Why Face Model in CAD
Exclusive face modeling in Cad requires knowledge of 3D application/s being used. Many people feel that CAD is the best way to model. In CG arch Viz, CAD is the native information you receive from the client. While others feel, the 3D software modeling is more efficient. ADT has a mixture and compatibility of both CAD and 3D. The intent series of tutorials will be to explore this gray area in between.
One must know how to model with faces to effectively clean model in either or both. Therefore, we will start with face modeling basics.
Exclusive Face / Polygon Modeling
An Ornamental Ceiling
We will start by creating a room in ADT, typical of what you might receive from an architect for example. For those metric oriented: Interior wall dimensions based on standard square ceiling grid of 6x6 with a perimeter for an ornamental crown.
Before we, start modeling let us look at face and polygon definitions. A face is typically an area defined by 3 points or vertices. The face will have 3 edges. A polygon is typically an area defined by 2 faces and 4 vertices as a minimum usually 4 sides or boundary type edges. Polygonal Modeling is: primarily the use of quad polys because of the smoothing and editing characteristics, however tri shaped polys are utilized. There are different ways of viewing & controlling a polygon. The most typical is by the boarder or boundary edges, the polygon may have many vertices and thus face edges contained in the area set as defined by the polygon. This is the way, the Max platform, deals with polygons. A 3dface in ADT can be created as a three-sided face or four-sided polygon. Sounds redundant but depending upon how you will use the 3D software it does make a difference. A face can define a mesh, a combination of faces or once again can be part of a polygon that makes up a polygonal mesh. A mesh and polygonal mesh have different inherent display, smoothing, and editing characteristics making the choice of how you model related to how your model will render.
To sum it up, faces are the individual pieces that make up any surface but specifically a mesh surface. Polygonal modeling defines pairs of tri faces primarily as quads (rectangle), then using a tri poly to fill in where needed to close the polygonal mesh.
For our scene, we will be oriented towards polygonal modeling. A four sided 3Dface being used in ADT to create the surfaces. Surfaces have only one side in virtual reality; that is to say, the software only understands them, to have any effect on visibility or light from one side. Yes, you can add a two-sided material, but now the software has to calculate both sides and some like Lightscape gives the surface no understanding except opacity (no light calcs). This surface property is the "normal". Changing it is very easy in the Max platform, not so always so easy on the ADT/Cad non-Viz platform.
• Make sure the UCS II is set to "WORLD" or "TOP" and the view is SW isometric.
• Next, we will create two faces using the 3dface AutoCAD command. The simple way is to just type in "3dface" in the command line or use the drop down menu DRAW>SURFACES> 3D FACE.
• Draw one polygonal face 2'x2' in a clock wise (CW) motion and another counter clock wise (CCW). In ADT, the faces are two sided; the normal however is created by the clockwise counter clockwise motion.
The CCW motion creates the normal facing the viewer of the SW isometric view and backfacing (away) for the CW direction of creation. The normal is only view dependant when the 3Dface is drawn. After that, it will not change unless edited.
It is good practice to always draw in a uniform direction when creating faces for a surface. It is no fun to find a checkerboard of normals when it is time to render.
Now it's time to actually make something.
• Create; 1 new layer called C-tiles-color 30, 1 called C-crown-color 40 and 1 called C-Line-color 24 (Construction Lines).
• Set the C-Line (construction line) layer to current and draw a line or polyline from one top outside corner of the room diagonally to another. The mid point of this line defines the center of the room and where we start the ceiling grid of 3dfaces.
Because we are modeling a ceiling looking down into the room the normals for our surface need to be backfacing from our view and normal to the interior view. So...
• select the 3dface drawn CW, change the faces layer to C-tiles, right click>copy with base point>select upper left vertex as the base point.
• Move the curser out over the diagonal line, right click>paste- the insertion point is the upper left corner, move the curser until the mid point is highlighted and left click to paste.
If you would want the center of the tile on the room’s center, you can use a diagonal line or poly to define the center (copy base point) as we did with the center of the room.
To finish filling in the ceiling grid you can just paste individual tiles as with the first one. Another method would be to fill in 1/4 square, select those nine tiles and use the copy with base point and paste 1/4 quadrant, then half. The array tool is useful, also.
