Thanks for the reply SAV,
Both GSD and Spacial Resolution are purely theoretical numbers. And while they are useful to a degree, it's like judging a photograph purely based on the megapixels the sensors. We all know there's more to how sharp an image is, then just the sensor.
To measure the ability of a camera/lens combination to capture data, charts like these are used to determine the resolution of the lens/sensor combination. Change the lens, and the captured chart will show different results (more or less resolution depending if the lens is able to resolve more or less detail)
(http://www.imaging.org/site/images/IST_Images/Standards/Resolution%20Tool%20Images/ISO12233-2000_chart.jpg)
Camera resolution test chart from ISO 12233:2000
Similarly in photogrammetry, the lens plays a HUGE part in the resolution the camera can capture, which is why I called GSD and Spacial Resolution purely theoretical. Depending on what lens is used (and how the entire system is used) you can get closer or further to that theoretical number.
Would I be wrong to assume that there's no standardized method to measure Actual Spacial Resolution (not theoretical) with some sort of equipment similar to what the chart above does for photography?