Hi Tim / Ryan,

Im testing exporting STEP into Rhino just recently...I have a coupla issues

1) My units are mm (3 dec plcs) in VC but when I import the file into Rhino I get told that the STEP units are Inches :eek:.

2) After the above takes place...Rhino gives me the option to scale the geometry by 25.4, if I do that the geometry sizes are slightly different :eek:

VC size is 25.8 x 53.051 x 31.892mm
After imported in Rhino 25.818 x 53.069 x 31.904

Any ideas how this is happening guys & how it can be avoided!

Hello Paul

Not sure what's causing the problem for you but I can't repeat. When I export your file as STEP and then import into Rhino the component is identical. See enclosed screen grabs. If you would like to discuss further feel free to give me a call or email.

All the best
Nick

Okay spent another 5mins checking and seemingly Rhino doesn't like the corner fillets created by setback....if you look closely there are issues with those surfaces..there are not made that well in VC.

You can see what I mean better by using analyze>bounding box

The planar surfaces report the correct size cube of 100mm. Im still uncertain why VC exports everything in inches when im working in metric ?

Pls advise someone.

I disagree, the unit of the file exported from VC be it STEP or IGES should always match that of the original file unless as you say there are options when being exported.

The Rhino issue is OT therefore I will reply off the forum. A quick note - I would suggest you try to obtain the size of the solid in Rhino using BBox then you will see the size descrepency......

Paul, from experience, STEP isn't that a brilliant format as it once should have been. A shame, but unfortunately true. IGES isn't that much cop either IMO.

Not sure what you mean exactly Tom. My issue is not with the format or the output really but instead the units at which VC exports. You see I work in mm and I expect my software to export in the same format as I model...VC does not ?

I hope we can have the provision to maintain units at export level soon:rolleyes:

It could just be that America's still gripped by inches?! :rolleyes:

STEP is a French invention if I'm not mistaken- so originally it would have been in mm? Have you tried OBJ files? They're good :)

>>Im still uncertain why VC exports everything in inches
>>when im working in metric ?

STEP is a pretty good format and well accepted in the precision CAD community. In the international standards world, it replaced IGES and includes more up to date definitions for solids as well as manufacturing data. IE IGES has issues with mated/coincident faces.

Unlike DXF/DWG, STEP requires the exporting app specify the unit format of the data within the file. It is up to the receiving system to transform the specified format into the one best suited for the receiving system.

Each CAD system chooses their own native unit format. Typically the users are not even aware what the developer has chosen for their native data representation. I'm familiar with major cad systems choosing inches, mm, and even meters.

I have been grilled for years by Spatial not to transform spline data unless it is absolutely necessary. Since our native data definitions are in inches, we export STEP files in our native format to preserve the most accuracy of the data. As such, we have no plans of adding a drop down unit to STEP. We leave it to the receiving system to best choose any conversions of data.


Some more notes:
---Precision and transforms are a huge deal with a solid modeling kernel. It makes or breaks commands from working, especially nearly tangent spline faces in booleans and blending.

---ACIS keeps all data localized around the origin. A transform is added on top of the localized data to position it. Operations such as intersectors are performed on the local data to eliminate error build up related to transforms.

--When you change units in Shark/VC, no underlying geometry data is changed. Unit handling is a post process before strings are displayed to the screen.


Hope that helps!


Tim

Hi Nick,

I was looking further at this, as I am now curious. From the output of step from VC I do see the problems (but have only looked at a cube with 3 adjoining edges with rad/setback). But if I convert the model to mesh within VC and then go over the model in VC to look for any point outside the box, then I see no problem. I did convert to mesh and made output to step, but that file gave errors when attempting to import to other cad, and VC would not re-load that step file.

So I am not sure as to where/what the problem is.


- Steve