You’ve all completely missed the point.
I’d never use the published sonar charts
, they are positively dangerous.
When I am using the Navionics tablet app, it saves the depth data that is collected to draw contour lines locally. I don’t care about the contour lines, I have other, better, ways of generating them. What I want is to extract the data from the local files where it is stored… so I can use it in other places.
I COULD save all the data in the nmea
stream, and then filter the depth out but I know the Navionics app has already done this…