Calibration

One of the challenges of developing LineSmarts is making it work accurately and precisely on a range of devices, the vast majority of which are unavailable for testing during development. Each model of device has a combination of hardware and software components which are unique to that model. Linesmarts must recognise the correct parameters to apply for each model, identify and utilise available sensors, or work without sensors that are missing.

 

The issue of having to make apps work on the very many different Android devices is a common one, but it is particularly acute for LineSmarts because it engages a range a sensors, and needs to reliably produce precise and accurate results. LineSmarts relies on data from the device camera, gyroscope, accelerometers and compass where available. These hardware components have characteristic parameters that need to be known for LineSmarts to work. Also they may be subject to defects which are specific to the individual device, or artifacts which are common to the general device design. By default LineSmarts automatically calibrates using device information recorded by the manufacturer. Generally this default calibration is accurate however in circumstances where incorrect information or device defects result in poor accuracy measurements the user will need to correct or fine tune the calibration. 

 

Before using LineSmarts to peform measurements we recommend users perform validation tests, on each device that LineSmarts is installed on, to confirm that the automatic calibration is delivering accurate results. One simple test it to compare a measurement of a span or dimension using LineSmarts against a measurement made by an alternative method. If the automatic calibration results are not accurate we recommend that users directly adjust the Fx and Fy calibration parameters.

 

The Fx and Fy parameters can be accessed under the Camera parameters menu, which in turn is accessed from the Settings menu on the Photos page. Predominently adjustment of Fx affects height measurement and Fy affects span measurement but they can both have an influence so we recommend adjusting Fx and Fy at the same time. Increasing the Fx and Fy parameters will, approximately proportionally, decrease the heights or span distances measured by LineSmarts and reducing Fx and Fy does the opposite. So for example if LineSmarts was found on average to be underestimating the span length by 10% the Fx and Fy value should be decreased by 10%. Iterative adjustments may need to be made to achieve the desired accuracy using this method. This process is described in the folowing video: