

 

 

[Guest Cali]

Thanks Pelorus32

 

Very good reply:thumb_up:

 

 

[eastmeg2]

Cali,

 

The 296 has an option to lock to nearest road or some thing to that effect. You may find the 196 also has it.

 

 

[Guest Cali]

Thanks Eastmeg2 I will have a look.