A lot depends on the type and magnitude of movement you are trying to observe. A scanner may be the ticket, or it may be massive overkill.
Once you answer those questions do two things.
1. Screw it up exactly the same way every time you observe.
2. Report it in a format meaningful to the client. Most clients have no use for a coordinate table. They need to quantify movement of a structure relative to a feature.
Hope that helps, Tom
What is purpose of monitoring?
has 200yo wall suddenly moved?
does client have structural engineer on board.
Done this exact thing on a newly built overpass that was suspected to be bulging. And yes- it was scanned (this was in 2003!). Every week for 2 months.
We determined it was indeed moving and the whole thing got rebuilt.
Also did movement monitoring on the governor’s mansion after it was nearly burned down about 10 years ago (all kinds of stories about that one). But it was way fewer data points, and we just used targets fastened to different parts of the building, shot conventionally.
As others have said, whatever way you do it you MUST have immovable reference points somewhere.
Depending upon how long between surveys and how much movement is expected, if scanning you might need to sweep off all the leaf clutter which collects between the stones - if the movement is small or intermittent it does make a difference. Stones can "roll" in the wall (see near the trees growing out of it) and leaf clutter can disguise that.
In dry weather the wall might move back as the ground behind dries out - I've had that happen, especially where the top of the wall is leaning back as this one does: then the upper stones might settle rather than move in x,y.
If you put targets on the wall, make sure they can't come off - small paint dots might well do. On the size of the wall shown it isn't going to take long to observe individual points - record in co-ordinate mode, drop into a spreadsheet and the office work is minutes. "Contouring" the face in x,z with y values as the contours will show up what is happening very quickly
