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  GPS Receiver and Chart Plotter Zoom in Feature

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Author Topic:   GPS Receiver and Chart Plotter Zoom in Feature
dmeswi posted 07-03-2011 05:22 PM ET (US)   Profile for dmeswi   Send Email to dmeswi  
Sometimes I will go out to a fishing spot on a clear day and I can zoom the GPS receiver and chart plotter in to within 15 yards of the targeted waypoint. I can then pick up the bottom structure on my sonar with no problem.

I may go back to the same spot on a clear day a few days later and the GPS receiver and chart plotter will only zoom to within 400 yards of the targeted waypoint which makes it difficult to find a small piece of structure on the bottom.

Is this a common occurrence? Is something wrong with my Navman Tracker 5500 GPS receiver and chart plotter? Is [variation in ZOOM level in the chart plotter caused by] the [orbital position of the GPS] satellites? Would a different GPS receiver and chart plotter provide better performance?

Dennis

jimh posted 07-03-2011 07:44 PM ET (US)     Profile for jimh  Send Email to jimh     
I don't recall seeing any variation in the limit of the ZOOM function on the chart plotter display on my boat. Perhaps you could contact the manufacturer of your particular device to ask them about it.
Chuck Tribolet posted 07-03-2011 11:12 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Dunno why some days it won't zoom as far. Maybe the zoom in
button is tired. Try zooming back out and back in and see
if it stops zooming at the same scale.

Also, learn to program your GPS to navigate to a waypoint.
That will point with an arrow and tell you how far.


Chuck

K Albus posted 07-04-2011 09:40 PM ET (US)     Profile for K Albus  Send Email to K Albus     
Electronic chart cards are often created with data from both large scale charts (more detailed charts covering a small area) and small scale charts (less detailed charts covering a a large area). If you are in an area covered by a large scale chart, you chart plotter will usually show more detail at a higher zoom level than it would show in an area which is only covered by a small scale chart. If you're getting different maximum zoom levels at different locations, this could explain the difference.
jimh posted 07-05-2011 07:59 AM ET (US)     Profile for jimh  Send Email to jimh     
quote:
Is [variation in ZOOM level in the chart plotter caused by] the [orbital position of the GPS] satellites? Would a different GPS receiver and chart plotter provide better performance?

The precision of a particular position fix deduced by a GPS receiver can vary with the geometry of the satellites used in the sight reduction. However, the GPS receiver just informs the chart plotter of the position. If the chart plotter were going to make an adjustment to its display of the position it seems unlikely that it would adjust the ZOOM level to compensate. If would not be reasonable to limit the ZOOM level based on the current position if, for example, you wished to zoom-in on some other portion of the digital chart. I doubt that there is a correlation between the fix precision due to satellite orbital geometry and the chart plotter ZOOM.

It is very likely that you can get improved performance from a more expensive chart plotter. More expensive chart plotters typically have faster computer processors and can calculate faster. This allows for faster screen redraws, and in general faster overall performance.

GPS receivers can be improved in performance as well, however it is unlikely that a faster or more sophisticated GPS receiver is going to influence your current problem with the ZOOM level.

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