What happens to the sensor when image size is set to medium or small?

[Saorsa]

I believe the 20m is a "worst case" scenario and I find that in the places I use it accuracy / repeatability tends to be in the ±5m range. Altitude readings are remarkably accurate too; I expect that there must be some kind of link to topographic mapping data.

A former dive buddy is an electrical engineer who did a lot of work in electronic sensor development. He was working on an underwater navigation tracking system and is the one who told me that GPS signals did not penetrate water far. He also mentioned that GPS accuracy could be improved greatly if there was a ground station, at a known location, that transmitted a signal that could be used to correct for GPS satellite positioning errors.

Unfortunately, we lost touch so I have no idea if he ever got his prototype off the ground.

You are thinking about 'differential GPS' which involves a known location groundstation.

[jcuknz]

Further to Manfred #13 ... if you come from the movie world you have been used to framing accurately in the camera and composing [ when you happen to be using a still camera ] for the format it has ... habits die hard and digital is about a fifth of my experience to date .... not to say that I do not enjoy the freedom of digital
It is a useful habit when using inferior formats such as 8mm film or an otherwise highly capable bridge camera ... to shoot what you want rather than the slack [ IMO ] approach of many SLR/DSLR users who waste much of their camera's ability.

[dan marchant]

What happens to the sensor when image size is set to medium or small?

It weeps silently.

[Iconoscope]

All cameras, to the best of my knowledge, use subsampling to achieve a lower resolution rather than pixel averaging. So there is no advantage in terms of image noise or light sensitivity. Averaging or binning pixels would be a definite advantage and is used in some specialized cameras for astrophotography and industrial applications. But it would be great if some manufacturer would make a camera that is capable of binning for consumer or prosumer photographers! The nearest affordable compromise would be to find an older low resolution camera that has a large sensor, like the old Kodak/Nikon DCS series dslrs. My old DCS460 used a sensor with a 1.3X crop factor and was 6 megapixels resolution. Image quality was excellent, but the camera was very large and lacked much in the way of the features found on today's superb cameras.