# WorldCoordinateSystem, IfcMapConversion and IfcSite

**URL:** <https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924>\
**Category:** Developers\
**Tags:** ifc4, ifc4-errata\
**Created:** [October 18, 2019, 12:59pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924 "2019-10-18T12:59:08Z")\
**Posts on this page:** 14\
**Page:** 1

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**Author:** ![skogsholm](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/skogsholm/32/648_2.png) [@skogsholm](https://forums.buildingsmart.org/u/skogsholm)\
**Post date:** [October 18, 2019, 12:59pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/1 "2019-10-18T12:59:08Z")

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I have trouble interpreting how values in WorldCoordinateSystem will move&rotate objects in IFC when combined with IfcMapConversion.  
To visualise, I made a diagram showing the relations.  
Assuming my interpretation of WorldCoordinateSystem is correct, should RefLatitude/RefLongitude point to (A) or (C) in the attached picture?? See the yellow comment.  
.

 ![image](https://us1.discourse-cdn.com/flex016/uploads/buildingsmart1/original/1X/b1993655555e0d581ce071577c0131c5a7392089.png)

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**Author:** ![stefkeB](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/stefkeb/32/1755_2.png) [@stefkeB](https://forums.buildingsmart.org/u/stefkeB)\
**Post date:** [October 18, 2019, 7:03pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/2 "2019-10-18T19:03:52Z")

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[https://thinkmoult.com/ifc-coordinate-reference-systems-and-revit.html](https://thinkmoult.com/ifc-coordinate-reference-systems-and-revit.html)

@Moult made a good explanation. There is some redundancy between having a mapping and also storing the Lat/Long mostly for backward compatibility.

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**Author:** ![TLiebich](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/tliebich/32/71_2.png) [@TLiebich](https://forums.buildingsmart.org/u/TLiebich)\
**Post date:** [October 18, 2019, 9:58pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/3 "2019-10-18T21:58:54Z")

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in addition to the great explanations by @Moult, and to come back to your actual questions - the answer should be “C”. The RefLatitude and RefLongitute shall be used (as documented for [IfcSite](https://standards.buildingsmart.org/IFC/RELEASE/IFC4/ADD2_TC1/HTML/link/ifcsite.htm))

> If asserted, the _Longitude_ , _Latitude_ and _Elevation_ establish the point in WGS84 where the point 0.,0.,0. of the _LocalPlacement_ of IfcSite is situated.

This is however redundant to applying the local placement of the site to the geographic reference point as established by _IfcMapConversion_. The attributes RefLatitude, RefLongitute and RefElevation are mainly there due to backward compatibility with earlier versions of the IFC Schema. When using _IfcMapConversion_, those values should not be used for geo referencing.

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**Author:** ![ReD\_CoDE](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/red_code/32/226_2.png) [@ReD\_CoDE](https://forums.buildingsmart.org/u/ReD_CoDE)\
**Post date:** [October 19, 2019, 10:38am UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/4 "2019-10-19T10:38:00Z")

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Also take a look at this post:

> [@Coordinates of the IfcLocalPlacement/IfcCartesianPoint](https://forums.buildingsmart.org/t/coordinates-of-the-ifclocalplacement-ifccartesianpoint/1809):
>
> do you know what is best practice on defining the coordinates of components in the IFC Structure, respectively the IfcLocalPlacement/IfcCartesianPoint? Depending whether the component sits near the Project Zero Point the values appearing in the IfcCartesianPoint will be in a range of some tens of meters. When the model georeferenced acording to a local datum, the component sits in the BIM Authoring tool far away from the Project Zero Point resulting in coordinates rangin in thousends/millions. …

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**Author:** ![skogsholm](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/skogsholm/32/648_2.png) [@skogsholm](https://forums.buildingsmart.org/u/skogsholm)\
**Post date:** [October 21, 2019, 9:50am UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/5 "2019-10-21T09:50:59Z")

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> [@TLiebich](#):
>
> 0.,0.,0. of the _LocalPlacement_ of IfcSite

Yes, and this is the reason for my post.  
“0.,0.,0. of the LocalPlacement of IfcSite”: Does this mean point B) or C) in the diagram where IfcSite (C ) is located at [196.0, 387.0, 0.0]?

```
#8=IFCSITE('<guid>',#2,'Site',$,$,#34,$,$,.ELEMENT.,(58,44,40,04562),(5,38,57,37631),31.,'',$);
#34=IFCLOCALPLACEMENT($,#48)
#48=IFCAXIS2PLACEMENT3D(#55,#56,#57);
#55=IFCCARTESIANPOINT((196.0,387.0,0.));
#56=IFCDIRECTION((0.,0.,1.));
#57=IFCDIRECTION((1.,0.,0.));

```

(@Moult has reviewed my diagram earlier this year, but did not comment on this possible error)

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**Author:** ![TLiebich](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/tliebich/32/71_2.png) [@TLiebich](https://forums.buildingsmart.org/u/TLiebich)\
**Post date:** [October 21, 2019, 12:34pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/6 "2019-10-21T12:34:58Z")

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good point, the sentence of “0.,0.,0. of the LocalPlacement of IfcSite” can indeed be misinterpreted. But what is meant is:

0., 0. ,0. (the origin) within the object coordination system of IfcSite, that is established by IfcLocalPlacement with an offest/rotation relative to the project coordinate system.

