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Implements default direction of IfcAxis2PlacementLinear.Axis and RefDirection #8145

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Implements default direction of IfcAxis2PlacementLinear.Axis and RefDirection #8145

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0ec895f
uses axis direction from curve evaluation when Axis is not provided
RickBrice May 29, 2026
b75a689
Updates IfcAxis2PlacementLinear and matrix4::init per @aothms suggest…
RickBrice Jun 10, 2026
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27 changes: 7 additions & 20 deletions src/ifcgeom/mapping/IfcAxis2PlacementLinear.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -29,53 +29,40 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcAxis2PlacementLinear* inst)
Logger::Error(std::runtime_error("Location must be IfcPointByDistanceExpression for IfcAxis2PlacementLinear"));
}

Eigen::Vector3d o, axis(0, 0, 1), refDirection;

taxonomy::matrix4::ptr m = taxonomy::cast<taxonomy::matrix4>(map(inst->Location()));
o = m->components().col(3).head<3>();
Eigen::Vector3d o = m->components().col(3).head<3>();

// From 8.9.3.4 IfcAxis2PlacementLinear there are 4 cases that need to be considered
// 1) Axis is given but not RefDirection
// 2) RefDirection is given but not Axis
// 3) Neither Axis or RefDirection are provided
// 4) Both Axis and RefDirection are provided
// When Axis or RefDirection are not provided explicitly in the IfcAxis2PlacementLinear,
// they are taken from the context of curve by evaluating the Location, which is an IfcPointByDistanceExpression on a curve.
// The curve tangent is used as RefDirection and the curve normal is used as Axis.

const bool hasAxis = inst->Axis() != nullptr;
const bool hasRef = inst->RefDirection() != nullptr;

/*
if (hasAxis != hasRef) {
Logger::Warning("Axis and RefDirection should be specified together", inst);
}
*/

Eigen::Vector3d axis, refDirection;
if (hasAxis && !hasRef) {
taxonomy::direction3::ptr a = taxonomy::cast<taxonomy::direction3>(map(inst->Axis()));
axis = *a->components_;

refDirection = m->components().col(0).head<3>(); // RefDirection is the curve tangent when omitted
// refDirection is not necessarily orthogonal to axis.
// axis.cross(refDirection) gives y. y.cross(axis) gives x=refDirection
refDirection = axis.cross(refDirection).cross(axis);
} else if (!hasAxis && hasRef) {
taxonomy::direction3::ptr r = taxonomy::cast<taxonomy::direction3>(map(inst->RefDirection()));
refDirection = *r->components_;
Eigen::Vector3d up(0, 0, 1);
axis = refDirection.cross(up.cross(refDirection));
axis = m->components().col(2).head<3>(); // Axis is the curve normal when omitted
} else if (!hasAxis && !hasRef) {
refDirection = m->components().col(0).head<3>(); // RefDirection is the curve tangent when omitted
Eigen::Vector3d up(0, 0, 1);
axis = refDirection.cross(up.cross(refDirection));
axis = m->components().col(2).head<3>(); // Axis is the curve normal when omitted
} else {
taxonomy::direction3::ptr a = taxonomy::cast<taxonomy::direction3>(map(inst->Axis()));
axis = *a->components_;

taxonomy::direction3::ptr r = taxonomy::cast<taxonomy::direction3>(map(inst->RefDirection()));
refDirection = *r->components_;
refDirection = axis.cross(refDirection).cross(axis); // refDirection needs to be orthogonal to axis
}

// axis and refDirection need to be orthogonal
return taxonomy::make<taxonomy::matrix4>(o, axis, refDirection);
}

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48 changes: 34 additions & 14 deletions src/ifcgeom/taxonomy.h
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Expand Up @@ -277,20 +277,40 @@ typedef item const* ptr;
struct IFC_GEOM_API matrix4 : public item, public eigen_base<Eigen::Matrix4d> {
private:
void init(const Eigen::Vector3d& o, const Eigen::Vector3d& z, const Eigen::Vector3d& x) {
auto Z = z.normalized();
auto Y = Z.cross(x).normalized();
auto X = Y.cross(Z);
components_ = new Eigen::Matrix4d;
(*components_) <<
X(0), Y(0), Z(0), o(0),
X(1), Y(1), Z(1), o(1),
X(2), Y(2), Z(2), o(2),
0, 0, 0, 1.;
if (is_identity()) {
// @todo detect this earlier to save us the heapalloc.
delete components_;
components_ = nullptr;
tag = IDENTITY;
auto valid_and_non_zero_extent = [](const Eigen::Vector3d&v,double eps = 1.e-9) {
return v.allFinite() && v.squaredNorm() > eps*eps;
};

// check z and x are valid vectors
if (!valid_and_non_zero_extent(z) || !valid_and_non_zero_extent(x)) {
throw std::runtime_error("Invalid during for matrix4 construction");
}

auto Z = z.normalized(); // ensure Z is a unit vector
auto Y = Z.cross(x); // Y is orthogonal to x and Z

// make sure Y is a valid vector
if (!valid_and_non_zero_extent(Y)) {
throw std::runtime_error("Parallel or degenerate matrix4 construction");
}

Y.normalize(); // ensure Y is a unit vector
auto X = Y.cross(Z); // X is orthogonal to Y and Z, and a unit vector

// check if this is going to be an identity matrix
double eps = 1.e-9;
if (X.isApprox(Eigen::Vector3d(1., 0., 0.), eps) &&
Y.isApprox(Eigen::Vector3d(0., 1., 0.), eps) &&
Z.isApprox(Eigen::Vector3d(0., 0., 1.), eps) &&
o.isApprox(Eigen::Vector3d(0., 0., 0.), eps)) // in the full 4x4 matrix, this will be (0,0,0,1)
{
tag = IDENTITY;
} else {
components_ = new Eigen::Matrix4d;
(*components_) << X(0), Y(0), Z(0), o(0),
X(1), Y(1), Z(1), o(1),
X(2), Y(2), Z(2), o(2),
0, 0, 0, 1.;
}
}
public:
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