UVW Mapping Basics

• For this discussion, we will NOT be using "Real World Map Scale".  To turn this off by default, go to Customize - Preferences, and in the General tab, un-check the box that is labeled, "Use Real-World Texture Coordinates".  Although it sounds counter-intuitive, Real World Map Scale is actually more difficult to use when you understand how UVW mapping works. 

UVW mapping deals with the scale and positioning of a material onto an object.  It is a "projector" helper object, in that it takes a 2D image and projects it into 3D space onto geometry. 

If the material is set to Tile, which it does by default, the material will repeat in each direction beyond the UVW map's size.  If the UVW map is set to tile, it will divide the UVW map into equal parts and tile the texture within the UVW map's size. 

Without UVW coordinates, there is no way to scale the material on the object, much less accurately portray a material. 

The following image has UVW mapping coordinates only via the automatic generation of mapping coordinates at an object's creation.  Each object receives the exact same material:  Brick.  The problem is that on each surface, the brick is a different size.  The brick should not change size from one surface to another - it's a standard size modular unit. 

Let's place a UVW modifier on both objects. 

• In the Modify Panel, drop down the list of modifiers and select UVW Map. 

• Place a UVW map on each object. 

• In the parameters, we have several options on the Mapping "Shape", "Size", and "Tiling".  Let's start by selecting a shape that's closest to the shape of our object - the box. 

• We are going to size the UVW map -- this will change the size of each brick.  Think of the plane of the UVW map's gizmo being the image you are mapping onto the object.  As you make the box smaller, the image is getting smaller.  if you "squash" the box, you are "squashing" the image to be mapped. 

Let's examine the actual brick texture that is in the Diffuse map slot. 
 

• If you know the size of an individual brick, and you know how many bricks are in the height direction of the image, you can be very accurate in how large the bricks should be.  Let's use 2-1/2" as the height of a brick in this case.  We have 24 bricks, so the total height for this tile should be 60".  Therefore the size of our UVW map should be 60" x 60" x 60", since the image is also a square. 

• This size will not change for any instances of this particular brick.  So the modify panel for the UVW map will look the same for every object that has that particular material on it. 

• Now, the brick is the same size on each object, and it also has a realistic scale for a convincing scene. 

• Often, you will not need to be this accurate, even if you are able.  In most cases it is an approximation. 

• In addition to sizing the brick, we can also use the UVW gizmo to position the bricks on the surfaces.  In the Sub-Object mode of the UVW Map, you will see Gizmo.  Using the Move tool and the Transform Gizmo (the XYZ indicator on the screen), you can position the bricks on the surface. 

Cylinders and Spheres have a slightly different method, because regardless of the distance away from the surface, as long as the UVW map has the same shape as the object it is assigned to, the map will be projected perpendicular to the object surface. 

• In the following image, a cylinder is mapped with a UVW Map, and the U and V scale on the left image set to 4'-0". The U and V scale on the right are set to 8'-0".  Although the scale of the U and V directions doubled, the brick texture on the surface remained the same size. 

• By changing the U tiling, however, the brick image in the diffuse color slot is divided within the cylindrical "wrapper".  This will scale the brick around the cylinder's surface. 

• A similar methodology is also used on spherical maps.  Rather than changing the UVW size, change the UVW tiling to produce scaling results. 

Often, in the case of a Multi/Sub object material especially, more than one material scale will be required on a single object.  Let's consider the following wall:

In this case, the stucco on the inside should scale differently than the brick on the outside.  Because it is a single object, however, placing a single UVW Map modifier on the object will scale both the brick and the stucco at the same rate.  In order to scale them differently, we will need to apply multiple UVW Map modifiers on the object and specify channels for each one that correspond to the material itself. 

•  To begin, because there are two distinct materials on the object, let's place two UVW Map modifiers on the object. 

•  Each UVW Map will be set to Box, but one of them will be set to Map Channel 1 and the other will be set to Map Channel 2. 

•  Before we can scale the two materials separately, however, we still need to match the material to the UVW Map Channel settings.  This is done directly to each bitmap in the material composition. 

• This is best done by using the Material / Map Navigator to quickly navigate from material to material and bitmap to bitmap. 

•  Within the navigator, each bitmap has a Mapping Coordinate setting.  The exact setting we are looking for is "Map Channel _____". 

• The bitmaps for the "Bricks" material will be assigned one of the mapping channels, and the bitmaps for the "stucco" material will be assigned the other.  The numerical values are irrelevant as long as you match them properly to the UVW Map Modifiers. 

• In this case, let's assign the bitmaps for the brick texture to 1 and the stucco texture to 2. 

• We can now scale the stucco by using the UVW Map Modifier that is assigned Map Channel 2, and the Brick by using the UVW Map Modifier assigned to Map Channel 1.  In the preceding image, the brick on the left is the same size as the brick on the right, but the stucco changes scale.