Apologies for this post as it is not to do with mobile phones, but at the moment, there is no place to put this thread ^^
I have a Garmin SatNav which shows a 'Max Speed' of 598mph. This may be correct as the user may have turned the device on while travelling via airplane (jumbo jet by the looks of the speed) but my question is, does anybody know how accurate this information is?
I personally have a Garmin device which states a max speed of 151mph…this is surely not accurate, but my device may be an exception.
I have tried speaking to Garmin but, naturally, mums the word about their testing!
Any opinions will be greatly appreciated!!!
Are you looking at the actual device to tell you this or is it from an analysis? I have a Garmin SatNav so I can tell you if mine is correct if you let me know where to find it! )
I would split the question of 'accuracy' into two parts in this case; Firstly the validity of the measurement (i.e. is the unit capable of correctly calculating this measurement under the defined conditions) and then assuming a valid measurement is possible, what is the accuracy of the measurement result.
validity - This essentially depends on unit design; Whether the GPS measurement core is designed with sufficient calculation/resolution for measurements in this range, for example (verifying the capabilities of the chipset/API used in the device in question would provide an indication). Other issues, such as whether the calculations include any inherent limit to altitude, or the way in which speed is calculated may also be relevant, e.g. if velocity were calculated from every two successive measurement points, it would only take one 'rogue' position calculation to provide an invalid speed result (which could then easily be stored as 'max').
accuracy - Assuming a valid measurement, then accuracy will also depend on a number of factors, including how many satellites were visible at the time, matrix (or linear equation) calculation accuracy etc. One useful measure of this is DOP (Dilution Of Precision) which if you have the actual positional measurements may also be stored alongside each.
Pragmatic tests with the unit/model in question could answer some of the above (whether valid non-surface measurements are possible, increasing speed to known ranges etc); actual calculation details and/or storage of the related position points with DOP accuracy would be ideal for validation of the max speed value.
Phil.