axiolid_evaluate/

station.rs

//! Stations: a position at a distance along a curve, framed by the curve's
//! section (#241, ADR 0082).
//!
//! A station names a place by a measure along a basis curve instead of by
//! coordinates, the way an alignment is staked out. Reading it back is
//! curve evaluation, so it lives here, beside the arc-length machinery it
//! reuses ([`crate::arc_parameter`]).
//!
//! # Distance convention
//!
//! The distance is measured in the basis curve's own convention, from its
//! start:
//!
//! - an [`Elevated3`](axiolid_curve::Elevated3) or a
//!   [`Banked3`](axiolid_curve::Banked3) is authored against PLAN distance,
//!   its own parameter, and a station on it is a plan distance (the
//!   curve-evaluation contract's `DistanceConvention::PlanDistance`);
//! - every other curve, 2D or 3D, is measured by its arc length (for a 2D
//!   curve, the plan length).
//!
//! The start is parameter `0` for a line, a circle, an ellipse, an
//! intrinsic curve and a chain, and the first parameter of the domain for
//! a polyline or a B-spline. A distance must lie in `[0, L]`, `L` the
//! curve's length ([`station_length2`], [`station_length3`]): one full turn
//! for a closed conic, no limit for a line. A negative or non-finite
//! distance, and one past `L` by more than
//! [`ARC_LENGTH_TOLERANCE`]` * max(1, L)`, is refused by name; one past it
//! by less is read at `L`.
//!
//! # Section frame
//!
//! [`SectionFrame`] carries the point and three unit axes: `tangent` along
//! the curve, `lateral` to the LEFT of it, and `up = tangent x lateral`.
//!
//! - A 2D curve lies in the plane `z = 0`: `lateral` is the left normal,
//!   `up` is `+Z`.
//! - A [`Banked3`](axiolid_curve::Banked3) is framed by its rolled section
//!   ([`crate::banked::banked_section`]): `lateral` towards the left rail
//!   head.
//! - Every other 3D curve, an [`Elevated3`](axiolid_curve::Elevated3)
//!   included, gets the reference-up frame against `+Z`, the one
//!   `ReferenceCurveEvaluator::frame_at` returns: `lateral` is horizontal,
//!   `up` leans back with the grade. A vertical tangent has no such frame
//!   and is refused by name.
//!
//! [`SectionFrame::frame`] returns the axes in the curve-evaluation
//! provider's layout: `x` the tangent, `y` up, `z = -lateral` (to the
//! right). The contract's documentation of `frame_at` still says `z` is up
//! (#242); this module follows the provider.
//!
//! [`SectionFrame::plan`] is the vertical alternative: the tangent's
//! horizontal projection, the horizontal left normal and `+Z`, with grade
//! and bank dropped.
//!
//! # Explicit orientation (#246)
//!
//! [`SectionFrame::oriented`] turns a section frame by an explicit axis and
//! reference direction given as components in that frame, `(tangent,
//! lateral, up)`, not in world coordinates: a linear placement's axes "are
//! relative to the curve used for linear referencing ..., maintaining the
//! relationship to the tangent of the curve" (buildingSMART IFC 4.3,
//! `IfcAxis2PlacementLinear`), whose local `X`, `Y`, `Z` are the tangent,
//! the left lateral and up. The axis is the oriented up, exact; the
//! reference direction is made perpendicular to it (Gram-Schmidt, axis
//! primary) and becomes the oriented tangent. The point does not move.
//!
//! # Accuracy contract
//!
//! The point and frame are the exact curve's at a measure within
//! [`ARC_LENGTH_TOLERANCE`]` * max(1, s)` of `s` where the arc length is
//! numerical (a conic, a polyline is exact, a B-spline), at `s` itself on a
//! line, an intrinsic curve, a chain and an elevated or banked curve (their
//! parameter is the measure), each evaluated to its own stated accuracy
//! (Gauss-Legendre quadrature for intrinsic positions, ADR 0060).

use axiolid_contracts::{GeomError, GeomResult};
use axiolid_core::{Frame3, Point3, Scalar, Vec3};
use axiolid_curve::{Curve2, Curve3};

use crate::arc_parameter::{
    arc_length2, arc_length3, parameter_at_arc_length2, parameter_at_arc_length3,
    ARC_LENGTH_TOLERANCE,
};
use crate::curve::{derivative2, derivative3, domain2, domain3, evaluate2, evaluate3};

