The reasoning as to why there is not a simple shift in the X,Y and Z is due to a number of factors. The main being that the GPS and IMU sensors on-board the autopilot are not sensitive and accurate enough. An uncorrected GPS will never give results below a meter in accuracy, while the IMU needs to be perfectly aligned with the camera. Then there is the time delay between when an event is recorded and when the image is finally recorded after the delay of signal, light metering and focus lag. For an aircraft travelling at 15m/s, a shutter lag of only 500ms means that the camera will have already travelled 7.5m before it is recorded. Then there are the internal optics of camera lenses to consider that are not perfectly aligned and can distort the final model.
The implications of not using control for othometric surveys is severe. Having only the data sheet from the photogrammetric software saying that, locally, the model is accurate, may be far from the truth on the ground (where it matters). This data has to be confirmed and quantified by other methods as sensitivity and accuracy of on-board sensors is not sufficient.
As previously mentioned, the scaling of a model as 1% over 1000m is10m and is acceptable for certain types of survey. When combined with the vertical element, the variance is not so predictable. For calculating slopes, volumes and gradients, having such a large data range (9%) is far too much for any accurate estimates.
Volumetric work for instance requires accurate and consistent heighting. To accurately determine a volume, a base layer needs to be determined. After earthworks, the area is resurvey using the same datum and the models are subtracted from eachother to determine a volume. Having no control causes errors and uncertainties as the datums will be different for each survey and that we have identified uncertainty within the model.
This is not to say that the data is useless. There may be instances where this data is acceptable such as the beginning stages of land use planning or basic modelling. Often it does not make financial sense to include ground control for simply an orthophoto of a site. In these cases, the data is perfect as it is, but it cannot be transformed into a more accurate rendering of the terrain.
It is expected that in the future, more robust and accurate sensors will be available to surveyors. These are already making their way to market with higher frequency GPS chips that can be post processed to centimetre level, accurately timed IMU sensors and event triggering timers for cameras. It will be a question of time before placing control before an aerial survey is done, becomes redundant.
In conclusion, it is irresponsible of a surveyor to not include control with their survey when undertaking quantifiable work. The uncertainty of the data issued can cause the client to make costly mistakes when doing earthworks or other quantity