Thread: Sonar Quiz #34

Originally Posted by rnvinc

So now ... Does anyone want to take a shot as to why the Humminbird chart screen rotates crazily at lower boat speeds on the Chart Orientation setting of "Heading Up" or "Course Up" ...??

Rickie

The HB Chart Orientation being drawn on the Chart view Defaults to North Up anytime the unit cannot calculate "Course" (remember Course is the direction the vessel is moving) ...

"Course" is a calculation (in the HB unit) between successive GPS data samples (taken from the satellites) to determine if the vessel (on the Earth) has moved from the previous GPS data sample (received by the GPS antenna) to the next successive GPS data sample (received by the GPS antenna) ...

Example ...: GPS data sample 1 has a latitude/longitude of "N xx W xx" ... The very next GPS data sample has a different latitude/longitude showing the vessel has moved "X" number of feet from the position of GPS data sample 1 = and thus calculates the vessel has moved in that direction (and plots onto the Chart view the boat icon as "Course moving in that calculated direction) ...

Due to the inaccuracy of the the GPS system (spec-ed at 8-10meters 95% of the time) - when the vessel doesn't move far enough in a certain amount of time (think less than 0.6mph) = the HB unit cannot calculate "Course" ... resulting in the unit re-drawing the boat icon (boat icon indicating Course can be calculated) into a circle (circle indicating Course cannot be calculated) ...

If the HB Chart Orientation setting is set to "Course Up" - and the vessel is moving fast enough = "Course" can continually be calculated from the successive GPS data samples - and the unit keeps the the Chart Orientation drawn on the display as the user selected Course Up ... meaning "Course (the direction the vessel is moving) is at the top of the screen ...

When the vessel slows down (think less than 0.6mph again) - and the unit cannot calculate Course = the unit Defaults the map orientation on the display to "Default North Up" ...

Thus = every time the vessel slows below 0.6mph Chart Orientation drawn on the Chart view Defaults to North Up ...

And every time the vessel speed up past 0.6mph Chart Orientation drawn on the Chart view reverts to the user selected setting of "Course Up" ...
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Setting the HB Chart Orientation selection to "North Up" keeps the map drawn as "North at the top of the screen" - regardless if Course can be calculated or not ...

The boat icon still changes to a circle at below 0.6mph (meaning Course cannot be calculated) = but the Chart no longer will spin with the Chart Orientation selection set at "North Up" ...

Rickie