axioval_engine/

coordinate_system.rs

//! Source coordinate systems: where a source's coordinates sit.
//!
//! Every object frame and every mesh is stated in its source's own
//! coordinates. Whether two sources, or two revisions of one source, share a
//! coordinate system is a fact about the source as a whole, not about any
//! object, so this seam answers per source.
//!
//! A source may state three things, each independently:
//!
//! - its **world frame**: the frame its model coordinates are stated in,
//!   with the origin in canonical metres;
//! - **true north**: the plan direction of geographic north in those
//!   coordinates;
//! - a **map conversion**: how its coordinates map onto a named map
//!   coordinate reference system (offset, rotation, scale).
//!
//! What a source does not state is `None`, never a default: a missing map
//! conversion means the source is not georeferenced, not that it sits at the
//! map origin.

use std::sync::Arc;

use axioval_ir::{Evidence, SourceId};
use thiserror::Error;

use crate::services::reviewable_exact_evidence;
use crate::{MetricDirection, SnapshotBoundService, SourceSnapshot};

/// Failure to supply a source's coordinate system.
#[derive(Clone, Debug, Error, PartialEq, Eq)]
pub enum CoordinateSystemError {
    /// The service does not cover the source.
    #[error("coordinate-system service does not cover source `{0}`")]
    UncoveredSource(SourceId),
    /// The source states its coordinate system more than once, for example
    /// two model contexts, and nothing says which one applies.
    #[error("coordinate system is stated ambiguously: {0}")]
    Ambiguous(String),
    /// The source states it by a construct the service cannot resolve
    /// exactly.
    #[error("coordinate system unsupported: {0}")]
    Unsupported(String),
    /// A statement, or the unit it is stated in, is malformed or cannot be
    /// read exactly.
    #[error("coordinate system cannot be read exactly: {0}")]
    Unreadable(String),
    /// A value is non-finite, an axis triple is not right-handed and
    /// orthonormal, or a scale is not positive.
    #[error("coordinate system is invalid")]
    InvalidMeasurement,
    /// The evidence is not exact, not reviewable, or from another source.
    #[error("coordinate-system evidence is not exact and reviewable")]
    InexactEvidence,
    /// The service answered for another source.
    #[error("coordinate-system service answered for another source")]
    ResponseRequestMismatch,
}

/// A right-handed orthonormal frame with its origin in canonical metres.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct CoordinateFrame {
    origin_metres: [f64; 3],
    axes: [MetricDirection; 3],
}

impl CoordinateFrame {
    /// A frame; the origin must be finite and the axes a right-handed
    /// orthonormal triple.
    pub fn try_new(
        origin_metres: [f64; 3],
        x: MetricDirection,
        y: MetricDirection,
        z: MetricDirection,
    ) -> Result<Self, CoordinateSystemError> {
        const ORTHOGONAL_TOLERANCE: f64 = 1.0e-9;
        if !origin_metres.iter().all(|value| value.is_finite()) {
            return Err(CoordinateSystemError::InvalidMeasurement);
        }
        let dot = |a: [f64; 3], b: [f64; 3]| a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
        let [first, second, third] = [x.components(), y.components(), z.components()];
        let cross = [
            first[1] * second[2] - first[2] * second[1],
            first[2] * second[0] - first[0] * second[2],
            first[0] * second[1] - first[1] * second[0],
        ];
        if dot(first, second).abs() > ORTHOGONAL_TOLERANCE
            || dot(first, third).abs() > ORTHOGONAL_TOLERANCE
            || dot(second, third).abs() > ORTHOGONAL_TOLERANCE
            || dot(cross, third) < 1.0 - ORTHOGONAL_TOLERANCE
        {
            return Err(CoordinateSystemError::InvalidMeasurement);
        }
        Ok(Self {
            origin_metres,
            axes: [x, y, z],
        })
    }

    /// The origin, in canonical metres.
    #[must_use]
    pub fn origin_metres(&self) -> [f64; 3] {
        self.origin_metres
    }

    /// The X, Y and Z axes.
    #[must_use]
    pub fn axes(&self) -> [MetricDirection; 3] {
        self.axes
    }
}

