Modelling space size?

So...how big is the part modelling space actually in SW04? I can't draw a
rectangle sketch that is 900 m x 900 m. Is this something to do with my
own settings like units etc. or is it really that small?

 

SW has a size limitation - I think for a part it is 1000m either side of
origin (total 2000m) and an assmbly is 500m either side of origin (total
1000m) or maybe it's the other way around?

Merry

 

I can draw a circle with 900 m diameter, but not rectangle that is 900 m x
900 m, strange.

 

Sounds correct, can do D900m circle, but not 900x900m rectangle

 

It must be a 1000m Sphere not cube that would make sense because if it could
be a 1000m cube you could potentially have a line as long as 1732 and change
meter line from corner to corner

Corey

 

Now can you make a sketch with a line from corner to corner?

 

you can extrude your square kilometer by 1 micron and have the correct
volume.
My point is, this "limitation" makes sense because MCADs have to be precise
in small dimensions. The format for floating points used in SW is the C
"double" format, which guarantees 15 decimal digits of precision.This means
the largest and smallest dimensions that can be added and still give a
correct result must not have a ratio larger than 1/10E15. If you want to
measure nanometers (1E-9 m) and still have some margin for geometric
operations, you can't allow dimensions much larger than 1E3 m.

Philippe Guglielmetti - www.dynabits.com

 

Other modelers get around this by allowing users to pick the minimum
dimension. If SW allowed me to say that my minimum dimension was one
micrometer, then I could make models with sizes up to 1 km. If I want my
minimum to be 1 mm, then I could go to 1000 km. The downside is that they
would have to figure out how to handle parts that are done to different
minimums. The other guys did it, so I suppose SW could as well.

Jerry Steiger
Tripod Data Systems

 

Wow, amazing what you find out. I always though the environment was
infinate. DOH....learn something new everyday.

 

I knew that there is limit, but I thought that the space is much
bigger..

 

That wasn't actually me...bridge maybe

 

Ok....so lets just say, hypothetically speaking, if you had something
bigger, that had to go together, what would you do? And is there an
environemnt that goes bigger? Would it make sense or even do-able to have an
infiate environment?

 

as I explained earlier in this thread, you can't have a larger world if you
want nanometric precision.
Right, some software let you choose a tradeof between size and precision, SW
doesn't.
But you still can decide to scale your whole model by, say, a factor 1/1000,
or 1/1'000'000. Then you just add a few zeros in your drawing scale...

 

You could scale with meters it is really simple 1CM = 1M then you could fit
a model that is 100 times bigger per-say. Then if you already have modeled
other parts that fit @ normal scale that need to be in an assembly you can
make a 1/100 scaled config.

Is the Assembly space constrained by this same 1000 meters?

Corey

 

you can make a circle 1000m dia. and a square 707.10678119 a side

 

64 bits processors can handle 64 bits integers (you don't often use numbers
larger than 4 billions, do you?), but floating point numbers used in SW and
most (all?) other cads are already 64 bits "double-precision" (see
http://www.intel.com/technology/itj/q41999/articles/art_6.htm, page 3) that
have a mantissa of 53 bits.
As I explained earlier in this thread, the double format
"
guarantees 15 decimal digits of precision.This means
the largest and smallest dimensions that can be added and still give a
correct result must not have a ratio larger than 1/10E15. If you want to
measure nanometers (1E-9 m) and still have some margin for geometric
operations, you can't allow dimensions much larger than 1E3 m
"
By using the "double-extended" format (80 bits, 64 bits mantissa), you could
reach 18 digits of precision, which is the maximum "floating point units" of
current processors (32 and 64 bits) can handle. As you can see on intel's
page, their processors use an internal representation with a larger
exponent, but the mantissa is max. 64 bits.

Bignums are handled as string (usally in coded in BCD, with one decimal
digit coded on 4 bits, so 2 per byte). They are fun, but definitely not fast
enough for interactive applications

 

Since you all brought the subject of units, I have a question. First
some background; I am considering purchasing Solidworks, after we had
a failed effort to incorporated Inventor into our design process. One
of the minor hassles I ran into with Inventor were limitations and
inconsistancies when using feet-inch units. Eventually I realized
that this was because Inventor was purely metric, even when the chosen
units were feet-inch. The hassles were simply the result of the
metric-mindedness of the program.

Is Solidworks also purely metric internally (i.e. all units are
converted to metric for the internal drawing database)? Are there
hassles I should expect for using Solidworks for an industry which is
purely feet-inch?

[By the way, I have significant doubts the U.S. will ever totally
convert to metric.]

Joe Dunfee

 

The only dificulty I have run into is when using API. It is a simple
conversion though. I have never noticed a problem, we work solely in
Inches. Could you describe the problems you ran into, I will be sure to
watch for similar behavior.

Corey

 

The problems I ran across in Inventor were mostly in the sketch
creation. Regardless of the units you choose as default, it always
showed a decimal version. (though it accepted and then converted most
any unit you typed in) If you wanted feet-inch, it would show decimal
feet. There were a few other areas where it was inconsistant, but I
don't recall them now.

I think CAD programs should always be unitless internally. That
way, it wouldn't matter if you want to work in angstroms, wavelengths,
inches, meters, or lightyears.

Joe Dunfee