Error: There is a significant difference between the Initial and Optimized Focal Length - PIX4Dmapper

This article explains and provides solutions to the error caused by a significant difference between the initial and optimized focal length.

Error

Sometimes the optimized internal camera parameters differ considerably from the initial values (e.g., more than 5%).

Description

The software calibrates the camera for every project. The calibration is done during step 1. Initial Processing.

The reason is that the interior camera parameters can vary with temperature, shocks, altitude between each flight, etc.

Cause

The software can read from the EXIF data the focal length and the number of pixels from the sensor (pixel*pixel), but it cannot always read the correct pixel size to calculate the sensor size (mm*mm). This is why the software supposes that the sensor size is 36*24 mm. It supposes that the images have the 35 mm equivalent sensor size. Starting with the initial value of the focal length that is read at the EXIF or given by the user, it recalculates the most appropriate one for the 36*24 mm sensor size.

Solution

1. Edit the camera model using the optimized focal length as it is calculated and process again: How to change the Camera Initial Values to the Optimized Values.
2. If it still fails, look for (on the Internet or ask your camera manufacturer) the real sensor size of the camera. Edit the camera model using the real sensor size and process again: How to use the Editing Camera Model Options.