PNG → CAD Block — LAAR 61400

PNG

PNG → CAD Block

Turning a raster tree into a scaled, reusable AutoCAD block

LAAR 61400

A PNG tree is pixels. A CAD block is geometry with a name, a base point and a real size, inserted once and repeated at 1:1 across the drawing. Tracing is only the conversion — scaling and blocking are what make it usable. Three routes below end in the same place: a .dwg in your block library. Start with the first one, because the cheapest block is the one you do not draw.

Route A — Download and reuse

Somebody already drew it. Two libraries to download sit below. Fastest by far, until the one you need is missing.

Route B — Illustrator Image Trace

Visual, one tree at a time, full control over how much detail survives. Use it for a symbol you will look at closely.

Route C — Claude Code

Yes, this works in code, and you never touch a terminal. Best when twenty silhouettes need identical treatment.

Route A — Download and reuse

The fastest block is the one somebody already drew. Entourage libraries circulate freely, and a competent drafter starts by looking for one rather than tracing. Two to start with, trees for AutoCAD and people and cars for Rhino:

↓ tr-08.dwg — trees, AutoCAD 2004 format, 2.2 MB ↓ entourage.3dm — people and cars, Rhino, 3.1 MB

A Rhino file is not a dead end for AutoCAD. Open the 3dm, select what you want, and Export Selected as .dwg — or Save As the whole file. Pick the 2007 Natural scheme for 2D linework. It travels the other way too, which is why Rhino is the useful middleman whenever a file refuses to open where you need it.

Open the donor file first

Open it on its own and look before you borrow. Run DIST across something you can size by eye — a person is about 1.75 m, a car about 4.5 m long. That one measurement tells you the file's units, which is the thing that goes wrong most often.

Bring the block across

AutoCAD. Copy the block you want, then PASTEBLOCK into your drawing. Or use DESIGNCENTER to pull single blocks out of the donor file without opening it.
Rhino. Insert for a block instance, Import to bring the geometry in loose.
Re-measure after it lands. If it came in at the wrong size, SCALE with the Reference option against a dimension you know.

Clean up what you inherited

Borrowed files carry layers, text styles and dimension styles you never asked for. Run PURGE and then AUDIT after inserting. If the block will become part of your own library, redefine it on layer 0 with colour ByBlock and a base point you choose.

For anything beyond these two, three places are worth a look before the general block sites: manufacturers publish blocks for their own benches, bollards and light fittings; city open-data portals carry street trees and curb geometry; and your studio's past projects already hold blocks someone on your floor drew and can vouch for.

Know where a block came from. Plenty of what circulates online was scraped from somewhere else, and a heavy downloaded block can carry thousands of vertices into a drawing it will never leave. Check the weight, check the licence before anything goes into public work, and credit the source when a drawing leans on someone else's library.

When Route A runs out: the species is wrong, the style clashes with your drawing, or the plan symbol you need does not exist in anyone's library. That is when you make your own — which is the rest of this page.

Before you trace — prepare the PNG

Get a clean silhouette

Tracing reads contrast, so the quality of the trace is decided before Illustrator opens.

High contrast. A dark tree on a white or transparent background. A photograph of a tree traces into mud.
Big enough. 1000 px or more across the canopy. Tracing a 200 px thumbnail bakes the pixel staircase into your curves.
Cropped. Anything else left in frame becomes geometry.
Real size known. Decide the canopy diameter now — say 6 m for a street tree, 12 m for a mature oak. You need that number twice below.

Route B — Illustrator → AutoCAD

Place the image

File → Place, with Link unchecked so the pixels travel inside the file.

Image Trace

Select the image, open Window → Image Trace, start from the Black and White Logo preset, then open Advanced:

Setting	What it does
Threshold	The cutoff between black and white. Raise it to capture more canopy, lower it to drop grey noise. The single most important slider.
Paths	How tightly curves hug the pixels. Lower gives smoother, lighter geometry; high values produce thousands of vertices that make AutoCAD crawl.
Corners	How readily a curve becomes a sharp corner. Keep it low for foliage, high for hard-edged symbols.
Noise	Ignores blobs below this pixel count. Raise it to kill speckle.
Ignore White	Check it, or a white rectangle rides along behind the tree and arrives in CAD as a solid.

Watch the path count at the bottom of the panel. A few hundred paths is healthy for a plan symbol.

Expand and simplify

Object → Expand turns the live trace into real paths. Then Object → Path → Simplify, pulling the slider down until the shape is about to change — that point is your vertex budget.

