If I specify a material as using a bump map in the Define Material dialog, it allows me to set either a positive or negative value. What is the difference?
A bump map is an image file that makes a material appear non-flat in ray trace views, and though the effect of bump-maps are sometimes subtle, they add to a ray trace image’s quality; wood grain that shades appropriately to the lighting in the room, for example, lends to an appearance of realism.
To apply a bump map
Select a material in your library's User Catalog that you want to assign a bump map to, right click on it, and select Open from the contextual menu.
Alternately, you can use the 3D> Materials>Adjust Material Definition tool in a 3D camera view to select an object that has the material that you want to adjust.
Changing a material definition with this tool affects all objects in the current plan that are using that material.
It does not affect any materials saved in the library, or materials used in other plans.
On the Properties panel of the Define Material dialog, check the box beside Use Bump Map.
In version X2 and prior, this setting was located on the Raytrace tab.
Click the Browse button to browse to a bump map image file saved on your computer, or you can also type or paste the full path name of an image in the text field.
To use a bump map saved in a .zip file:
Type or copy the full path name of the .zip file in the text field.
(If you are using a Chief Architect material, you can locate the path name on the Texture panel for the purposes of copying and pasting it on to this panel.)
Directly after the path name, type #zip:, followed immediately by the name of the bump map file including its file extension.
The Height Multiplier allows you to specify how drastic the effect of the bump map is. The default value is 1” (10 mm), but larger values may give better results, depending on the bump map used.
In version X2 and prior, this setting was called Bump Height.
The difference between positive and negative values
Any image file or texture can be used as a bump map, with dark areas of the image corresponding to low points in the bump map, and brighter areas corresponding to high points.
Using the image below as a bump map:
A positive Height Multiplier value created the ray trace example view below.
Notice the raised effect that the light lettering has on this grey object, whereas the dark letting displays as more sunken in.
A negative Height Multiplier value reverses this effect:
Notice that now, the dark areas of the image correspond to high points, and brighter areas corresponding to low points.