IFC4x3 Alignment Geometry Implementation Guide

Richard Brice, PE

Forward

IfcAlignment, and the related geometric concepts, are new to the IFC4x3 specification. By virtue of expanding the IFC specification into the infrastructure domain, an entirely new audience is summoned into the buildingSmart community. I am one of those new arrivals.

The IFC specification is very technical and is written with an expectation that the reader has a high level of knowledge and experience with IFC. Being a technical specification, there is no hand-holding for the novice. Industry guidance documents are generally not available to assist those new to the infrastructure and alignment aspects of IFC4x3.

I set out to add alignment geometry support to the IfcOpenShell Toolkit. Being a bridge engineer, I am well versed in highway alignment geometry. I was completely overwhelmed and befuddled with alignment representations in the IFC specifications. Through a long and persistent struggle, I was able to figure out most all of what a developer needs to implement IFC alignment geometry in a software application.

This implementation guide captures what I have learned about IFC4x3 alignment geometry and provides guidance as to how a software developer may go about creating an implementation. I hope that other developers find this guide useful, because in the end, IFC is about interoperability. We all need a common understanding of the infrastructure alignment concepts and geometry.

Table of Contents

1. Introduction
2. Horizontal
3. Vertical
4. Cant
5. Locating a Point along an Alignment
6. Offset Curves
7. Linear Placement
8. Referents and Stationing
9. Precision and Tolerance