Delete leftover white shapes and stray specks. Set fill to none and stroke to black so you can see the outlines you are actually exporting.

Export DXF

File → Export → Export As, format AutoCAD Interchange File (.dxf). In the options: version 2007 or later, 1 unit = 1 mm, Preserve appearance off, Outline text on.

If the DXF arrives broken — curves exploded into hundreds of tiny arcs, or nothing visible at all — export an .eps instead, open it in Rhino and Export Selected as DXF. Rhino's DXF writer is far more reliable than Illustrator's, and it gives you curve-degree control on the way through.

Scale to real size

Open the DXF in AutoCAD, select everything, run SCALE and take the Reference option: pick the two edges of the canopy, then type the real canopy width. The tree now measures what a tree measures. Confirm with DIST before going on.

Make the block

Move the geometry to layer 0 and set colour, linetype and lineweight to ByBlock. That is what lets the block take on the look of whatever layer you insert it on.
Run WBLOCK, base point at the trunk centre — the point you will snap to survey coordinates.
Name it for what it is and how big it is: TREE-DECID-06M.dwg, saved in a blocks folder beside the project.

WBLOCK rather than BLOCK: BLOCK lives inside one drawing. WBLOCK writes a standalone .dwg you can insert into any drawing, in any project, for the rest of the semester.

Route C — Claude Code, no Illustrator

Tracing is contour-finding, and contour-finding is a solved problem. You do not need Python, pip or a command prompt for this — Claude Code installs what it needs, writes the script and runs it for you. You supply the tree, the real size and the judgement. Set Claude Code up the way WF07 describes, then:

Make a folder

Put your silhouette PNGs in it, plus the spec file below. Open Claude Code in that folder.

↓ Download the build spec — png2dxf-spec.md

Ask in one line

Read png2dxf-spec.md and turn tree.png into a CAD block 6 m wide.

The spec carries the detail — libraries, contour mode, base point at the trunk, geometry on layer 0 — so your prompt stays short. That division is the lesson: write the standing requirements down once, ask in a sentence.

Keep talking

The first result is a draft. Say what is wrong in plain language:

The outline is too jagged — simplify it more. The canopy holes came in filled. Do every PNG in this folder, all 12 m wide.

Open the DXF in AutoCAD and the block is already defined, already the right size, already built on layer 0. Run WBLOCK once to write it into your library.

Check the result, not the code. Measure the canopy, look for open holes, and grab the block by its base point. If any of the three is wrong, say so and ask for a fix. Accepting output you have not checked is the one habit that makes this route worse than tracing by hand.

Where downloading wins: the common stuff — people, cars, a generic street tree. Where code wins: twenty silhouettes traced with identical settings and identical canopy widths, from one sentence. Where Illustrator wins: the one tree you will look at closely, where the threshold slider is a design decision. Choose by the shape of the job rather than by the tool you already know.

Things that go wrong

Symptom	Cause and fix
Tree arrives the size of a city block	DXF units never matched drawing units. Use SCALE → Reference against the known canopy width rather than guessing a factor.
Solid rectangle behind the tree	Ignore White was off during the trace. Delete the shape in Illustrator and export again.
Drawing crawls after inserting	Too many vertices. Re-trace with lower Paths, or ask for a simpler outline. A plan tree rarely needs more than a few hundred points.
Block ignores its layer colour	The geometry carries an explicit colour. Redefine it with everything on layer 0 and colour ByBlock.
Trees refuse to land on the survey point	Base point sits at a canopy corner. Redefine the block with the base at the trunk centre.
Canopy holes come in filled	The trace kept outer contours only. In Illustrator select all paths and use Object → Compound Path → Make.

Worked examples

Two traces, source beside result.

One photographic tree

Photographic elevation of a tree on a transparent background — Source: a cut-out photograph, transparent background.

The same tree traced at three settings, showing 55, 2 and 1 closed loops — Same file, three settings. Raw: 55 loops, 1695 vertices. Close 9 px: 2 loops, 271. Close 15 px: one outline, 148.

Four trees in one image

Stock illustration strip of four multi-stem amelanchier trees on white — Source: four amelanchier on white, about 220 px tall each.

The four amelanchier traced into separate CAD blocks, five metres tall — Four separate blocks, each 5 m tall with its base point at the trunk, 500 to 630 vertices apiece.

One image, four blocks: split the trees apart first, and keep the close light so the multiple stems stay open.

Trace images you hold the rights to — these two are classroom examples.