That would still be _C_

The spec should better read

> If asserted, the _Longitude_ , _Latitude_ and _Elevation_ establish the point in WGS84 where the origin of the object coordinate system of _IfcSite_ is situated.

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**Author:** ![agron](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/agron/32/1158_2.png) [@agron](https://forums.buildingsmart.org/u/agron)\
**Post date:** [October 23, 2019, 9:29pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/7 "2019-10-23T21:29:45Z")

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Dear gentlemen,  
The industry needs a proper guideline for this puzzle so everyone knows that the answer is “C”. The best would be to see this as an ISO Standard, but until this happens an official bsI guideline would do just fine. The reason is that we will see more and more issues concerning the coordination of models. So the guideline will solve many open issues that we usually have at many kick off meetings in BIM projects.

Isn’t @Moult working with someone in this direction?

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**Author:** ![Moult](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/moult/32/196_2.png) [@Moult](https://forums.buildingsmart.org/u/Moult)\
**Post date:** [October 24, 2019, 8:57pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/8 "2019-10-24T20:57:48Z")

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Thanks for the explanation @TLiebich!

I absolutely agree that it is confusing. I am sorry to say that I am not working with anyone on this currently.

However, it is on my to-do list to build a little utility which will do things like:

1. Report coordinates
2. Replace coordinates
3. Convert coordinates

It will be a free and open-source tool, which hopefully we can all use to verify and correct model coordinate behaviours once we have all tested it and double and triple checked the behaviour 🙂

I believe a little tool, plus perhaps a bit of rewording in the IFC spec docs, can help resolve this over time. It’s good to see IFC mature!

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**Author:** ![Hans\_Lammerts](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/hans_lammerts/32/835_2.png) [@Hans\_Lammerts](https://forums.buildingsmart.org/u/Hans_Lammerts)\
**Post date:** [October 27, 2019, 7:52pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/9 "2019-10-27T19:52:09Z")

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Dion, there is one initiative from the dutch academic university that could be of interest.

In civil design we have many challenges (on projects) for aligning ifc files to national grid or even project grids. Tools that make things easier have high demands!

> **[tudelft3d/IfcLocator](https://github.com/tudelft3d/IfcLocator)**
>
> Contribute to tudelft3d/IfcLocator development by creating an account on GitHub.

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<div class="post-metadata">

**Author:** ![ReD\_CoDE](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/red_code/32/226_2.png) [@ReD\_CoDE](https://forums.buildingsmart.org/u/ReD_CoDE)\
**Post date:** [October 27, 2019, 8:43pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/10 "2019-10-27T20:43:16Z")

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Thanks Hans,  
It sounds interesting, especially when I see “Cesium”

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**Author:** ![Hans\_Lammerts](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/hans_lammerts/32/835_2.png) [@Hans\_Lammerts](https://forums.buildingsmart.org/u/Hans_Lammerts)\
**Post date:** [October 27, 2019, 9:35pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/11 "2019-10-27T21:35:41Z")

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Dion, When i use Blender i get this error messages. I tried 2.80 but it said “needs updating” This message i get when 2.78 is installed. I want to test your tools with some of my CAD models/geometry from Inventor and DWG. / step. Geometry made to IFC in various ways with various aspects like CRS / Color and ‘Block definitions’ Could you help me with this?

 ![blender%20error](https://us1.discourse-cdn.com/flex016/uploads/buildingsmart1/original/1X/71c17a0a95200ca8d991017b5b0fe6d28bc21684.png)

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**Author:** ![Hans\_Lammerts](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/hans_lammerts/32/835_2.png) [@Hans\_Lammerts](https://forums.buildingsmart.org/u/Hans_Lammerts)\
**Post date:** [October 27, 2019, 9:38pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/12 "2019-10-27T21:38:56Z")

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Ehsan, i really think our (… hate the word…) [AEC design industry] is getting way to much ‘layers of software’ to use. If its not yearly versions of your favorite ‘BIM authoring tools’ its all the addons and support that will maken to much dependancies for IFC and other open formats.

Get it to work and without a doubt …you will know next year it will be different and probably will not work anymore.

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**Author:** ![Moult](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/moult/32/196_2.png) [@Moult](https://forums.buildingsmart.org/u/Moult)\
**Post date:** [October 27, 2019, 10:03pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/13 "2019-10-27T22:03:55Z")

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Hey @Hans_Lammerts - it looks as though you have got Blender 2.7\* installed. It requires Blender 2.8\*.

It would be good if you could join the IRC chat - I will be able to help you live: [https://blenderbim.org/community.html](https://blenderbim.org/community.html)

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**Author:** ![Hans\_Lammerts](https://sea2.discourse-cdn.com/flex016/user_avatar/forums.buildingsmart.org/hans_lammerts/32/835_2.png) [@Hans\_Lammerts](https://forums.buildingsmart.org/u/Hans_Lammerts)\
**Post date:** [October 27, 2019, 10:36pm UTC](https://forums.buildingsmart.org/t/worldcoordinatesystem-ifcmapconversion-and-ifcsite/1924/14 "2019-10-27T22:36:11Z")

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Thanks! Sorry to post it here as sidenote. We will be in touch!