Turn repeated drawing fragments into AutoCAD blocks with AI

A floor plan can contain the same door symbol repeatedly, each copy still made from separate drawing objects. AutoCAD’s BDETECT command uses Autodesk AI to find and group similar geometry, ready for conversion into blocks. The task is to turn a visually repeated symbol into something the drawing can treat as one reusable object.[2]

This documentation-based walkthrough uses AutoCAD 2027 for Windows. BDETECT is available in full AutoCAD; the command table does not list it for AutoCAD LT. No drawing was processed for this article.[3]

Start with a plan you can inspect

Open the DWG and run SAVEAS to make a working copy under a different name. The new file becomes the current drawing. Choose one familiar family of symbols for this first pass, so you can recognise both missing parts and unwanted additions.[9]

Use a plan-view drawing with real-world units. Autodesk says detection is best suited to architectural objects such as doors and bathroom fixtures. Before starting, identify one complete example and inspect what belongs to it: a door leaf and swing arc, for instance, rather than an adjacent wall line.[1]

Choose the geometry that defines the family

Enter BDETECT. When analysis finishes, select a set in the Detect palette to highlight its instances. The review toolbar shows the count and lets you move between matches. Inspect examples around the drawing, including ones beside dense linework.[4]

The blue-bordered primary instance has a special job: its geometry becomes the definition of a new block. If you convert to an existing block instead, that instance establishes the insertion scale and rotation. Choosing the primary therefore affects more than which example is easiest to see.[1]

Use Change primary on the review toolbar to choose a better example. Edit primary lets you add or remove objects from that example; it is also available from the palette. For the door exercise, use this to leave the intended symbol together while excluding nearby drawing elements.[4]

Remove an unsuitable match from the set with DETECTREMOVE. An apparently similar symbol may represent a different item in your drawing. Excluding it keeps that distinction intact while you convert the genuinely matching instances.[5]

Make the block useful for the next edit

Choose conversion to a new block. In the Convert dialog, give it a clear name and specify the insertion point. The default point is the centre of the selected geometry; choose a position that makes sense for subsequent placement. For a door symbol, consider the hinge location as your working reference.[6]

After confirming the conversion, leave detection review with DETECTCLOSE. If an ordinary editing command appears unavailable during review, finish that mode first. Autodesk temporarily blocks commands including BEDIT and COUNT while it is active.[7][4]

Select a converted symbol and inspect its complete outline. A block reference should behave as one object. In View > Palettes > Blocks, find the new definition under the current drawing and try placing another copy in an empty part of your working file. Check the insertion point, orientation and scale, then remove the temporary copy.[8]

Save the working DWG and reopen it. Inspect one converted symbol beside its surrounding walls. The enduring change is the shared definition: editing that definition updates its references in the drawing. A few minutes spent deciding exactly what belongs in the first example can therefore shape many later edits.[8]

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