Industrial basic IFC - extract model structure tree

First , I'm sorry , I haven't updated the article for a long time , It's too late to explain , Let's get straight to the point . This article is still connected with the previous excavation IFC series , Ahead Several articles We talked IFC Some of the concepts of 、 Data structures and visualization tools , With these mattresses , We can basically talk about some practical content , For example, how to use open source toolkit to read and write IFC data , This includes model structure tree data 、 Geometric data and attribute data .

So the theme of this article is to extract IFC Information of model structure tree , And based on IFC 4 edition , But yes IFC 2x3 Most of them are general . First, combine the picture pairs below IFC Make a description of the model structure tree ： In disassembly IFC There are two related entities involved in the process of structure tree ,IfcRelAggregates and IfcRelContainedInSpatialStructure, The former expresses spatial decomposition , For example, a building can be divided into multiple floors , Another example is that piers can be divided into bent caps 、 Columns 、 Bearing platform and pile foundation ; The latter expresses the elements in space , For example, there is a structural wall on the first floor 、 column 、 door 、 Windows, etc . In other words , We can divide elements into non spatial elements and non spatial elements , If you want to get the non spatial elements in the spatial elements, use IfcRelContainedInSpatialStructure, The rest is used IfcRelAggregates .

The Open Source Toolkit we use here is xBIM, It is oriented towards .NET Platform IFC tookit, The main development language is C#, Of course, the geometry library part is still based on C++ Mainly . If readers are used to using Python, It is also recommended that you use IfcOpenShell This library , The basic logic is almost the same .

IfcRelContainedInSpatialStructure

To get non spatial elements in spatial elements , First, we need to determine whether the current element is a spatial element IfcSpatialStructureElement, Then use the corresponding attribute of this class ContainsElements To get the element set .

var spaceEle = elem as IIfcSpatialStructureElement;
if (spaceEle != null)
{
    //using IfcRelContainedInSpatialElement to get contained elements
    var containedElements = spaceEle.ContainsElements.SelectMany(rel => rel.RelatedElements).ToList();
    for (int i = 0; i < containedElements.Count(); i++)
    {
        // do what you want
        
        //  Use recursion to complete the traversal of the structure tree 
    }
}

IfcRelAggregates

Subset elements of spatial decomposition can be represented by inverse attributes IsDecomposedBy obtain .

foreach ( var item in elem.IsDecomposedBy.SelectMany ( r => r.RelatedObjects ) )
{
    // do what you want
    
    //  Use recursion to complete the traversal of the structure tree 
}

Spatial element decomposition

IFC Have a semantic spatial structure tree , In a single file, a “ project IfcProject”, The project contains one or more “ site IfcSite”, The site also contains one or more “ Architecture IfcBuilding”, From building to floor , From floor to wall 、 plate 、 column . Of course, this is just a simple example , With IFC The gradual improvement and enrichment of Standards , Grading methods are also more and more diverse , For example, there can be routes in the site IfcAlignment, There are bridges IfcBridge wait .

Decomposition of non spatial elements

Composite elements IfcElementAssembly It is also a means of expression at the structural level , It can be further decomposed , For example, we take a standard segment of the bridge girder as a composite object , And it can be decomposed into roof 、 floor 、 Web 、 Stiffeners and other components .

Summary

In the actual coding process , We need to combine the above two structural divisions , And use recursive logic to traverse the complete structure tree .Ok, So much for that , Next up ：《 Industrial foundation — utilize xBIM extract IFC Geometric and attribute data 》. The following is what I created IFC Communication group , Those who are interested can scan the code to join ！