3D CAD Modelling Types

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HeadingThe development of 3D modelling software enables architects and design engineers to create realistic 3D models of their designs.

Previously they would have been built from clay, card or polystyrene blocks.

A 3D computer model is a virtual object which can be rotated on screen and viewed from any angle.

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The wireframe model is built

up using a series of

connected lines to

produce a 3D object.

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The surface model is built up by drawing the surfaces of an object. Like

adding the canvass onto the frame of a

tent.

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The solid model is built up by using simple geometric

forms or extrusions - such as cuboids, cylinders & prisms.

These can be added or

subtracted to produce complex

3D models.

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Can be produced very quickly.

Can be modified very easily.

Easily add colour & surface texture.

Test structural designs before building eg bridges & skyscrapers.

Easily sent by email to remote locations throughout the world.

Less storage space required than a ‘real’ model.

Used to create realistic simulations.

Clients can explore virtual ‘walk through’ of 3D model designs.

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Computer generated models are virtual and can lack the feel of a traditional model which can

be picked up and handled.

Purchase cost of computers and software.

Training of staff in use of software.

Maintenance of IT systems & network servers.

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3D Clipping& Viewing

process

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Y axis+1

-1

-Z-1

Back Clipping Plane z=-1Front Clipping Plane

y=z

y=-z3-D Extension of 2-D Cohen-Sutherland Algorithm,

Outcode of six bits. A bit is true (1) when theappropriate condition is satisfied

Bit 1 - Point is above view volume y > -zBit 2 - Point is below view volume y < zBit 3 - Point is right of view volume x > -zBit 4 - Point is left of view volume x < zBit 5 - Point is behind view volume z < -1Bit 6 - Point is in front of view volume z > zmin

3D Cohen-Sutherland Algorithm

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• A line is trivially accepted if both endpoints have a code of all zeros.

• A line is trivially rejected if the bit-by-bit logical AND of the codes is not all zeros.

• Otherwise Calculate intersections.

On the y = z plane from parametric equation of the line:y0 + t( y - y ) = z + t( z - z0)

Solve for t and calculate x and y. Already know z = y

3D Cohen-Sutherland Algorithm

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3D Cohen-Sutherland Algorithm

• If t not between [0, 1], then the intersection in not between P0 and P1– t = (z0-y0)/[(y1 – y0)-(z1-z0)]

• If t between [0, 1], then use t to find x and y– x = x0 + [(x1 – x0)(z0-y0)]/[(y1-y0)-(z1-z0)]– y = y0 + [(y1 – y0)(z0-y0)]/[(y1-y0)-(z1-z0)]

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