Modeling Slanted Faces
The Ornamental Crown Molding
A fine copper ceiling just does not look right with out an egg and dart crown or rake molding. Again, we will use the 3dface command to create a polygonal mesh.
• Make the USC II world or top. We need end points or vertices for reference and to snap to while creating the faces. The Polar & Object-Snap Drafting Settings on, polar set to 90 degrees or less and the Endpoint selected, snap settings.
• Change the current layer to C-lines, Select the polyline command, and start the poly at the upper inside corner of the room, 8' on the Z-axis.
• After starting the polyline hover the curser over the first endpoint of the ceiling tile-face grid, until the "endpoint" is indicated. Then move inline with the poly start point 0 degrees on the X-axis until the polar position is indicated as Polar: <0 degrees, extension; <270.
• Left click and create a vertex endpoint.
• You can continue on using the Polar and snap or extend the curser and type 24 (inches default on my system), because the next point we need is 24" down the line.
• Continue this around the perimeter of the room and click on the starting point, right click and select close.
Now we have snap references for our copper crown faces. The polyline needs to be moved down so the 3dfaces are pitched somewhat like crown molding. In this case, the molding projects 3" out into the ceiling field and down 3" onto the wall field.
• Select the polyline, you may need to press control and cycle through the possible selections (wall and poly). With the polyline highlighted, hit enter and now it is ready for editing.
• With the polyline selected change the UCS II to front. This gives us a vertical x-y working plane.
• Right click and select move, click on the corner vertices and move the selection down, showing the Polar to be 270 degrees.
• Type 3 (inches) in the command line and hit enter. The polyline is now at 7'9" on the front y-axis and 7'9" on the World Z axis.
• With the polyline selected, right click and select properties. The elevation data entry shows 7'9" (world UCS). You can also change the elevation of an object here by highlighting the measurement and typing in a new measurement (z Axis Coordinate).
|Now create the crown molding faces.
• Change the current layer to C-crown.
• Use the 3dface command and connect the dots, endpoints. Each face should match a ceiling tile as a rectangle. The exception being the corner faces, as these will be trapezoids.
• Use the creation direction based on the SW view. They will all be backfacing or the normal is oriented into the room at a 45-degree angle.
A few words about mapping... The ceiling tiles can be a single image applied to each polygonal face. The crown molding because of the trapezoid shape will distort the image map to fit it's shape or other ugly things. It would be wise to put each wall's crown molding on a separate layer and label north, east.... Alternatively, create blocks by wall. This allows the use of plane based UVW mapping, rotating the UVW plane (gizmo max) to align with the face and adjustments of fit & repeat. Creating layers or blocks allows each to be properly mapped as opposed to having all four face meshes as one object, plane will project only on to face meshes and 90 degrees and the box does project poorly.
When importing using layers to define objects you do not want to weld vertices in max for this type of mapping to individual faces. Although in this case, a tiling map will work just fine for both the crown and ceiling tiles.
The final render of ceiling in max.
Render Of The Work
MAX6 & Mental Ray
We are not going in depth, at this time, about importing into 3D software. Quick explanation of the rendering... Imported into max- layers to entity, no welding- ceiling tile UVW map face image for bump / displacement only- Crown edited into 4 separate objects, UVW plane image (tiled) mapping for bump / displacement only- MR GI; photon & FG
As you can see, Modeling in AutoCAD can produce the same results as modeling in the max platform. For those of us "Drafting Orientated" we can quickly and inherently model for specific image aspects (dimensions). Or, even jump into PhotoShop and create a bump images for the polygon aspects used. As was done for these materials.
Not so productive Cad Commands
There are a couple of handy commands in AutoCAD that will make your face modeling life hard.
Rotate; this rotates the material generation direction, so if you are using a directional map and rotate 90 degrees, the orientation of the image will also rotate 90 degrees.
Mirror; Will flip the normals and the material generation direction for mapping left to right, for example.
It will always be best to create and copy faces on the same UCS II orientation. There cannot be enough said about being methodical and very organized. Layers are the key to this in CAD. Even if you do not create objects by layers, a thoughtful layer organization will give you one more method of filtering selections, if your 3D software supports AutoCAD layers.
The next tutorial will go into working in both ADT and Viz/Max. With the basic of basic principles behind us, we can work deeper into the AEC difficulties and solutions in 3D applications.
You must be logged in to post a comment. Login here.