The Temporary Drawings

For each Detailed Compare Job up to six temporary drawings can be generated. These temporary drawings are regular DWG's.

CompareDWG first scans through the old file. Each entity in this drawing is written to exactly one temporary drawing:

  • If the old entity no longer exists in the New Drawing, it goes into "Old Drawing - deleted entities". This file is called FRXC_ODL.DWG.
  • If the old entity still exists in the New Drawing but something in its definition has changed, it goes into "Old Drawing - changed entities". This file is called FRXC_OCH.DWG.
  • If the old entity is present in the New Drawing with exactly the same definition, then it goes into "Old Drawing - unchanged entities". This file is called FRXC_OUN.DWG.

Next a similar scan through the New Drawing will create the temporary drawings "New Drawing - added entities" (FRXC_NAD.DWG), "New Drawing - changed entities" (FRXC_NCH.DWG) and "New Drawing - unchanged entities" (FRXC_NUN.DWG).

For changed entities it will be clear that two temporary drawings are needed, one that shows the changed entities as they were before the change and one that shows them as they are after the change.

For unchanged entities this may need some explanation: "If these entities are unchanged, why do I need two files that contain the same entities?". This is because the entities themselves are unchanged, but they may still look different if the symbol table definitions have been changed.
An example: if both input drawings contain a polyline that has been drawn using linetype BORDER, and nothing has been changed to the polyline, then the polyline will be reported as Unchanged. However, if the New Drawing contains a different definition of the linetype BORDER then the polylines may still look different. Similar effects may happen if any other definitions have been changed, including block definitions.
To spot these differences it is important that you inspect the reports for each compare job.
For clarity: if an entity uses a different linetype then the entity will always be reported as changed. It is only when the entity uses the same linetype but the linetype definition has changed that you must draw your conclusions from the reports.
This behaviour is as designed: it ensures that a minor change to, for example, a linetype or layer definition will not automatically declare large parts of the drawing as changed.

Some final remarks:

  • Views are copied to all three (old or new) temporary drawings. This is an exception to the rule that entities are copied into exactly one temporary drawing.
  • Vertices will always be included in the same temporary drawing as their parent.
  • Attributes will always be included in the same temporary drawing as their parent.
  • Dimensions will usually, but not necessarily, go into the same file as the object(-s) they are measuring.
  • Xrefs are not copied into any temporary drawing.