Lesson 5.07 – Creating Geometry with AutoLISP

🧱 Lesson 5.7 – Creating Geometry with AutoLISP

Automate the creation of LINE, CIRCLE, and RECTANGLE objects using both command and entmake.

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📚 What You’ll Learn

By the end of this lesson, you’ll be able to:

• Draw basic objects using AutoLISP: lines, circles, and rectangles
• Understand when to use command vs. entmake
• Use entmake to directly define geometry without user prompts
• Write reusable drawing routines with hardcoded or user-driven inputs

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🧠 Why It Matters

Creating geometry with AutoLISP opens the door to automating repetitive drawing tasks. Whether you’re laying out blocks, adding detail, or batch-generating entities, knowing how to build geometry in code gives you power and speed inside AutoCAD.

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🛠️ Tools You’ll Use

Tool / Function	Purpose
command	Invokes native AutoCAD drawing commands
entmake	Constructs and inserts objects directly from DXF data
getpoint	Collects coordinates from the user
list, quote	Constructs points and entity data

🧭 Lesson Structure

1️⃣ Using the command Function

The command function simulates manual AutoCAD commands. It’s simple and mirrors user input.

Draw a Line Between Two Points

(defun c:drawline ()
  (setq pt1 (getpoint "\nStart point: "))
  (setq pt2 (getpoint "\nEnd point: "))
  (command "LINE" pt1 pt2 "")
  (princ)
)

Draw a Circle at a Point

(defun c:drawcircle ()
  (setq center (getpoint "\nCenter point: "))
  (setq radius (getreal "\nRadius: "))
  (command "CIRCLE" center radius)
  (princ)
)

Draw a Rectangle Using Two Points

(defun c:drawrect ()
  (setq pt1 (getpoint "\nFirst corner: "))
  (setq pt2 (getpoint "\nOpposite corner: "))
  (command "RECTANGLE" pt1 pt2)
  (princ)
)

✅ Use the "" at the end of a command call to signal “Enter” or end of input.

2️⃣ Using entmake for DXF-Based Geometry

entmake allows you to create entities directly by supplying DXF group codes.

Draw a Line with Hardcoded Points

(entmake
  (list
    (cons 0 "LINE")
    (cons 10 (list 0.0 0.0 0.0)) ; Start point
    (cons 11 (list 100.0 100.0 0.0)) ; End point
  )
)

Group Code	Meaning	Example Value

0

Entity type

"LINE", "CIRCLE"

10

Start point

(list x y z)

11

End point

(list x y z)

40

Radius (CIRCLE)

25.0

Draw a Circle with entmake

(entmake
  (list
    (cons 0 "CIRCLE")
    (cons 10 (list 50.0 50.0 0.0))
    (cons 40 10.0)
  )
)

🧠 Use entmake when you don’t need user interaction and want full control.

3️⃣ Command vs. entmake – When to Use What

Approach	Pros	Use When
command	Simple, readable, supports dynamic input	Interacting with user or invoking full commands
entmake	Precise, no dialog boxes, script-friendly	Creating geometry programmatically or in bulk

✅ Lesson Checklist

Task	Completed
Drew a line, circle, and rectangle using command	☐
Created a circle and line using entmake	☐
Understood DXF group codes used with entmake	☐
Compared pros and cons of command vs. entmake	☐

📌 Quick Tips

Tip	Why It Helps
Always include all required DXF codes	Missing codes can cause invisible or bad entities
Use "" to finish command input	Simulates Enter in AutoCAD command stream
Wrap geometry in separate functions	Encourages reuse and debugging
Use command for flexibility, entmake for control	Match the method to the job

🧩 Real-World Applications

Use Case	Recommended Method	Why
Interactive line drawing	command	Allows real-time point selection
Title block layout tool	entmake	Fully automated and fixed layout
Batch geometry creation	entmake	Faster and avoids prompts
User-guided circle tools	command	Intuitive and readable for input

📁 Files and Resources

File / Resource	Description
draw_shapes_command.lsp	Routine using command to draw all 3 shapes
draw_shapes_entmake.lsp	Routine using entmake with DXF codes
entmake_reference.docx	DXF code cheat sheet for common geometry types

📖 Review Table

Function	Use Case	Example
command	Simulates AutoCAD command input	(command "LINE" pt1 pt2 "")
entmake	Creates entities from DXF list	(entmake (list (cons 0 "LINE") ...))
getpoint	Gets point from user	(getpoint "\\nStart point: ")
list	Create coordinate values	(list 0.0 0.0 0.0)
cons	Create key/value pair for DXF	(cons 10 (list x y z))