我使用vsfm和注意到的日志，这些日志对我来说不是很容易理解。我仅将vsfm和3D reconstruction用于两个图像（没有exif）。计算匹配和3D reconstruction之后的日志如下：
0: tree3_001
image_size: 1080x1920
1: tree3_005
image_size: 1080x1920
Loading image pixel data ...done in 0s
Run full 3D reconstruction, begin...
1 pairs have two-view models
1 pairs have fundamental matrices
Initialize with tree3_001 and tree3_005
781 3D points initialized from two images
PBA library version = 105
PBA: 781 3D pts, 2 cams and 1562 projs...
PBA: 1,128 -> 0,466 (100 LMs in 0,22sec)
Focal Length : [2304,000]->[1411,135]
Focal Length : [2304,000]->[1437,606]
当我再次进行3D重建时（具有相同图像），与焦距相关的日志不同：
Run full 3D reconstruction, begin...
1 pairs have two-view models
1 pairs have fundamental matrices
Initialize with tree3_001 and tree3_005
846 3D points initialized from two images
PBA library version = 105
PBA: 846 3D pts, 2 cams and 1692 projs...
PBA: 1,130 -> 0,469 (100 LMs in 0,22sec)
Focal Length : [2304,000]->[1602,099]
Focal Length : [2304,000]->[1626,518]
我知道值2304是1.2*max(width, height)的结果，但是第二个值在每次执行中都不同。
谁能帮助我，并解释焦距第二个值的含义（从记录中得出）以及如何计算？