As a mathematician, you generally want to depict a specific portion of the Cartesian plane, and may want to control the aspect ratio of the figure, for reasons including aesthetics and mathematical accuracy. In the LATEX picture environment, locations are specified in terms of the current LATEX unitlength, measured from the lower left corner of the LATEX picture box. There are at least three unfortunate consequences of this design. First, the position of each object must be computed by hand in a coordinate system that usually has little to do with the figure. Second, while a figure can be scaled easily by changing the unitlength, it is impossible to change the aspect ratio of a figure without manually changing the positions of each object. Third, raw scaling can easily break a figure, because text does not scale. Thus even changing the size of a LATEX figure can be non-trivial. ePiX circumvents these problems; this is discussed at more length in Section 3.
In order to draw a figure in ePiX, you must provide the following pieces of information: the unitlength in the figure, the size of the printed figure in picture coordinates, and the Cartesian coordinates of the figure's bounding box. ePiX performs the following affine scaling automatically:
Changing the size, aspect ratio, or bounding box of a figure is therefore trivial, and if the figure is well-designed it will scale attractively. Objects may extend outside the bounding box, but you generally have better control over figures that exactly fill their bounding box. The entire figure may be offset, as in the LATEX picture environment; if unspecified the offset is zero. In contrast to LATEX , positive offsets in ePiX shift the figure up and right.