Inversion

[RCA]

Actually precision is not more credible when mixed measures are used and you are measuring differently in the upper level than the lower level because you cannot physically measure the exterior of a half story unless you are a lot more agile than I. Further, if you ask me, ANSI is suggesting that all dormers are NOT GLA...they are too narrow. On and on. The precision of assessors drawings vs appraiser's measurements are generally inconsequential. Or as someone else noted, we are fixated on measuring to the tenth, then use a rounded SF adjustment figure to adjust a difference of less than 50 SF in the adjustment grid... Go figure. Inaccurate but precise.

1. Well there is truth to the adage: "If you take care of the small problems, the big problems take care of themselves." As I have already stated in other posts, accuracy allows you, if you are doing both interior and exterior measurements to create checks on your measurements. Interior room measurements + wall thickness = exterior measurements. If you are only measuring to 6-12 inches, you don't have good material to work with. If you measure to 1/100th of a foot or even 1 inch, and your interior and exterior measurements agree, you can be very sure that everything is fairly accurate. If you are creating you floor-plans in some CAD system like Chief Architect - it is doing the reconciliation for you. When you start the plan, you enter the default interior and exterior wall types -from which it gets wall thickness. You then enter exterior and interior measurements. If you enter a measurement which doesn't reconcile - you will get immediate feedback.

2. You can physically measure just about anything with a Leica X4 and DST 360. But to be honest, if I have a split level, I just line up the upper floor edge to a point on the first floor exterior and measure to that. And I will also confirm that through reconciliation.

BTW, the way the DST 360 works is that it has horizontal and vertical angular measurement and levels. You put your X4 laser meter on the DST 360, level the tripod and move it around the building which can be whatever stories high. You point the laser at one corner (using the view window to get it exactly on the corner), and then swivel horizontally to point it to the next corner and push the correct function - and it will give you the distance. It can do this using trigonometry on the vertical and horizontal angles - along with the distances to the corners.

I will iterate that LIDAR is potentially capable of better accuracy some respects, if can get around the problems of low-light and reflection. What is more exiciting about LIDAR though is that it could potentially create a complete CAD plan from exterior and interior scans of a house.

Cubi Casa says it can deal with attics by scanning the ceiling. They also claim to be able to deal with stairs of all types. I haven't tested it myself. I have used "3d Scanner App" which is popular. But I found it to be slow and difficult to use. You can get to the end of the floor and have the whole thing blow up on you - forcing a rescan. Skylights are a big problem, as well as mirrors and dark areas. It is not easy.

 

[Terrel L. Shields]

fairly accurate

Hand grenades are fairly accurate

 

[TerryRohrer]

As with any data source used, it is up to the individual appraiser to make the decision as to what he or she considers reliable.

Heck, I am old enough to remember back when forms software was first introduced and some "old timers" would not convert because they didn't trust forms software to do the math correctly. I fought that battle within my own office

Understood. Although, in fairness to oldtimers, there are some forms in some software where the math remains incorrect!

 

[RCA]

There are 2 common wavelengths of LIDAR - will they work differently? Do we get the SLAR problem (or benefit) of "seeing" deep into walls. beneath canopy, through the trees and dross of every day life. Just asking.

LIDAR is just emitting and bouncing light off surfaces. So, there is no depth perception per see. However, if it sees a flat surface, an obstruction or disruption and the flat surface continuing in the same mathematical plane on the other side of the optical obstruction, then it may assume that beneath the disruptive obstruction the flat wall exists. So, it can infer depth under assumptions about continuity of mathematical planes. In fact, it uses regression to find and define the common geometric structures:

https://core.ac.uk/download/pdf/51406199.pdf

As far as the two wavelengths you mention, you probably mean 905 and 1550nm. Both can damage the eyes, especially the 1550nm, which is used mostly in military grade LIDAR devices. 905nm is used because it is mostly filtered out by the atmosphere in light emitted by the sun. Apple uses LIDAR in the range of 8xx nm (visible red light) - and that can overlap with the Sun's visible red spectrum. So, point your IPhone 12 Pro up towards the top of a house on a sunny day and you can be sure it won't be able to measure anything.