An A class surface in the car industry for example is an exterior panel i.e. your door panels, fascias, hood, wing etc.
It is still a 3D CAD model and many packages can be used i.e CATIA etc..
The difference between a Class A surface and say a surfaced model for a hood inner panel is that the surface is much more defined for Class A. The Design Studio are always involved in buying off a class A surface because it is what the customer sees as opposed to a Hood inner (appearance is not much of a concern).
'A' class surfaces will be subject to things like Reflex which is where they will simulate light shining on the surface to make sure there are no imperfections in the surface. They may tweak the surface by tenths of millimeters to get the reflex correct. They will make sure all adjacent surfaces are tangent to each other to get rid of hard lines. They will normally use conics instead of fillet rads to get rid of hard lines at radii. For plastic A surface parts you would be required to show where the parting lines would be as well to make sure they are not going to be objectionable.
Many people can surface a model, good A Class surfacers are much rarer as it is much more skilled.
To add to my last comment, although a bumper fascia would be an A class surface, it could have A, B and C surfaces called out on it for surface definition once in manufacture. These would be used to describe surface quality for paint etc.. i.e on an A surface no paint sags may be present where on a C surface you may be allowed 1 up to 10mm long. A B surface may be the fog lamp pocket etc... B or C surfaces would normally be out of the normal sight line which may be defined as something like 15 feet back and 6 ft up or whatever the standard is for who you are working for. The surface definitions for this will normally be defined by the concencus of Engineering, the Plant, Quality and the Supplier.
A_class surface means - it is not just seen surface and unseen surface In normal no technical words, A_class surface means It is smooth looking reflective surface with no distortion of light highlites, which moves in a smooth uniform designer intended formations.
when you create - car body panel, due to their complex shapes it not possible to create the surface with one single face /patch so you make multiple face/patch ( surface is a group of face/patch added together.)
when these things are added, at the boundary of joining you need to have connectivity and continuation of minimum order two. for example
In case one, at the connecting boundary of two patches you have common boundary but it is sharp corner. this does not qualify as A_class surface.
In case two - at the connecting boundary of two patches have common boundary and no sharp corner - but you have tangent continuity, this also does not qualify as A_class surface.
In case two - at the connecting boundary of two patches have common boundary and no sharp corner - you have tangent continuity and curveture continuity this does qualify as A_class surface. ( ps: sine curve is good example for curveture continuity. but you can not call it a A_class surface ) reason is very simple the real requirement of asthetic and good looking and designer intended shape is not there.
As for as different S/W showing the cuveture continuity in the surfaces. it works like this
If you create a normal to the tangent line on a point which is lying on a common boundary of both patch or face, the variation in the curvature value between the two normal, should not be more than the threshold value which is set as preference value by the S/W ( Normal is nothing but the curveture value of the face /curve at that point ) as for as S/W are concerned
Yes ICEM and Imageware can help you create surface with cuvature continuity, but It is you, who are going to make A_class .
Dassaults Systems has one S/W which was previously owned by MATRA and Cisigraph called "Styler " ( old name was STRIM) , which is supposed to be one of the oldest and very good S/W's for reconstructing the surface from digitised data. |
发表于 2004-12-13 08:16:33
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