Digging Deeper into Materials (Circles and Lines AutoCAD Tutorial)

28 Feb, 2007 By: Lynn Allen

Customize materials to get the look you want.

Last month, we dipped our big toe into the world of materials. This month, we'll go just a bit further (perhaps up to our knees?) and explore materials further. If you need to catch up, click here to review last month's column.

Though AutoCAD 2007 ships with more than 300 materials, a fairly hefty number, you still may not be entirely happy with your options. Realizing that 300 materials doesn't cover the entire spectrum, AutoCAD provides the ability to customize materials to get the exact look you are after (or at least to get close).

You can create materials from scratch -- but it isn't pretty and it's time-consuming. So, unless you get paid by the hour, you're better off taking a material that is relatively close to what you want and customizing it to get the desired results.

Step-by-Step Material Update

You can find the Materials tool in the Materials control panel on the Dashboard.
To begin, open up your Tool palette and peruse the Materials or Materials Library palettes. If they don't display, right-click on the Tool palette bar and select either Materials or Materials Library. Here you'll find all kinds of possibilities.

You can also open up the Materials palette by typing in MAT or by selecting the Materials tool from the dashboard.

Select a material you'd like to work with from the Tool palette and drop it onto the top portion of the palette. This material is added to the list of loaded materials in your drawing.

Use the Material palette to customize your materials.

A material is defined by a number of qualities. The qualities available for customizing depend on the template assigned to the material. The four templates (found in the drop-down list) are: realistic, realistic metal, advanced and advanced metal.

Realistic and realistic metal. Materials are based on physical qualities.

Advanced and advanced metal. Materials allow more options and the ability to create special effects such as reflections.

Diffuse color. Of course, the most basic quality of a material is its color. The Diffuse color option controls the main color of the material. If you find a material that is exactly what you want but the wrong color, select the Diffuse color swatch to open up the Select Color dialog box. If the material has a texture assigned, and you find that the color hasn't changed, you may need to do additional work. Locate the Diffuse map section on the lower half of the dialog box and drag the slider bar slightly to the left (somewhere between 80 and 85). Don't pull the slider too far to the left or you start to lose the detail in your texture as the color begins to take over.

If this doesn't give you the color you're after, return to the Select Color dialog box and kick the color up a few notches by selecting an exaggerated hue of the desired color. For example, if you want a medium red, select a very bright red with a high saturation level instead. This may take a little testing, but eventually you should be able to get the color you're after.

When you select an Advanced Template, you'll see two additional color options, Ambient and Specular. Ambient is the color that appears on faces when only ambient lights are used in your drawing. Specular controls the color of the highlight on shiny materials. Highlights, of course, are always lighter than the diffuse color.

Shininess. Drag the slider bar to control the shininess of a material. Shiny surfaces have a small highlight and rougher materials have large highlights.

Translucency. An object that is translucent transmits light, and the light also scatters inside of the object (think of frosted glass). Drag the slider bar to the right to make the material more translucent (this ability is not available for metal templates).

Self-illumination. This option allows you to illuminate an object from within so that it emits light (although this light isn't cast onto other objects). This property also isn't available for metal templates.

Refraction. If a material is translucent, rays of light are bent as they pass through the materials. This distorts any objects that are seen through the material. A refraction value of 1 doesn't distort hidden objects, but a value of 2 distorts the objects greatly. This ability also isn't available for those poor, neglected metal templates. A few examples of real-world refraction values: air has an index of refraction value of approximately 1 (a vacuum ranks as a perfect 1), glass rates somewhere between 1.5 and 1.7 and a diamond is roughly 2.4.

Texture. If you want your material to look truly realistic, you should add a texture (or bitmap) to it. You can scale, tile and rotate the map you add to a material to suit your needs. You can use the following file types as texture maps: BMP, GIF, JPG, PCX, PNG, TGA and TIFF. You can get really clever with bitmaps, even applying pictures taken with your camera as textures. You can also apply more than one map to the same material until you get just the result you desire.

Use a combination of maps to get the exact desired texture.

Bump maps create an embossed effect on a surface and add depth to your material and realism to your scenes. (They also slow down the rendering process but are worth it!)

Reflection maps use an environment map to simulate a scene reflected on a shiny object. One of the most famous reflection maps was that of the 1994 black Miata (top down, of course) owned by George Hudetz used in Autodesk Inventor (as seen below). For years, people asked me what kind of car that was! To get proper rendering results, you must make sure the material is shiny, and the bitmap should have a high resolution (at least 512x480 pixels).

Use a reflective bitmap to add realism to your models.

Last but not least, opacity maps are used to specify areas of opacity and transparency. The AutoCAD Help file has a good description of this function that I'll borrow: "If you have a black circle in the middle of a white rectangle and you apply it as an opacity map, the surface appears to have a hole in it where the circle maps onto the object."

Trial and Error
And, of course, there's always the proper mapping of the textures to the objects . . . but that's another ballgame altogether! This should get you started down the road of material gurudom. The real road involves lots of trial and error, as materials and colors are tricky to understand just from reading an article. You need to spend some time and do some serious experimenting to get your arms around it. Until next month -- Happy AutoCADing!

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