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EiffelGeo: Eiffel Basic Geometry Cluster

Written by Javier Alonso.

• Targets Visual Eiffel 2.5 and ISE Eiffel.
• 29 September 1998.
• Eiffel Forum Freeware License.

EiffelGeo.zip (24,468 bytes) - source code

Introduction

This small cluster was created as a part of a CAD CAM system still under development. Its basic functionality is to provide access to the most basic geometry calculations, as needed in such a system to create and store descriptions of the tool paths necessary to manufacture parts in a CNC controlled machine-tool.

The cluster itself and any subsequent releases or derivates is understood to be distributed under the Eiffel Forum Freeware License (See included file forum_license.txt).

Structure

The cluster is composed by the following classes:

• cad_item: The generic ( and deferred ) anchor class. It introduces three attributes used when determining where the item is picked under some cursor position,

pick_point : INTEGER
pick_x, pick_y : DOUBLE

and two deferred queries:

id : INTEGER, to assure correct assignement with ?=
and is_under_rect(x1, y1, x2, y2 : DOUBLE ) : BOOLEAN to check if the item is picked and fulfill pick_point and pick coordinates.

• cad_item_constants, from which cad_item inherits, defines the identity constants for the heirs of cad_item and the pick_point places.

The effective descendants of cad_item implemented until now are:

• line, straight line in 3D space.
• circle, arc and ellipse flat figures with accessory Z component.
• catrom Catmull-Rom curve, also known as spline under tension and other names, useful due to the fact that it passes over all its control points.

And the rest of auxiliar files:

• parametric_comparisons introduces boolean comparisons of magnitudes within a tolerance factor.
• double_geo, heir of double_geo_constants provides some basic functions, trigonometry and the like, all with DOUBLE precission types.
• point_3d, basic supplier for cad_item heirs, inherits from the former two.
• ple_xy and ile_xy are the two equations for the line in 2D space, useful for intersection evaluation.
• np_dxf_file is a first attempt to read DXF files á la object oriented. Maybe should be subclustered in its own.It is still a somere draft used to read only LINE, ARC and CIRCLE entities.

Things to do, and evolution trends

At the moment of writing ( mid Sep. 1998 ), this cluster is still in its infancy. It has fulfilled my punctual needs in my systems under actual development and seems to work as intended. Anyway, the lack of a more complete geometry library for Eiffel ( and my future needs, too! ) makes me think as worthwhile the effort of extending and refining this very basic bunch of classes with the following subclusters ( some of them in some stage of planning and even alpha testing ):

• Vectors: normals, dot and cross products.
• Matrix algebra: 2/3D transformations.
• 2/3D NURBS.
• Curve based Surfaces.
• Solid Modeling. ( desirably with Constructive Solid Geometry ).
• Rendering ( OpenGL based, coming first ).

Aknowledgements

The data structure being almost totally mine ( or obvious ), the vast majority of the algorithms employed have been extracted from classic text books, the Wavefront file format specs and, most of them, from the classic Graphics Gems collection.

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