Chapter 4 Starting with GDL
3D View Click the ‘3D View’ button (of the library part, not the project) and you will see this. These objects all exist in the same space and overlap each other, so we need to find a way to separate them. The wireframe view shows each of the objects and the shaded view shows you how well GDL permits objects to ‘collide’ like this in the shaded view without harm.
Check Script If, when you click the 3D window, it refuses to draw because of an error, return to your script and click the ‘Check Script’ button. This will point to the line where the error occurred, usually because of a wrongly placed comma, or a spelling error. Do this often when writing GDL.
3D Space and the 3D Cursor You need to move about in 3D space to be able to place elements such as the legs of a chair, or a tabletop. Movement around the model is done with ADD commands. These work on the logical idea that the 3D world can be thought of in three cardinal rectilinear directions called X, Y and Z. You should be familiar with the idea of X, Y and Z from the normal ArchiCAD environment – the Coordinates palette allows you to enter a dimension in X or Y (and you can also enter radial dimensions and angles). In GDL, we use X and Y; Z is used to provide vertical movement.
The three-pointed object that you can see in a GDL 3D view reminds you which ways are X, Y, or Z. This is like a 3D Cursor. When you word process, you are used to the idea of a cursor – wherever you place the cursor, you can begin typing, and whatever you type appears. In GDL, there are two of these, one at the origin, and one where you have moved to. The one labelled ‘G’ is the Global Origin of the GDL model. The one labelled ‘L’ is the Local Origin, referred to here as ‘3D cursor’, for short. Wherever this is, your next 3D command will happen. Using the ADD command, you can move the 3D cursor about in 3D space in a single XYZ move. ADDX, ADDY, or ADDZ move the 3D cursor in those axial directions, in one direction only. The importance of DEL It is a good discipline to return the cursor back to the origin as often as possible. GDL remembers every cursor move you have made. The DEL command undoes or ‘deletes’ these movements, allowing the cursor to retreat back to the origin, leaving the 3D elements behind. 2D Cursor movement When you are writing GDL in 2D, you have a similar concept of X and Y based 2D space. You do not have to worry about height. Using the ADD2, ROT2 and DEL commands, you can move about in 2D space providing you specify both the X and Y distances. Unfortunately, you do not have a visible cursor. You can Rotate, Shrink and Stretch In reality, the 3D world is too complex to be defined ONLY in absolute terms of X, Y and Z. So you will be glad to know that you are also able to Rotate the 3D cursor (using the ROT command) and move radially, and work at different angles from the pure horizontal and vertical. You are also able to shrink or expand the cursor (using the MUL command which multiplies) so you can easily deform or mirror elements of your model.
Introduction to Object Making with ArchiCAD
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