IGES - How data loss can occur

Neutral format data exchange standards such as IGES and STEP are extensive in structure and scope. This is in an attempt to support a varied field of disciplines; MCAD and AEC are only two among many. In the process of neutral format data exchange, a 3D model file is translated from one native CAD format (sending system) to an IGES or STEP file. This file is then translated into another native CAD format (receiving system).

The process involves extensive entity mapping. The sending system maps native entities to supported neutral entities. The receiving system then has to map the neutral entities in the IGES or STEP file into its own native CAD entities. Sometimes this entity mapping can change the definition of the native CAD entity, such as mapping an analytical arc or cylinder to a b-spline curve surface. During the process, the original definition of an entity can get lost. This loss of definition in most cases has become acceptable.

Also, because of the size and scope of the standard, MCAD systems will only support a subset of the standard. While System A may support entities a,b,c,d and e, System B only supports entities a, c and e. So you ask, what happens to entities b and d? Well, they are ignored by System B because it chooses not to support those entities. This is another way in which data can be lost (see figure above).

This is not to say that data is lost due to nonsupport during every translation. This can occur when the two systems are fundamentally incompatible (such as between a high-end and a low-end system) or when the receiving system is outdated.

3D data loss can also occur due to human programming errors - how well the MCAD systems write out (translate to IGES or STEP) and read in data (translate from IGES and STEP). How well you say? Well that depends on how true the programmers that write the translators are to the specifications documented in standards.

The specifications are open to interpretation and programmers then have to program their translators to act accordingly. Programmers are also human and are prone to human error.

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