Let us see how TAD is different from other CAD software.

Unlike CAD, TAD uses a different paradigm to go about modeling. In TAD, you are not forced to think of a shape first and then go about creating that shape. Instead, TAD will give you a starting shape such as a rectangle, square, or a triangle. Or you can get TAD to base it on a previously existing shape in the model. 

You then quickly move into other aspects of the design holistically.

On the other hand, drafting software is often interrupting your design thinking. Once you think of a shape;  you would then need to break up that shape in your mind. Then think of the graphic commands for that shape. Should I use a poly line here?  What if I use a rectangle command? and so on.

Notice how you get pulled away from the logic of the design; into the way the drafting software works. Your thinking becomes strongly visual -- other aspects of the design recedes into the background.

That is the reason there can be a lot of difference between a drafting software expert and an amateur. It takes time to get away from the internal chatter of the commands of the software; and start concentrating on the actual designing.

On the other hand; TAD allows you to quickly build up the logic of your design. What is the name of the shape you are now inserting? Which class should it go into? What other logical elements would you need in your design? These are all questions directly related to your design. They need not be shape related.

Quite often you can even start taking decisions such as -- what is the distance between here and that element? Is the area of this shape roughly right? Is this shape roughly in the correct location? and so on.

Of course; the final shapes may be different from what TAD gave initially. You can use the editing commands in TAD to lovingly edit the previously created default shape; till the shape is exactly what you had in mind. You can even precisely locate the elements at the exact positions with respect to each other. 

The best part is that TAD does not dictate how you go about assembling your design elements. You can start your design in many different ways. This kind of software is called a "loosely coupled" system -- It does not have any rigidity or order that it would strictly enforce.

That is why TAD is such a joy to use in very early stages of your designing. Those are the times when you;; frankly, may not even know what are the geometric details of the shapes you want to use. All that can come whenever you are ready.

And if you really wanted to work on the shape right from the beginning; TAD will say "Be my guest", and you can do that exactly like a regular CAD software.

In short; TAD respects a logical way of looking at the design process. TAD allows you to move your design from the rough to the accurate. At your own pace. It does not force your hand to continually keep thinking of graphic shape commands. 

Later on, we will see that this loosely coupled way of working of TAD allows very flexible design iterations.

Conceptual Differences: TAD and CAD

Snapping in TAD and CAD. 

All CAD software have many snap commands. Such as snapping to vertices (that is; corners). intersection points, nearest points, mid-points and so on.

Before understanding the concept of "snaps", we need to understand essentially why they are needed. Both in TAD as well as CAD.

In CAD software; the mouse cursor plays a crucial role in guiding the graphic shape creation and  editing actions. 

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However, the CAD software is ever ready to handle the graphical entities that were drawn by the draftsman. That human is free to pick any graphical entity with his mouse. The CAD software does a good job to freely allow the draftsman whatever editing or creation action that he may invoke.  

In order to ensure that the editing happens accurately; the CAD software gives the draftsmen the capability to "snap" the mouse to the correct points just as the editing is going on.

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TAD does not work like CAD. Firstly; the mouse cursor is simply a "mouse cursor" most of the time. It is used to click on the user-interface elements such as menu items, buttons, etc. 
It can be used to select the objects in the TAD model. It can also drag or rotate objects. But except for those, the mouse cursor does NOT participate in either creation nor editing of the model.

For helping you with creation and editing; there are three special "persons" on the site. Yes, you can actually think of three human beings present right inside the model. Think of this like a computer game; where there are three persons simulated on the screen. 

These three persons are shown using 3 shapes. The first person is called the "architect". It looks like a tilted capital letter "A" placed inside a square. The other two persons are called "helpers" The first helper is shown as a red square dot. The second helper is a blue circular dot.

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...the location of the simulated architect is the point of interest for TAD. And therefore; the snap commands would shift that architect precisely.

Snapping in CAD software happens in the middle of the editing. But in TAD; the architect is snapped into the correct location BEFORE any editing/creating happens.  Those starting with TAD should get accustomed to this difference from CAD.

Remember; the simulated architect inside TAD is always located at some visible location. 

By the way; this architect can never be moved out of visibility. If you happen to zoom to another part of the site; where the simulated architect was absent; you would find that magically TAD would shift the architect into visibility: It would get transported to the centre of the new view of the model; even though the architect was not located there in the earlier view.

Why should snap work on this architect? The reason is; that architect is pointing out the exact point where creation and/or editing happens next in TAD.

TAD allows five types of snaps on this simulated architect. It can snap the architect onto the location of the first helper. Or the architect can be snapped to the second helper. Or the architect can be snapped to the foot of the perpendicular of that infinite line which contains the edge that has the two helpers. 

TAD also allows the architect to snap on a point of intersection between two edges. If that be the case; then one of the edges should be the one with the current helper.-- and also; the architect should be roughly located visually on the intersection.

Lastly; TAD allows the architect to snap on to any corner in the model. Again, for this snap to happen; the architect should be roughly located visually on the corner you expect to snap to.

What does "roughly located architect" mean? Remember that the icon used for this simulated architect is drawn inside a square. For the last 2 snaps; you need to drag and drop that architect so that the expected point is somewhere within the square of the architect's icon.

TAD Master