yang Hmmm. There are different things at issue here. First lets accept that buildings don‘t accurately follow the rules of geometry - walls are not pure planes but can be twisted and bowed. At what point do we accept three (or four) points to define a plane and when do we need extra points to define the wall? I suggest that five points are good for 3 m walls, and more are necessary for longer walls.
Measuring a window niche has four side planes and the window itself inside a large wall. The side planes aren‘t too sigificant since then tend towards 90 degrees and are short. The built intention is usually clear. The window itself should be parallel to the main wall. If it is not, then it is „interesting“ because you might want to correct it when replacing the windows and need to deal with the window sill that no longer fits, because it was cut crooked to fit the window.
I think part of the isue needs to be answered with what you are trying to measure. If my job is the replace the windows then I want to know how big the windows are and probably don’t want to know that the window is crooked. As the architect I‘m more interested in knowing that the window is crooked than the exact window dimensions - the window supplier needs the millimeter exact dimensions. I just need accurate enough dimensions to get a price.
If I am honest about what I want, I would like a model of all the planes measured in 3d. You take the camera and detect the planes and then ask the user to laser the key points with the option to ignore things - no need to measure this window if I know I am going to close the opening. For long walls you would target extra points to get an accurate model even if the wall is bowed and twisted. You show the wall with target points on the screen and the user sets the laser on the point and verifies it. As the user moves around this gets complicated but it is easier to ensure that surfaces are measured accurately on all sides. I accept that this is not version 1.0
For V1.0 with just point to point measurements, how about a corner detect function that uses the camera to identify a corner and the laser to verify the corner position. In the case of a window - desired length and width - the camera (AR whatever) sees a corner and generates a grey transparent circle over the corner. This should be an area about 2 cm in diameter. The user lasers the corner and then you correct the start poition to the actual intersection point. The laser measured point is close to the actual corner - from 0 to 1 cm. You improve this with plane detection to get the best start point. The end point is done the same way.
Edges can be done similarly. Detect two planes and measure from the edge. This brings up another „feature“. When measuring edge to edge, I may need to know that both points are at the same height. Could you place a dashed level line in the display so points can be taken at the same height? I can see other uses for this function. First are things level, and second what is the angle of a ceiling relative to a level line. Vertcal lines are equally useful.
Without a tripod I don’t know how accurate you can measure anyway. Both the motion to swing from one corner of a room to the other, and position of the person leave room for error. Comparison measurements with and without tripod will determine if a tripod is always necessary.