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Comparing Entities

This chapter applies to Detailed Comparisons only, not to Basic Comparisons.

The method CompareDWG uses for comparing is a database driven method, not a graphics driven method. For each matching entity, the AutoCAD database definition in the Old Drawing is compared against the AutoCAD database definition in the New Drawing.

An entity that occurs in both drawings is regarded as the same entity if:

It has the same handle,
It is in the same space (Modelspace or Paperspace), and
And it is exactly the same entity type (e.g. a circle or a 2dPolyline).

For entities, CompareDWG compares all standard AutoCAD definition data (except for proprietary data used by 3dSolids, Bodies, Regions, Proxies, OleFrames and Ole2Frames).
Xdata will be compared if you have specified this in your Preferences.
Use the CompareDWG command Entity Definition to see what exactly is compared for a specific entity.

Some remarks about special entities and special data items:

Anonymous blocks

These are hidden blocks that AutoCAD creates to support dimensioning and (in earlier releases) hatches. They are compared where appropriate. However, AutoCAD reserves the right to change names of anonymous blocks (and actually does it), so these names are not compared.
Anonymous blocks are not included in the counts.

Custom entities

These are entity types that have been defined by third parties; they have been added to AutoCAD's standard repertoire of entities. Due to their nature, they could be anything; it is impossible to guarantee that they will be supported. However, if they are developed according to the AutoCAD standards, you will often find that CompareDWG can support them.
For best results, make sure that you have the program (ARX) loaded that supports the definition of the custom entity before calling CompareDWG. Otherwise AutoCAD will convert the entities into so-called proxy entities (also called zombies in earlier releases). CompareDWG can compare drawings with proxies, but it can only see the existence of the proxies, it cannot check their details. The proxies are copied to all temporary drawings. Also, CompareDWG cannot display drawings with proxies using markup colours. You must either load the appropriate ARX and compare again, or inspect the temporary files by opening them with the regular AutoCAD commands.

Dimensions

If the input drawings may have used dimension style overrides, it is important to have the Xdata switched on in your preferences, since this is where the overrides are stored.
As with all table references, a change to the table definition (the dimstyle) does not automatically mark all entities that use this dimstyle as changed.

Lines etc.

AutoCAD supports lines, 2dPoylines, 3dPolylines and lightweight polylines. All these linetypes may be present in the same drawing. CompareDWG supports all of them, they will be reported separately. Please be aware of conversion issues if you use old AutoCAD 13 drawings.

Hatches

Hatches will be compared and reported if changed. Most hatches will also be coloured according to your markup colours. However, gradient hatches will always be displayed with their original colours.

Mtext

In the font selection of an Mtext you can include special codes that overrule AutoCAD's colour definition for this Mtext. In this case your chosen markup colours will also be overridden by the hardcoded font colour.

OleFrame and Ole2Frame

These entities are not compared. Drawings with these entities cannot be displayed with Markup Colours, not in Detailed Mode nor in Basic Mode. You can however, generate the temporary drawings in Detailed Mode and open these in AutoCAD for manual inspection.

Proxies

See Custom Entities

Pointers

These are compared to see if they refer to an object with the same handle in both drawings.

Raster Images

The insert is compared. The actual raster is stored in an object, which is not compared. This means that CompareDWG will tell you if for example an image is missing, but it will not tell you that the contents of the image have changed.

Viewports

Viewport entities only exist in Paperspace, they will not be checked by CompareDWG. As with all Paperspace entities, viewports will always be written to all temporary drawings. In other words, the three temporary drawings that are based on the Old Drawing will always contain all viewports defined in the Old Drawing. This allows the user to view the temporary drawings properly using the viewports (open the temporary drawings manually).
However, no paperspace information is available in the result drawings, which are shown in AutoCAD.

Xdata

Data stored in Xdata is compared if you have specified this in your Preferences.

Xrecords

Data stored in Xrecords is not compared.

Xrefs

Xrefs are counted, but CompareDWG does not look "into" the attached Xrefs to see if they have changed. To make this clear in the reporting, Xrefs will always be counted as Added or Deleted, never as Changed or Unchanged. If you want to check if anything has changed in the Xrefs, then you must run a separate compare job on the Xrefs.
Furthermore Xrefs are not written to the temporary drawings.

Zombies