How to use Inkscape’s Geometric Construction Tool

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We are about to delve into a topic that I have little to no experience in, CAD Drawing. When envisioning CAD Drawing, think of architectural designs and product diagrams. In the wonderful world of Inkscape, the upcoming version 1.2 (as of writing I’m using version 1.2 Beta), we have an odd little tool labeled Do geometric constructions. This tool is designed to simulate basic CAD tools for precision drawing. For the sake of this article, I will refer to this tool as the Geometric Construction Tool.

My goal for this article is to give you a brief idea of how the Geometric Constructions Tool works and to provide you with online sources that will provide you with more information.

Quick-Click Table of Contents

Geometric Construction Tools

Mirror Symmetry Settings

Introduction to the Geometric Construction Tool

The Geometric Construction Tool isn’t a single tool, but a series of tools for all of your geometric and technical drawing needs. You’ll find these tools in Inkscape’s Tool Settings bar, at the top of your window.

Need to Know

It will be to your benefit to enable snapping by either clicking on the Magnet icon on the far right end of Inkscape’s Tool Settings bar or using the keystroke Shift 5. (Not the 5 key on your keypad.)

Since the Geometric Construction Tool leverages the Path Effects feature in Inkscape, you will need to open the Path Effects Palette. To bring it up, click on the downward arrow located in the upper right-hand corner of your dock and select Path Effects within the Advanced group.

As a word of warning, as version 1.2 Beta, the Geometric Construction tool doesn't play nice with any pathes or objects on the same layer. This maybe due to the live path effects. That's just a guess. To reduce frustration, either avoid clicking on another path while using this tool or create a new layer for your next geometric construction and lock all other layers to avoid any interaction. I'm not saying that you can't have multiple objects created by the Geometric Construction tool on the same layer. But you will have to avoid creating objects on top of other objects.

On the opposite end of the Tool Settings bar, the button with the X icon is selected by default. This means that no geometric tool is active. You’ll only be able to select paths and objects.

Line Segment Tool

The Line Segment Tool basically creates line segments. Now you may be thinking, “Well heck, I could already do line segments with the Pen/Bezier Tool!” That’s true, but with the Line Segment tool, you can expand your line and have it cleanly cut off at the edge of the document. The path effect will easily modify itself as you drag it around the document using the Node tool.

To use the Line Segment Tool, have it selected in the Tool Settings at near the top of your screen. Plot your points using the left mouse button. You can hold the Ctrl button to constrain the line segment.

An animation of he line segment being created using the Geometric Construction Tool
An animated demo of the Line Segment Tool.

As of writing, Inkscape 1.2 Beta is still buggy. When a line segment doesn’t want to complete or it’s acting like it wants to create an additional segment, press the Return button. After creating your first point, the keystroke Shift – Return will create a vertical segment base upon when your cursor is located.

Circle by 3 Points

The Circle by 3 Points Tool creates new circles based on the locations of the three points you plot. With the Node Tool, you can adjust the size of the new circle.

An animation demoing the circle by 3 points using Geometric Construction Tool in Inkscape.
An animated example of how to create circles using the Circle by 3 Points tool.

Circle by Center and Radius

Circle by Center and Radius tool will let you create a circle by plotting two points for the center and radius. The Node tool can be used to adjust the size.

inkscape circle by center and radius tool
Demo of Circle by Center and Radius tool

Parallel Tool

The Parallel tool allows you to create parallel lines. You can adjust the distance using the Node tool. The Path Effects palette allows you to tweak the Offset and Length of your new parallel line.

Animation demoing how to create a parallel line using Geometric Construction Tool.
How to create parallel lines using the Geometric Construction Tool

Perpendicular Bisector

The Perpendicular Bisector tool lets you create perpendicular lines between two points. The length can be adjusted via the Path Effects pallet.

Angle Bisector

The Angle Bisector tool is another means of creating lines at a 45-degree angle. You’ll use three points in a triangular fashion, ideally plotting out a corner.