/// Largest sine of the angle between an orientation's axis and reference
/// direction that still counts as parallel ([`SectionFrame::oriented`]);
/// the graph refuses the same pairs when a station is pushed.
pub const ORIENTATION_TOLERANCE: Scalar = 1e-9;

fn invalid(detail: String) -> GeomError {
    GeomError::InvalidInput(detail)
}

/// A point on a curve and the section axes there: tangent, left lateral
/// and up, unit and right-handed (`up = tangent x lateral`).
#[non_exhaustive]
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct SectionFrame {
    /// The curve point.
    pub point: Point3,
    /// Unit tangent, in the direction of increasing distance.
    pub tangent: Vec3,
    /// Unit lateral axis, to the left of the tangent.
    pub lateral: Vec3,
    /// Unit section up, `tangent x lateral`.
    pub up: Vec3,
}

impl SectionFrame {
    /// The point offset from this frame's point: `lateral` along the
    /// lateral axis (positive to the left), `vertical` along up and
    /// `longitudinal` along the tangent.
    #[must_use]
    pub fn place(&self, lateral: Scalar, vertical: Scalar, longitudinal: Scalar) -> Point3 {
        self.point + lateral * self.lateral + vertical * self.up + longitudinal * self.tangent
    }

    /// The same point framed vertically: the tangent's horizontal
    /// projection, the horizontal left normal and `+Z`. Grade and bank are
    /// dropped.
    ///
    /// # Errors
    ///
    /// A vertical tangent, which has no horizontal projection.
    pub fn plan(&self) -> GeomResult<Self> {
        let horizontal = Vec3::new(self.tangent.x, self.tangent.y, 0.0);
        let length = horizontal.length();
        if !length.is_finite() || length <= 1e-12 {
            return Err(invalid(
                "station: the tangent is vertical, so it has no plan direction".into(),
            ));
        }
        let tangent = horizontal / length;
        Ok(Self {
            point: self.point,
            tangent,
            lateral: Vec3::new(-tangent.y, tangent.x, 0.0),
            up: Vec3::Z,
        })
    }

    /// The same point with its axes turned by an explicit orientation
    /// (#246): `axis` and `ref_direction` are components in THIS frame,
    /// `(tangent, lateral, up)`, defaulting to `(0, 0, 1)` and `(1, 0, 0)`.
    ///
    /// Gram-Schmidt with the axis primary: `up' = axis / |axis|`,
    /// `tangent' = normalise(r - (r . up') up')` for the unit reference
    /// direction `r`, `lateral' = up' x tangent'`. This is the reading of a
    /// linear placement's `Axis` and `RefDirection` relative to the curve
    /// (see the [module documentation](self#explicit-orientation-246)).
    ///
    /// # Errors
    ///
    /// A zero or non-finite vector, or an axis and reference direction
    /// parallel or anti-parallel within [`ORIENTATION_TOLERANCE`], by name.
    pub fn oriented(&self, axis: Option<Vec3>, ref_direction: Option<Vec3>) -> GeomResult<Self> {
        let unit = |vector: Vec3, what: &str| {
            let length = vector.length();
            if vector.is_finite() && length.is_finite() && length > 1e-12 {
                Ok(vector / length)
            } else {
                Err(invalid(format!(
                    "station: the orientation's {what} {vector:?} is zero or not finite"
                )))
            }
        };
        let axis = unit(axis.unwrap_or(Vec3::Z), "axis")?;
        let reference = unit(ref_direction.unwrap_or(Vec3::X), "reference direction")?;
        if axis.cross(reference).length() <= ORIENTATION_TOLERANCE {
            return Err(invalid(format!(
                "station: the orientation's axis {axis:?} and reference direction \
                 {reference:?} are parallel"
            )));
        }
        let x = (reference - reference.dot(axis) * axis).normalize();
        let y = axis.cross(x);
        let world = |v: Vec3| v.x * self.tangent + v.y * self.lateral + v.z * self.up;
        Ok(Self {
            point: self.point,
            tangent: world(x),
            lateral: world(y),
            up: world(axis),
        })
    }

