A cheap trick:
In a top down model, you can use the POINT OBJECT command to change the facing of your models. The mouse X is your x axis, your mouse Y is the z axis, and you set the the y axis to the same value as your pivoting model's Y position.
This is assuming that your 3D world has similar coordinates to the
screen. The trick comes in play when the scale is different or you need to apply an offset. This is not too difficult to do, but it varies from program to program.
The not so cheap trick:
In DBP, v5 or higher you can use the PICK OBJECT command to select floor tiles or other objects and return that object ID. With the object ID, you can get the tile's position and use that for your POINT OBJECT command.
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TAZ