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Detecting orthagonal viewports

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mr_nick:
Can anyone give me a pointer as to the best way to accurately detect any viewports on a drawing sheet that are displaying orthagonal views? DXF 79 is supposed to indicate this but I have found the results to be very flakey. Creating a brand new VP, it displays as TOP but if I get the DXF 79 value it shows up as 0 meaning it is non-orthagonal. I have to manually change the VP to TOP before it reports the proper DXF 79 value. Also, if I have  a VP which is set to TOP but has had a DVIEW twist applied then the value reverts to 0 meaning non-ortho.

Is there a combination of DXF codes that I should search for or is there a more reliable method altogether?

Thanks in advance.

Lee Mac:
How about checking the direction vector of the Viewport, (Direction Property / DXF 16), e.g.


--- Code - Auto/Visual Lisp: ---(defun orthovport-p ( ent )    (        (lambda ( v )            (or                (equal '(0.0 0.0 0.0) (v^v v '(1.0 0.0 0.0)) 1e-14)                (equal '(0.0 0.0 0.0) (v^v v '(0.0 1.0 0.0)) 1e-14)                (equal '(0.0 0.0 0.0) (v^v v '(0.0 0.0 1.0)) 1e-14)            )        )        (cdr (assoc 16 (entget ent)))    )) ;; Vector Cross Product  -  Lee Mac;; Args: u,v - vectors in R^3 (defun v^v ( u v )    (list        (- (* (cadr u) (caddr v)) (* (cadr v) (caddr u)))        (- (* (car  v) (caddr u)) (* (car  u) (caddr v)))        (- (* (car  u) (cadr  v)) (* (car  v) (cadr  u)))    )) 

mr_nick:
Hmm. DXF 16 had actually been my first approach but I dismissed it when something didn't quite work the way it was supposed to - but I can't for the life of me recall what it was. I have tried your code on a number of drawings I'd previously used my original code on and it's working like a charm so I'm guessing that I had made a schoolboy error - I have to admit my code was far less well thought out.

Thanks for code Lee, much appreciated.

Lee Mac:
You're very welcome mr_nick, happy to be of assistance  :-)

mr_nick:
I've just rediscovered what the problem was with this approach. If I have a view set up that is showing a section taken at an angle through a building, while the view is not orthagonal because it is not truly squared, it is most definitely not an isometric view as the section is taken through the same Z-plane so not looking up/down at an angle. So I guess my question should have been more along the lines of how do I determine if a VP is displaying a 'true' isometric view?

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