Open Objects.-
As has been shown in the corresponding page of
the Menu, in Metagraf there are available the open objects that
follows. All the open objects accept to be "decorated" with
arrows, except the point.
Point. This object is the simplest one. It is just, as his name implies, a point draw at a certain coordinates par that defines his position. Nevertheless, it has all the standard attributes of the more complicated objects: color, thickness, edit ability...etc. Without the Variational Geometry, the interest of this object is limited. It does not support arrows.
Line. It is understood for this object, that it is a "right line". For its definition it is needed to define two points with its coordinates. The Line is very simply edited as will be shown and can be transformed: rotated, scaled...etc., like any other.
Polyline. The equivalent to the Polygon but in open shape. It is needed to define a number of points equal to the number of sides plus one. All the standard attributes, including transformations, can be applied to it.
Bezier. This line is a curved one. Many computer applications includes this kind of curve, that have a direct translation to Metapost. In Metagraf, it is drawn as if it were a polyline, and the curve created is corrected when odds points are created. This is so to maintain a first order geometrically continuity. It should be used an even number of points.
Bspline. This is a more sophisticated way of drawing curves that are a "step higher" in quality over the beziers, in the sense of a bigger continuity -up to second degree- so, with continuity not only between the tangents, but also between the curvatures.
Nurb. In a simple way, it is possible to say that a Nurb -in Metagraf- is a Bezier curve with an added capability: the possibility of giving "weight" to the points defining the original Bezier, transforming it in a technically "rational" Bezier. This weights represent a kind of attraction, or repulsion, over the general shape of the curve from every point defining it. This allows to draw perfect conics using Nurbs, what is not possible with normal Beziers. The simplest way to understand Nurbs is trough practical drawing in Metagraf's drawing screen.
Spiral. Of no continuous use, it is very interesting to have it when needed. It can be drawn in a clockwise or counterclockwise way, and the shape can be defined at drawing time, but also modified afterwards. An arrow placed on its origin has no sense.
Angle. The object Angle, in fact an arc of an angle, is a very common and needed object in many drawing activities. Quite a lot more will be said about this object later on.
Madrid, January 2006 |
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