What is a ʼPDF Underlayʼ in BricsCAD?
Short Answer
A pdf underlay in BricsCAD is a referenced PDF file you attach to a drawing for tracing, coordination, or background drafting using PDFATTACH. It behaves like an external reference, so you can move, scale, clip, and fade it without converting it to CAD geometry. Limitation: PDF underlays are not natively editable as drawing objects.
What You Need to Know Before
Warning: PDF underlays often look accurate but may contain scanned or distorted content, so snapping and measuring from them can be unreliable. If the PDF was created at the wrong scale or includes raster pages, your traced geometry can be permanently off.
How to Attach a PDF Underlay in BricsCAD
Command: PDFATTACH
Shortcut: No default shortcut in most standard workspaces
Quick Steps:
- Go to the Insert tab on the Ribbon and choose Attach PDF, or type
PDFATTACH. - Select the PDF file, then choose the page to attach and set Path type if prompted.
- Specify the insertion point, scale, and rotation, or enable on-screen placement options before placing it in the drawing.
- Go to the Insert tab on the Ribbon and choose Attach PDF, or type
Variables & Settings
Key Setting: Contrast / Fade / Monochrome in the PDF underlay properties
Expert Setting: These properties control underlay visibility and usability during tracing. Increasing Fade makes linework easier to draft over, while Monochrome can improve readability when the source PDF has poor color contrast.
Why it Fails
- Cause 1 (Geometry): The attached PDF is raster-based or scanned, so linework is only an image and cannot provide reliable vector snapping.
- Cause 2 (layers/Locks): The underlay is on a locked, frozen, or non-printing layer, so users think it is missing or uneditable.
- Cause 3 (Command/Logic): The PDF was inserted with the wrong scale or rotation, so traced geometry does not match actual model dimensions.
Quick Fix & Best Practice
- Quick Fix: Select the underlay and correct its scale in the Properties panel, then use clipping if needed to isolate the usable area.
- Manager’s Verdict: Use PDF underlays for background reference, markups, and tracing when native DWG files are unavailable. Avoid using them as a dimensional authority unless you have verified scale against a known distance.
FAQ
Can you snap to a PDF Underlay in BricsCAD?
Only reliably if the PDF contains vector data, not just a scanned image.
Can a PDF Underlay be clipped in BricsCAD?
Yes, you can clip it to show only the needed area.
Is a PDF Underlay the same as imported PDF geometry?
No, an underlay is a reference attachment, while imported PDF content becomes drawing geometry when supported.
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