by the way someone ( Mignius ) made an SVN with lot’s CAD feature but it is not free !
happy bl
There is… but it’s not a simple thing to do. And it’s not just Blender necessarily. Some of the libraries that Blender depends on make certain assumptions about data and expect the currently low-precision structure.
Even then, it’s still completely different than how many CAD applications work. It’s not just that Blender uses single-precision floating point values… it’s that Blender uses floats. For the sake of precision, a lot of CAD applications don’t use floating point numbers at all… just really big integers. Blender doesn’t do that and it would require a massive effort to make it behave that way.
And note that this precision thing is just one of the fundamental decisions in Blender’s design that make it inappropriate for CAD work. There are more. That doesn’t mean Blender has a bad design… it’s just not an appropriate foundation on which to build proper CAD tools.
can you ask Ideasman to give us a feedback on this
would like to see what he can tell us on this !
did not know that cad use only integers !
does not make sense to me !
thanks
happy bl
How inaccurate can the model be? Is it only sub millimeters or we are talking about bigger numbers?
in architecture we usually work in cm and in some details go to mm but mostly cm
that has been discussed many time in different threads !
but let says that you do some scripting for designing objects
when you work with normal scale resolution is at 0.001 or in metric 1 mm
if you do several math operations you loose precision
python works with 16 digits but internal blender convert to 7 digits
right there this becomes a source of errors / problems
happy bl
you could also move around this problem by making code see 1 m as 1 cm for example. This way you could raise precision very high. That would create problems however for exporting to other apps, but probably would be a case of just scaling the model down to 100 times when it was imported to another app that has much higher precision.
I work with cm and millimeters and have not seen any problem so far inside Blender.
In any case as I said, problems are there to be solved, no problem is a show stopper.
To be honest I move models from blender to autocad on daily basis and no issues there…
This is why I don’t see any problem with dimensioning in blender I just never had an issue with it so I guess in real life use the precision issue is not such a big deal at least for architecture…
also depends on country where you are!
here we work with only mm !
happy bl
Not in Blender, but I did a true model of the solar system in other software, and although I used meters to millimeters, it was all to exact relative scale. Let’s just say the software had huuuuge problems even getting basic shading correct. I can’t recall if it was based on floating point (max 32 bit accuracy at that time) or design cube integers. Probably floats. I can only recall Microstation doing “that weird stuff” 
Hmm, I use sw that used to use (now uses their own) the parasolids kernel (same as Microstation), but I don’t recall ever having to define a working cube.