autofocus

[jan]

Hello Dmitry,

When building a 3D model from photos which are taken from about 1.2 m from above a horizontal flat object,

the flat object doesn't appear flat when using camera calibrated parameters in photoscan.

Surprisingly, sometimes photoscan produces a flat model with default uncalibrated camera parameters, but not always.

I have also photographs from a great height (>50m) and than the model is realistic when inputing calibrated camera parameters.

Is it possible that these biased models have something to do with the autofocus of the camera when photographing close objects, as the focus is set on infinity when I photographed from great heights.

Is it possible to acquire a realistic model when photographing an object from about 1 meter ?

Thank you,
Jan.

[jan]

In short:

Is it a problem for Photoscan that the camera will autofocus at short distances, and that the focus will not be fixed on infinity?

[Dmitry Semyonov]

Hello Jan,

PhotoScan can process photos with focus at short distances equally well as photos with focus at infinity. However the lens calibration parameters may slightly vary depending on the focus distance.

There may be several reasons of accuracy mismatch you are observing:

• Aerial photos usually have much more texture details than ground based ones. This usually helps to get higher alignment and calibration accuracy as the number of matches across the photos is also much higher.
• Absolutely flat objects may result in unstable alignment results. Even slight relief on the object surface may help to obtain higher alignment accuracy.

With best regards,
Dmitry Semyonov
AgiSoft LLC