getGeomExtents creates wrong data

[ynapeu]

When I subtract a second cylinder from a cylinder, the GeomExtent increases. Can something like this happen?

The Original Zylinder has (-15,-15,0) (15,15,100) 

the Zylinder with the differenz Solid is 0.00015 greater.

[tbrammer]

Which AutoCAD version are you using? I tested with AutoCAD 2020 and 2024 like this:

• _SUBTRACT thin cylinder from tall cylinder
• _LIST for the resulting cylinder using LUPREC=8. 

The result is shown in screenshot below. It equals the bounding box of the initial cylinder for both versions.

(German version. "Untere/Obere Begrenzung" = "Lower/Upper Boundary", "Begrenzungsrahmen"="Boundary box")

I didn't test getGeomExtents() explicitly. 

Can you please check whether getGeomExtents() yields different results than _LIST shows?

[ynapeu]

Hello

The output from the list command is okay.

i use the following Code pEnt is the Solid

in Autocad 2022 the date will be okay, in Autocad 2024 i get some small differences.

AcDbExtents extents;

pEnt->getGeomExtents(extents);

AcGePoint3d amax;

amax = extents.maxPoint();

AcGePoint3d amin;

amin = extents.minPoint();

ads_printf(L"\nmax=%g,%g,%g  min=%g,%g,%g", amax.x, amax.y, amax.z, amin.x, amin.y, amin.z);

[tbrammer · Accepted solution]

On my system I get on both AutoCAD 2022 and 2024:

	Name	Value	Type
▶	maxpt	{x=15.000150220923764 y=15.000000000000000 z=100.00000000000000 }	AcGePoint3d

AcGeContext::gTol.equalPoint() is 1e-10.

AcGeContext::gTol.equalVector() is 1e-12.

0.00015 is several orders of magnitude larger than this. The ARX docs makes no statement about the exactness of getGeomExtents().  It would be interesting how AutoCAD calculates the dimensions that _LIST prints. Obviously the deviation should be visible with LUPREC=8.

If you need higher accuracy you could try to use the BREP API to analyze the 3DSOLID.

[ynapeu]

You are right, both (Autocad 2022 and Autocad 2024) get the same result.

Thanks for yor help, the BREP creates correct results.

AcBrBrep myrep;
myrep.set(*(AcDb3dSolid*)pEnt);
AcGeBoundBlock3d block1;
myrep.getBoundBlock(block1);
block1.getMinMaxPoints(amin, amax);
ads_printf(L"\nbrepmax=%g,%g,%g min=%g,%g,%g", amax.x, amax.y, amax.z, amin.x, amin.y, amin.z);

this will print the correct Bounding box.

brepmax=15,65,100 min=-15,35,0