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stefan
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PostPosted: Tue Jul 04, 2017 1:16 pm    Post subject: Re: IFC and the Survey Point Object Reply with quote

AFAIK the Survey point may have "large" coordinates, but the actual survey point item is located in the relatively small local coordinate system of the project.

Revit has a 20by20km "box" in which everything should be placed (otherwise bad things happen).
ARCHICAD has certain limitations, but I read that it re-calculates the center of all placed objects and thus keeps all coordinates in a relatively confined area (unless you have two objects too far apart).

The whole reason of using the Survey point is to make the world coordinates known, without having to model everything in world coordinates.

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Brian Renehan
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PostPosted: Wed Jul 05, 2017 12:25 pm    Post subject: Re: IFC and the Survey Point Object Reply with quote

Hi Stephan

Thanks. I'd like a little more certainty.
I've linked a Zipped IFC file, pushed out of Revit 17.2 using MVD Coordination View 2.0. Link below:

https://www.dropbox.com/s/353uzbw4kdzbhv5/rac_basic_sample_project.zip?dl=0

The House origin (internal origin) is in the center of the house, however, the Survey point is using the Ifc Local Placement coordinates below. They would match the coordiantes of a building in Sydney Australia, using GDA94 Coordiantes.

Survey coordiantes should be - E:360,000m , N:6,500,000m, H:250m, rotation of 15 degrees.


#19= IFCDIRECTION((0.,0.,1.));
#31998= IFCCARTESIANPOINT((360000000.,6500000000.,0.));
#32000= IFCDIRECTION((0.965925826289068,-0.258819045102521,0.));
#32002= IFCAXIS2PLACEMENT3D(#31998,#19,#32000);
#32003= IFCLOCALPLACEMENT($,#32002);
#32004= IFCSITE('3lIj7B0LnBjf0mvxk2zve8',#41,'Surface:411452',$,'',#32003,#31996,$,.ELEMENT.,(42,12,46,799999),(-71,-2,0,-599999),250000.,$,$);

Do you mind opening the file in ArchiCAD, and see if it exhibits any of the below errors that files with large coordiantes can have?

It would be great if you SaveAs back as an ArchCAD 20+ IFC file, and we can round trip it twice.

Thanks and Cheers
Brian

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stefan
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Location: A castle in Belgium

PostPosted: Wed Jul 05, 2017 1:15 pm    Post subject: Re: IFC and the Survey Point Object Reply with quote

Many parameters which may interfere... The template which ARCHICAD uses when importing and the IFC Translator configuration. The main choice is if you'd load it for "editable import" or not. As this directly influences what type of elements you'd get: e.g. wall versus object or Morph (freeform static geometry).

You'd better ensure only the Finished Floor Levels are indicated (inside Revit) as "BuildingStorey" -- otherwise all levels become individual stories in the iFC export. I have 6 floors in this two-storey building
3. Roof Line
2. Level 2
1. Ceiling
0. Level 1
-1. Level 1 Living Rm
-2. Foundation

But let's focus on the Survey Point.

From the IFC file, I get following Site coordinates in the ARCHICAD Project Location
Latitude = 4212'46"
Longitude = -71-2'0"
Elevation = 250m
Project North 120

The ARCHICAD Project point (dark cross) is in the middle of the house.
I have no navigation issues (that we would expect with very large coordinates).

Exporting back to IFC reveals that the Site Coordinates are intact.
#8334= IFCSITE('3lIj7B0LnBjf0mvxk2zve8',#12,'Surface:411452',$,'',#63,#8329,$,.ELEMENT.,(42,12,46,799999),(-71,-2,0,-599999),250000.,$,#52);

Here is the export to compare

https://www.dropbox.com/s/c3f1t652c66nv07/rac_basic_sample_project_fromAC20_surveypt.ifc.zip?dl=0

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--- stefan boeykens --- architect-engineer-musician ---
ARCHICAD21/Revit2017/SketchUp2017/Cinema4D18/Rhino5/Unity5
rMBPTB15:i7Quad2.7Ghz+16GB+Radeon455/Sierra+Win10

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Brian Renehan
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PostPosted: Wed Jul 05, 2017 2:16 pm    Post subject: Re: IFC and the Survey Point Object Reply with quote

Thanks Stefan

Sorry for the dodgy levels. The file is a sample Out of the Box Revit file. I did not check the levels before export.

We lost the IfcLocalPlacement X & Y (asting and Northing) data on export:
#8334= IFCSITE('3lIj7B0LnBjf0mvxk2zve8',#12,'Surface:411452',$,'',#63,#8329,$,.ELEMENT.,(42,12,46,799999),(-71,-2,0,-599999),250000.,$,#52);
#56= IFCDIRECTION((0.965925826289,-0.258819045103,0.));
#58= IFCDIRECTION((0.,0.,1.));
#60= IFCCARTESIANPOINT((0.,0.,0.));
#62= IFCAXIS2PLACEMENT3D(#60,#58,#56);
#63= IFCLOCALPLACEMENT($,#62);

Thus the house came back into Revit 6,500 km from the internal origin. Height and Rotation to the true north were correct.

Other than, export to "at Project Origin" is there another way to save out the file. I will need to check back with my Peer I got to do the first round test with round tripping.

The more and more testing I do of IFC round tripping the more I believe zeroing out the IFCSite Elevation and IFCSice Local Placement is the best option for ensuring certainty.

Cheers and thanks
Brian

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