    /// The frame in the curve-evaluation provider's layout: `x` the
    /// tangent, `y` up, `z = x x y`, which is `-lateral` (to the right).
    #[must_use]
    pub fn frame(&self) -> Frame3 {
        Frame3 {
            origin: self.point,
            x: self.tangent,
            y: self.up,
            z: -self.lateral,
        }
    }
}

/// A 2D curve's point and unit tangent lifted to `z = 0`, framed with the
/// left normal and `+Z`.
fn planar_frame(
    point: axiolid_core::Point2,
    tangent: axiolid_core::Vec2,
) -> GeomResult<SectionFrame> {
    let length = tangent.length();
    if !length.is_finite() || length <= 0.0 {
        return Err(invalid(
            "station: the curve has no tangent direction there".into(),
        ));
    }
    let t = tangent / length;
    Ok(SectionFrame {
        point: Point3::new(point.x, point.y, 0.0),
        tangent: Vec3::new(t.x, t.y, 0.0),
        lateral: Vec3::new(-t.y, t.x, 0.0),
        up: Vec3::Z,
    })
}

/// The reference-up frame against `+Z`, as `ReferenceCurveEvaluator`
/// builds it: `right = t x Z`, `up = right x t`, `lateral = -right`.
fn reference_up_frame(point: Point3, derivative: Vec3) -> GeomResult<SectionFrame> {
    let length = derivative.length();
    if !length.is_finite() || length <= 0.0 {
        return Err(invalid(
            "station: the curve has no tangent direction there".into(),
        ));
    }
    let tangent = derivative / length;
    let right = tangent.cross(Vec3::Z);
    let magnitude = right.length();
    if !magnitude.is_finite() || magnitude <= 1e-12 {
        return Err(invalid(
            "station: the tangent is vertical, so the section has no lateral axis".into(),
        ));
    }
    let right = right / magnitude;
    Ok(SectionFrame {
        point,
        tangent,
        lateral: -right,
        up: right.cross(tangent),
    })
}

/// Check `distance` against the curve length `length` (`None`:
/// unbounded) and return the distance to read, clamped onto `L` within
/// tolerance.
fn admitted(distance: Scalar, length: Option<Scalar>) -> GeomResult<Scalar> {
    if !distance.is_finite() {
        return Err(invalid(format!(
            "station: distance {distance} along the curve is not finite"
        )));
    }
    if distance < 0.0 {
        return Err(invalid(format!(
            "station: distance {distance} is before the curve's start"
        )));
    }
    match length {
        None => Ok(distance),
        Some(length) => {
            let slack = ARC_LENGTH_TOLERANCE * length.abs().max(1.0);
            if distance > length + slack {
                Err(invalid(format!(
                    "station: distance {distance} is beyond the curve's length {length}"
                )))
            } else {
                Ok(distance.min(length))
            }
        }
    }
}

fn unmeasured(dimension: &str) -> GeomError {
    invalid(format!(
        "station: this {dimension} curve family has no distance a station can be measured by"
    ))
}

/// Where a 2D curve's measure starts: parameter `0`, or the domain's
/// first parameter for a polyline or a B-spline.
fn start2(curve: &Curve2) -> Scalar {
    match curve {
        Curve2::Polyline(_) | Curve2::BSpline(_) => {
            let domain = domain2(curve);
            domain.start.min(domain.end)
        }
        _ => 0.0,
    }
}

fn start3(curve: &Curve3) -> Scalar {
    match curve {
        Curve3::Polyline(_) | Curve3::BSpline(_) => {
            let domain = domain3(curve);
            domain.start.min(domain.end)
        }
        _ => 0.0,
    }
}

