by Dennis Collin
I was having a conversation with a customer who was having a problem locating geometry correctly within an XREF drawing. When referencing this DWG file into another container drawing at 0,0,0, the geometry in the XREF was shown offset from its true position.
Fig 1. When referencing other consultant’s drawings, do not scale and insert at 0,0,0.
When working with External reference files (XREFs) it is vital that the current UCS used is AutoCAD's global coordinate system (WCS). This can be verified by ensuring the UCSICON (if displayed) shows a box or W. Alternatively check the View cube interface and confirm the current UCS shows as World.
Fig 2. Both the View cube and the UCS Icon indicate the WCS is the current coordinate system.
However, XREFs can still locate incorrectly if attached if the system variable INSBASE has been changed. The AutoCAD system variable INSBASE contains the insertion base point of a drawing. The base point is expressed as coordinates in the current UCS. When inserting or externally referencing the current drawing into other drawings, this base point is used as the insertion base point. This may be used to enable the use of relatively small local coordinates within a drawing, but still have the drawing insert or reference in the correct location relative to a much larger coordinate system. However, this situation is rare, and my general advice is to leave the INSBASE variable at the default value.
Fig 3. The default value should be 0,0,0 unless there is a good reason otherwise!
If the INSBASE value changes, the culprit could be an external LISP/ARX routine so if any anomalies become apparent, I would check that the WCS is set as current and the INSBASE variable reads 0,0,0
Fig 4. When Referencing drawings the current coordinates system should be set to World (WCS)
With this example, the value of INSBASE had been changed from 0,0,0. But by using the BASE command, the insertion base point was rest back to 0,0,0. Once set, the dwg referenced into the container drawing at 0,0,0, and the geometry in the XREF was shown at its true position as expected.
Fig 5. Several linked Xrefs all in the correct place. Ready for export!
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