Matching the angle of an earlier photo
Everyone who has tried a progress series has tried to reproduce a shot from memory. It fails for a reason worth understanding: you are trying to match four independent things at once, and the eye is unreliable at three of them.
01
You cannot judge your own distance
Standing "about where I stood" is accurate to maybe half a metre, and half a metre is a visibly different photograph. The only fix is a reference you can see while shooting, not one you remember.
02
Tilt is invisible until it is wrong
A phone a few degrees off vertical stretches or compresses the subject. You cannot feel it in your hand, but you can measure it — the same sensors that rotate your screen know the angle exactly.
03
Overlay beats side-by-side
Two photographs next to each other let you compare after the fact. The old photograph shown faintly over the live camera lets you correct before you press the shutter, which is the only moment the correction is free.
What LAPSE does with this
It holds your reference on screen while you frame, reads the framing with the device's own vision processing and the tilt from its motion sensors, and tells you when you match. All of it on the phone — nothing is uploaded.