在三维空间中，我们可以通过使用SolidUtil下的ClosestPointToFace方法来求出点到曲面的投影。该函数只需要传入曲面（ISubEntity）和空间中的点坐标，就可以返回投影点坐标，空间点到投影点的法向量，以及uv参数。

void CloseestPointToFaceTest()
{
	ElementHandle ptEH(20594, ACTIVEMODEL);
	ElementHandle surfEH(20620, ACTIVEMODEL);

	CurveVectorPtr pCV = ICurvePathQuery::ElementToCurveVector(ptEH);
	DPoint3d spacePt;
	pCV->at(0)->GetStartPoint(spacePt);

	ISolidKernelEntityPtr body;
	SolidUtil::Convert::ElementToBody(body, surfEH);
	bvector<ISubEntityPtr> faces;
	SolidUtil::GetBodyFaces(&faces, *body);
	
	DPoint3d ptOnFace;
	DVec3d normal;
	DPoint2d param;
	SolidUtil::ClosestPointToFace(*faces[0], spacePt, ptOnFace, normal, param);
	
	DSegment3d segment = DSegment3d::From(ptOnFace, ptOnFace);
	ICurvePrimitivePtr  pCP = ICurvePrimitive::CreateLine(segment);

	EditElementHandle eeh;
	DraftingElementSchema::ToElement(eeh, *pCP, nullptr, ACTIVEMODEL->Is3d(), *ACTIVEMODEL);

	ElementPropertiesSetterPtr setter = ElementPropertiesSetter::Create();
	setter->SetColor(4);
	setter->SetWeight(7);
	setter->Apply(eeh);
	eeh.AddToModel();
}