Circles and Spirals.-
There are two ways of drawing circles in Mg5. The most direct is to use the object “Circle”. This object has some peculiarities, the principal one is that it does not allow the user to change its circular shape. It can be scaled in both directions or made bigger or smaller by simply selecting the extreme of its radius, shown as a small point in selected state, and moving it with the mouse or with the arrow-keys. The same is allowed with its center. But if the user tries to scale it in only one direction, it will refuse to do so and nothing will happen.
Sometimes, there are drawings where circular things should remain circular although the whole drawing will be scaled. A car, for example, can be longer or shorter, but it can't have elliptical “Firestone”. This is the reason to have provided the circle object.
The other way of creating a circle is by drawing an ellipse with equal length of its vertical and horizontal axis. Mg5 provides a simple way to draw this kind of circle without losing much time looking for the precision of this operation. When creating objects defined by points and the union trough lines of this points are different from the object, the polygon formed by the lines joining the defining points will appear only in selected state and will be draw as a thin blue contour line.
This “blue polygon” is part of the object so it can be used to select the whole object, for example when a point is selected and it is wanted to change to the selection of the whole object, those lines can be clicked for doing so. If it is wanted to create a circle as a special ellipse, that will allow any kind of affine transformation, the blue polygon of the object ellipse, will change to a red square when width and height are equal in length. Moving the mouse or the arrow-keys when one point is selected, it is simple to find the “circular situation” when the external polygon changes its color from blue to red.
An immediate application of this facility is its use when creating spirals. Those objects use external ellipses as their forming polygons. If can be wanted to have an elliptical spiral, although, usually, it is more common the circular one. (The spiral object can also use the “Data window” for special cases).
Madrid, January 2006 |
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