/// How a source's coordinates map onto a map coordinate reference system.
#[derive(Clone, Debug, PartialEq)]
pub struct MapConversion {
    target: Option<String>,
    offset: [f64; 3],
    x_axis: [f64; 2],
    scale: f64,
    metres_per_map_unit: Option<f64>,
}

impl MapConversion {
    /// A map conversion.
    ///
    /// `offset` is easting, northing and orthogonal height in the map's unit;
    /// `x_axis` is the direction of the source's X axis in the map's plan
    /// (abscissa, ordinate) and is normalized; `scale` is the factor from
    /// source to map lengths. `metres_per_map_unit` is `None` when the map's
    /// unit is not stated or cannot be resolved exactly, never a guess.
    pub fn try_new(
        target: Option<String>,
        offset: [f64; 3],
        x_axis: [f64; 2],
        scale: f64,
        metres_per_map_unit: Option<f64>,
    ) -> Result<Self, CoordinateSystemError> {
        let norm = x_axis[0].hypot(x_axis[1]);
        let valid = offset.iter().all(|value| value.is_finite())
            && norm.is_finite()
            && norm > f64::EPSILON
            && scale.is_finite()
            && scale > 0.0
            && metres_per_map_unit.is_none_or(|unit| unit.is_finite() && unit > 0.0)
            && target.as_deref().is_none_or(|name| !name.trim().is_empty());
        if !valid {
            return Err(CoordinateSystemError::InvalidMeasurement);
        }
        Ok(Self {
            target,
            offset,
            x_axis: [x_axis[0] / norm, x_axis[1] / norm],
            scale,
            metres_per_map_unit,
        })
    }

    /// The name of the target map coordinate reference system, when stated.
    #[must_use]
    pub fn target(&self) -> Option<&str> {
        self.target.as_deref()
    }

    /// Easting, northing and orthogonal height, in the map's unit.
    #[must_use]
    pub fn offset(&self) -> [f64; 3] {
        self.offset
    }

    /// Unit direction of the source's X axis in the map's plan.
    #[must_use]
    pub fn x_axis(&self) -> [f64; 2] {
        self.x_axis
    }

    /// Scale from source lengths to map lengths.
    #[must_use]
    pub fn scale(&self) -> f64 {
        self.scale
    }

    /// Metres per map unit, or `None` when the unit is not known exactly.
    #[must_use]
    pub fn metres_per_map_unit(&self) -> Option<f64> {
        self.metres_per_map_unit
    }

    /// The offset in metres, when the map's unit is known.
    #[must_use]
    pub fn offset_metres(&self) -> Option<[f64; 3]> {
        self.metres_per_map_unit
            .map(|unit| self.offset.map(|value| value * unit))
    }
}

/// One source's coordinate system, as far as the source states it.
#[derive(Clone, Debug, PartialEq)]
pub struct SourceCoordinateSystem {
    source: SourceId,
    world: Option<CoordinateFrame>,
    true_north: Option<[f64; 2]>,
    map: Option<MapConversion>,
    evidence: Evidence,
}

impl SourceCoordinateSystem {
    /// The coordinate system of `source`.
    ///
    /// `true_north` is a plan direction and is normalized. The evidence must
    /// be exact, reviewable and from `source`: a coordinate system is stated,
    /// never estimated.
    pub fn try_new(
        source: SourceId,
        world: Option<CoordinateFrame>,
        true_north: Option<[f64; 2]>,
        map: Option<MapConversion>,
        evidence: Evidence,
    ) -> Result<Self, CoordinateSystemError> {
        let true_north = match true_north {
            Some([x, y]) => {
                let norm = x.hypot(y);
                if !norm.is_finite() || norm <= f64::EPSILON {
                    return Err(CoordinateSystemError::InvalidMeasurement);
                }
                Some([x / norm, y / norm])
            }
            None => None,
        };
        if !reviewable_exact_evidence(&evidence) || evidence.source != source {
            return Err(CoordinateSystemError::InexactEvidence);
        }
        Ok(Self {
            source,
            world,
            true_north,
            map,
            evidence,
        })
    }

    /// The source this coordinate system belongs to.
    #[must_use]
    pub fn source(&self) -> &SourceId {
        &self.source
    }

    /// The frame the source's coordinates are stated in, when stated.
    #[must_use]
    pub fn world(&self) -> Option<&CoordinateFrame> {
        self.world.as_ref()
    }

    /// Unit plan direction of true north, when stated.
    #[must_use]
    pub fn true_north(&self) -> Option<[f64; 2]> {
        self.true_north
    }

    /// The map conversion, when the source is georeferenced.
    #[must_use]
    pub fn map(&self) -> Option<&MapConversion> {
        self.map.as_ref()
    }

    /// Reviewable provenance of the statements.
    #[must_use]
    pub fn evidence(&self) -> &Evidence {
        &self.evidence
    }
}

