 |
 |
 |
 |
|
||||
|
||||
| Updated 26/7/2003 |
Here is a simple technique for quickly aiming lights in order to get shadows to fall exactly where you want them.
All you need to do is create a pair of locators, then put one at a point on your shadow casting object and the other at the position on the ground (or some other object) where you want the shadow of that point to fall. Then use a constraint to make one locator point at the other, then another constraint to align the light to the locator.
To start with, create a simple box, a ground plane and a distant light, arranged something like this:
Create two locator nodes, and place the first one on a prominent point of your shadow casting object, e.g. the corner of a building, or the top of a character's head. We'll call this the Casting Locator.
The second locator is then positioned at the place where you wish that point to cast a shadow. In the example scene you can see we have placed one locator on the corner of the box, and the other at a point nearby on the ground. We'll call this second locator the Shadow Target Locator.
We now create an aim constraint so that the Casting Locator is always pointing at the Shadow Target Locator. Do this by selecting the target, then shift-click to select the Casting Locator, and select Animation->Constrain->Aim from Maya's menu, selecting the options box.
In the options box, change the Aim Vector from its default of <<1,0,0>> to be <<0,0,-1>> (i.e. we want to constrain negative z to point to the other locator). If you don't do this here then you can easily modify the constraint vector by selecting the constraint node in the Outliner, opening the Attribute Editor and changing it there.
You should now see that the locator is aimed properly, and dragging the other one around will cause this one to update to always point in the correct direction.
The final step is to select the Casting Locator, then shift-click your light, and create an orientation constrain from the Animation->Constrain->Orient menu.
This locks your light to always point in the same direction as the Casting Locator.
You now have your scene setup so that moving the two aiming locators will re-align your light to always cast shadows precisely where you want them to end up.
In the images below you can see the 3D view where I have created some text that I wish to aim my shadow at, and then the final render showing that it does indeed fall exactly on this position.
If you are integrating your 3D with live action background plates, then you can set the background images as the camera's image plane, and line up your two shadow aiming locators to match two points from the real image. That way you can be absolutely sure that your 3D shadows and lighting direction will match. This is of course dependent on having a correct camera track to start with.
If you have any questions about this tutorial you can email me here.