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  New Chart Plotters Compared to Older NORTHSTAR

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Author Topic:   New Chart Plotters Compared to Older NORTHSTAR
jimh posted 05-16-2015 09:34 AM ET (US)   Profile for jimh   Send Email to jimh  
I [am] curious whether the newer chart plotters offer a chart offset. The Northstar 95X units offered a chart offset in the menu. Basically move the cursor to where your boat's position should be relative to the chart and set the offset. I found this useful for a creek that I traveled through for every trip, and often that was done at night and in fog.
jimh posted 05-16-2015 12:59 PM ET (US)     Profile for jimh  Send Email to jimh     
In the device you refer to, was the offset applied to the position deduced by the GNSS receiver? Or was it applied to the chart data?

I have a first-generation Lowrance HDS chart plotter. As far as I know, it has no similar feature.

porthole2 posted 05-16-2015 06:16 PM ET (US)     Profile for porthole2  Send Email to porthole2     
Position left intact, the chart could be shifted to match where your position is relative to a land mass.
For example, I saved two waypoints while in the middle of a bridge passage. Split the difference between the two waypoints and then "moved" the chart to match the center of the bridge over my waypoint.
jimh posted 05-17-2015 07:29 AM ET (US)     Profile for jimh  Send Email to jimh     
That option actually sounds a bit scary. Moving the reference plane of the digital chart could be dangerous. It makes an assumption that every part of the earth covered by the chart is in the wrong location by the same offset. In the case of a channel of a waterway, the channel may have just wandered due to natural changes, while the rest of the earth positions did not.
porthole2 posted 05-18-2015 09:48 AM ET (US)     Profile for porthole2  Send Email to porthole2     
quote:
Moving the reference plane of the digital chart could be dangerous.

So could blindly accepting that the supplied charts are accurately placed on the chart plotter's reference GPS position.
My example was one small area that I traveled through 70-100 times a year, a narrow winding creek. I was not suggesting that people go out and start shifting their charts around. With the Northstar units it was a simple few keystrokes to make the shift - or remove it.

jimh posted 05-19-2015 04:02 PM ET (US)     Profile for jimh  Send Email to jimh     
What basis makes you think your several-generations-old GPS receiver is more accurate than the published charts?

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