/// The length a station on a 2D curve is measured against: `None` for a
/// line (unbounded), one turn for a circle or an ellipse, the arc length
/// of its domain for a polyline or a B-spline, the stated length of an
/// intrinsic curve or a chain.
///
/// # Errors
///
/// Any other family, a chain without a valid length, and the quadrature's
/// refusals, by name.
pub fn station_length2(curve: &Curve2) -> GeomResult<Option<Scalar>> {
    match curve {
        Curve2::Line(_) => Ok(None),
        Curve2::Circle(_) | Curve2::Ellipse(_) => {
            arc_length2(curve, 0.0, core::f64::consts::TAU).map(Some)
        }
        Curve2::Polyline(_) | Curve2::BSpline(_) => {
            let domain = domain2(curve);
            let (lo, hi) = (domain.start.min(domain.end), domain.start.max(domain.end));
            if hi <= lo {
                return Err(invalid("station: the curve has an empty domain".into()));
            }
            arc_length2(curve, lo, hi).map(Some)
        }
        Curve2::Intrinsic(intrinsic) => {
            if intrinsic.length.is_finite() && intrinsic.length > 0.0 {
                Ok(Some(intrinsic.length))
            } else {
                Err(invalid(
                    "station: the intrinsic curve has no positive finite length".into(),
                ))
            }
        }
        Curve2::Chain(chain) => chain
            .length()
            .map(Some)
            .ok_or_else(|| invalid("station: the chain has no valid length".into())),
        _ => Err(unmeasured("2D")),
    }
}

/// The length a station on a 3D curve is measured against, as
/// [`station_length2`]; an elevated curve's is its plan's, a banked
/// curve's the span of its cant law.
///
/// # Errors
///
/// As [`station_length2`].
pub fn station_length3(curve: &Curve3) -> GeomResult<Option<Scalar>> {
    match curve {
        Curve3::Line(_) => Ok(None),
        Curve3::Circle(_) | Curve3::Ellipse(_) => {
            arc_length3(curve, 0.0, core::f64::consts::TAU).map(Some)
        }
        Curve3::Polyline(_) | Curve3::BSpline(_) => {
            let domain = domain3(curve);
            let (lo, hi) = (domain.start.min(domain.end), domain.start.max(domain.end));
            if hi <= lo {
                return Err(invalid("station: the curve has an empty domain".into()));
            }
            arc_length3(curve, lo, hi).map(Some)
        }
        Curve3::Intrinsic(intrinsic) => {
            if intrinsic.length.is_finite() && intrinsic.length > 0.0 {
                Ok(Some(intrinsic.length))
            } else {
                Err(invalid(
                    "station: the intrinsic curve has no positive finite length".into(),
                ))
            }
        }
        Curve3::Elevated(elevated) => station_length2(&elevated.plan),
        Curve3::Banked(banked) => {
            let domain = domain3(curve);
            if domain.end > domain.start {
                Ok(Some(domain.end))
            } else {
                Err(invalid(format!(
                    "station: the banked curve's cant law has no valid span ({})",
                    banked.span()
                )))
            }
        }
        _ => Err(unmeasured("3D")),
    }
}

/// The section of a 2D curve at arc length `distance` from its start; see
/// the [module documentation](self) for the conventions.
///
/// # Errors
///
/// A distance that is not finite, negative or beyond the curve's length,
/// an unmeasurable family, and the evaluators' refusals, by name.
pub fn station_section2(curve: &Curve2, distance: Scalar) -> GeomResult<SectionFrame> {
    let distance = admitted(distance, station_length2(curve)?)?;
    let t = parameter_at_arc_length2(curve, start2(curve), distance)?;
    planar_frame(evaluate2(curve, t)?, derivative2(curve, t)?)
}

/// The section of a 3D curve at `distance` from its start: plan distance
/// on an elevated or banked curve, arc length on any other; see the
/// [module documentation](self).
///
/// # Errors
///
/// As [`station_section2`], and a vertical tangent where the reference-up
/// frame is built.
pub fn station_section3(curve: &Curve3, distance: Scalar) -> GeomResult<SectionFrame> {
    let distance = admitted(distance, station_length3(curve)?)?;
    match curve {
        Curve3::Banked(banked) => {
            let section = crate::banked::banked_section(banked, distance)?;
            Ok(SectionFrame {
                point: section.point,
                tangent: section.tangent,
                lateral: section.lateral,
                up: section.up,
            })
        }
        Curve3::Elevated(elevated) => reference_up_frame(
            crate::arc_length::elevated_point(elevated, distance)?,
            crate::arc_length::elevated_tangent(elevated, distance)?,
        ),
        _ => {
            let t = parameter_at_arc_length3(curve, start3(curve), distance)?;
            reference_up_frame(evaluate3(curve, t)?, derivative3(curve, t)?)
        }
    }
}