A demo of the Angle Bisector via theGeometric Construction Tool

Mirror Symmetry

Mirror Symmetry Tool allows you to create a new path, with two or more nodes and mirrors that path based on the settings in the Paths Effects Palette. (These settings alone deserve their own tutorial.) If you want to create more duplicates, click the Add Path Effect button (symbolized by a plus symbol in the Path Effects palette).

An example of using the Mirror Symmetry tool from the Geometric Construction Tool set.
A demo of the Mirror Symmetry tool in use.

Mirror Symmetry Settings

Let’s dig around in the Mirror Symmetry settings. There is a lot to learn.

Mode:

Freely Defined Mirror Line

This mode provides three nodes that run vertically. The middle node allows you to drag around the duplicates horizontally. The top and bottom nodes allow you to pivot the duplicates based on the position of the opposite node. Once you pivot, Inkscape will allow you to use the middle node to move duplicates up and down.

A demonstration of the adjustments that you can make while in Freely Defined Mirror Mode, while using Mirror Symmetry Effect.

Horizontal Page Center

The Horizontal Page Center mode takes your duplicates and flips them vertically. It also creates a set of three nodes that run horizontally to show the horizontal center of the page

Between the original square (bottom) and the duplicate (on top) lays the three nodes that make up the horizontal center of the page. (The guide that I laid there.)

Vertical Page Center

This mode will flip your duplicate horizontally based on the vertical center of your document’s page. The nodes created don’t do anything other than define the center of your page.

While using the Geometric Construction Tool, the Vertical Page Center Mode creates three nodes that run vertically, dividing the page.
With the Geometric Construction Tool selected, the Vertical Page Center Mode creates three nodes that run vertically down the center of the page, dividing it in half. (I added the guide that the nodes sit on.)

X Coordinate of Mirror Line Midpoint

This mode will flip your duplicates across horizontally. You’ll also find a set of nodes that run vertically. Click and drag the middle node to shift the duplicate path towards or from the center of your original path.

X Coordinate of Mirror Line Midpoint demo.

Y Coordinate of Mirror Line Midpoint

This next mode will flip your duplicates vertically. When enabling this mode, a set of three nodes will appear. Click and drag the middle node will shift your duplicate vertically.

Y Coordinate of Mirror Line Midpoint creates duplicates based upon the center of your object.

Other Path Effect Options:

Below the Mode settings are a set of checkboxes that further manipulate your duplicates. We’ll explore them.

Discard Original Path:

When checked, your original path vanishes, but the duplicate will remain. This is non-destructive.

Selecting Discard Original Path will cause your original path to disappear.
Before and after Discard Original Path is selected. The question mark was where the original path was.

Fuse Paths:

Selecting this checkbox will take two intersecting paths and create a corner where they meet. (See the animation below.)

Appling the Fuse Paths effect to a path that is mirrored

The Fuse Paths option will visually merge two objects as you bring them together. (See the animation below.)

Fuse Opposite Sides:

If your path has a fill and you overlap it with its duplicate, a hole will be created where they overlap. When Fuse Paths is also selected, the inverse of the overlap will be merged.

Split Elements:

When Split Elements is selected, both the original path and its duplicate can now how its own path effect(s), fill, and/or stroke. Split Elements won’t allow you to directly manipulate the path of the duplicate. You’ll need to select the right path effect to manipulate the size, shape, etc of the duplicate.

Split Elements allow to manipulate a duplicate's color, stroke, and shape.
In the example above the green duplicate uses a different stroke, different fill, and two different path effects.

The hint says, “Link styles on split mode”. What are “link styles”? Well, those are your fill, stroke, and path effects. “Split mode” is a reference to Split Elements. Whenever you have Split Elements checked, you can independently edit the fill, stroke, and path effects of your duplicate. Link Styles will force your duplicate to have the same fill, stroke, and path effects as your original path.

One More Note About Do Geometric Constructions

I just want to reinforce the fact that as of writing, Inkscape 1.2 is currently in beta. So this tutorial on the Geometric Construction Tool may or may not be updated and/or tweaked with either an upcoming update or the final release. I will try my best to keep this article updated following any changes.

References:

Below is a list of online resources that go into further depth on the Geometric Construction tool:

Upated: Apr 27, 2022