Interoperable interactive geometry for Europe
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Direction is an auxiliary symbol which is used to provide a direction in a ray element. It is the same as a vector but used in the elements part of the construction, where no references to vectors can appear.

If a direction has two components, they are to be understood as euclidean coordinates; and if it has three, they are homogeneous coordinates. (Note for the future: if the previous point in the element was a 3D point, then a direction with 3 components would be understood as euclidean coordinates, and directions with 4 components would be interpreted as homogeneous coordinates).

For instance, the ray that starts at (1,1) and moves to the right could be described by using any of these two elements:

<ray id="r">

<ray id="r"> <euclidean_coordinates> <double>1</double> <double>1</double> </homogeneous_coordinates> <direction> <double>1</double> <double>0</double> <double>1</double> </direction> </ray>


Some example should be provided