The Geometry Essentials Collection

Houdini Geometry Essentials 08

Procedural Selections: Groups


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3 hours 33 minutes


45 video tutorials in 4K 


Fraser Shiers


Houdini 19.5 + 20


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Part of the Houdini Made Easy series and Geometry Essentials Collection

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What You’ll Learn

When it comes to procedural modelling, making the right selections is the hardest part, demanding every trick and technique in the book. Here, we'll give you the skills you need, providing a deep knowledge of Houdini’s procedural selection toolkit - the mighty Group SOPs. Soon, you’ll be generating procedural hard surface models with ease, plus you’ll have a stack of techniques you can use in FX and MoGraph workflows to boot!

By the end of this course, you’ll have a deep understanding of:

  • All the essentials Group SOPs
  • The procedural counterparts to the interactive selection techniques covered in Geometry Essentials 07
  • Using group syntax to make procedural selections directly in group parameters
  • Using connectivity groups and connectivity attributes to define selection regions
  • Combining grouping techniques to make complex procedural selections
  • The best practice selection workflows for effective procedural modelling

Course Syllabus

Let’s talk details

Section 01

Procedural selection fundamentals

Solid foundations - where else would a Hipflask course start? In this first section, we’ll show you the procedural counterparts of the interactive selection techniques you use every day - grouping by region, combining groups and converting groups from one type to another.


1. Group Create SOP - Base Group
2. Group Create SOP - Keep in Bounding Regions
3. Group Promote SOP
4. Group Create SOP – Initial Merge
5. Group Create SOP - Group Name vs Base Group
6. Group Combine SOP

6 Tutorials   32 Minutes

Section 02

Output Groups

If there was ever a magic bullet for procedural selections, it's Output Groups - they're easy, powerful and dependable. You’ll be using them in the field as we take a procedural approach to a hard surface modelling exercise you first encountered in Geometry Essentials 07.


1. Output Groups
2. Practical exercise: hard surface circular indents - procedurally pt.1
3. Practical exercise: hard surface circular indents - procedurally pt.2

3 Tutorials   17 Minutes

Section 03

Loops, rings and expanding selections

Have you ever made a model without selecting loops and rings of edges? How about without growing and shrinking selections? No, us neither. Here, we’ll show you how to make those crucial types of selections procedurally.


1. Group Expand SOP - growing, shrinking and flood-filling selections
2. Group Expand SOP - constraining expansion using collision groups
3. Group Find Path SOP - finding paths through and between components
4. Group Find Path SOP - selecting full loops and rings of components

4 Tutorials   17 Minutes

Section 04

Hard surface hoses - procedurally

It's time to take your new procedural selection skills for a spin. In Geometry Essentials 07, you mastered hard surface modelling interactively; now, it’s time to tackle another of the same challenges procedurally. You’ll be pulling together all the techniques you’ve learnt so far to get this one over the line.


1. Practical exercise: hard surface hose - procedurally pt.1
2. Practical exercise: hard surface hose - procedurally pt.2
3. Practical exercise: hard surface hose - procedurally pt.3

3 Tutorials   20 Minutes

Section 05

Grouping by normals

Who’d have guessed we’d be talking about Normals again? They’re the driving force behind so many things in Houdini, and procedural selections are no different. Here, we’ll show you all the different ways you can use Group SOPs to select components based on their direction.


1. Group Create SOP - Keep by Normals
2. Combining Select by Normals with Base Group expressions
3. Grouping components which face away (backface) from the camera
4. Group Expand SOP - Restrict by Normal
5. Grouping by primitive angle
6. Grouping by edge angle
7. Grouping by edge angle on meshes vs curves
8. Grouping by primitive angle on more complex geometry
9. Group Create SOP - Include by Edges adds to the other selection types

9 Tutorials   35 Minutes

Section 06

Comparing group workflows

There are often multiple ways of making the same selection. Here, we'll compare two different workflows. Along the way, you'll discover new techniques, concepts and shortcuts, such as using group pattern syntax to make procedural selections directly in group parameters.


1. Procedural duct builder exercise intro - using output groups
2. Grouping edges by length
3. Grouping the first and last points on curves
4. Group syntax - excluding from selections
5. Using Output Groups rather than Group SOPs

5 Tutorials   22 Minutes

Section 07

Grouping by range

The group by range SOP is one of those nodes worth getting to know very well. It's the procedural equivalent of an interactive pattern selection, only much more powerful. We’ll show you how to use it to group all kinds of things, including curve endpoints, point and primitive loops, component percentages, and more.


1. Group by Range SOP - Range Filter and component sorting
2. Group by Range SOP - Range Type
3. Group by Range SOP - Connectivity
4. Grouping by range from existing groups and working with ordered groups
5. Grouping by percentage
6. Intrinsic attributes
7. Using the opinputpath() function

7 Tutorials   34 Minutes

Section 08

Procedural project time

You've learned a ton of procedural selection techniques, it's time to put them to the ultimate test. In this final section, we’ll build a procedural system to create hard surface and destruction-ready models with good topology for subdivision. Sound like a challenge? Don’t worry; you’ll know all you need by the time you get here.


1. Exercise intro and grouping U edge loops
2. Propagating groups during curve modelling operations
3. Counting the number of points on an edge loop
4. Grouping V edge loops and generating separate pieces
5. Intersecting groups to generate specific selections
6. Subdivision - creating hold edges procedurally
7. Overcoming edge group limitations
8. Modifying groups using combine operations

8 Tutorials   35 Minutes

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Geometry Essentials

Procedural Selections: Groups


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