/// Trusted adapter seam supplying sources' coordinate systems.
pub trait CoordinateSystemService: Send + Sync + 'static {
    /// Exact source snapshots this service answers for.
    fn source_snapshots(&self) -> &[SourceSnapshot];
    /// The coordinate system of `source`, or why it cannot be read.
    fn coordinate_system(
        &self,
        source: &SourceId,
    ) -> Result<SourceCoordinateSystem, CoordinateSystemError>;
}

/// Registry handle for a [`CoordinateSystemService`].
#[derive(Clone)]
pub struct CoordinateSystemServiceHandle(Arc<dyn CoordinateSystemService>);

impl CoordinateSystemServiceHandle {
    /// Wraps a trusted coordinate-system service.
    #[must_use]
    pub fn new(service: Arc<dyn CoordinateSystemService>) -> Self {
        Self(service)
    }

    /// The coordinate system of `source`. An uncovered source is refused,
    /// and so is an answer about another source.
    pub fn coordinate_system(
        &self,
        source: &SourceId,
    ) -> Result<SourceCoordinateSystem, CoordinateSystemError> {
        if !self
            .0
            .source_snapshots()
            .iter()
            .any(|snapshot| snapshot.source() == source)
        {
            return Err(CoordinateSystemError::UncoveredSource(source.clone()));
        }
        let answer = self.0.coordinate_system(source)?;
        if answer.source() != source {
            return Err(CoordinateSystemError::ResponseRequestMismatch);
        }
        Ok(answer)
    }
}

impl SnapshotBoundService for CoordinateSystemServiceHandle {
    fn source_snapshots(&self) -> &[SourceSnapshot] {
        self.0.source_snapshots()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn source(name: &str) -> SourceId {
        SourceId::new("cad", name).unwrap()
    }

    fn direction(vector: [f64; 3]) -> MetricDirection {
        MetricDirection::try_new(vector).unwrap()
    }

    fn identity() -> [MetricDirection; 3] {
        [
            direction([1.0, 0.0, 0.0]),
            direction([0.0, 1.0, 0.0]),
            direction([0.0, 0.0, 1.0]),
        ]
    }

    #[test]
    fn a_frame_must_be_right_handed_and_finite() {
        let [x, y, z] = identity();
        assert!(CoordinateFrame::try_new([0.0; 3], x, y, z).is_ok());
        assert_eq!(
            CoordinateFrame::try_new([0.0; 3], direction([-1.0, 0.0, 0.0]), y, z),
            Err(CoordinateSystemError::InvalidMeasurement)
        );
        assert_eq!(
            CoordinateFrame::try_new([f64::NAN, 0.0, 0.0], x, y, z),
            Err(CoordinateSystemError::InvalidMeasurement)
        );
    }

    #[test]
    #[allow(clippy::float_cmp)] // Normalizing an axis-aligned vector is exact.
    fn a_map_conversion_needs_a_positive_scale_and_a_direction() {
        assert!(MapConversion::try_new(None, [1.0, 2.0, 3.0], [1.0, 0.0], 1.0, None).is_ok());
        for (axis, scale, unit) in [
            ([0.0, 0.0], 1.0, None),
            ([1.0, 0.0], 0.0, None),
            ([1.0, 0.0], 1.0, Some(-1.0)),
        ] {
            assert_eq!(
                MapConversion::try_new(None, [0.0; 3], axis, scale, unit),
                Err(CoordinateSystemError::InvalidMeasurement)
            );
        }
        let map =
            MapConversion::try_new(None, [1.0, 2.0, 3.0], [0.0, 2.0], 1.0, Some(0.001)).unwrap();
        assert_eq!(map.x_axis(), [0.0, 1.0]);
        assert_eq!(map.offset_metres(), Some([0.001, 0.002, 0.003]));
    }

    #[test]
    fn evidence_must_be_exact_and_from_the_source() {
        let foreign = Evidence::exact(source("b"), "crs");
        assert_eq!(
            SourceCoordinateSystem::try_new(source("a"), None, None, None, foreign),
            Err(CoordinateSystemError::InexactEvidence)
        );
        let system = SourceCoordinateSystem::try_new(
            source("a"),
            None,
            Some([0.0, 3.0]),
            None,
            Evidence::exact(source("a"), "crs"),
        )
        .unwrap();
        assert_eq!(system.true_north(), Some([0.0, 1.0]));
    }

    struct Fixed(Vec<SourceSnapshot>, SourceCoordinateSystem);
    impl CoordinateSystemService for Fixed {
        fn source_snapshots(&self) -> &[SourceSnapshot] {
            &self.0
        }
        fn coordinate_system(
            &self,
            _: &SourceId,
        ) -> Result<SourceCoordinateSystem, CoordinateSystemError> {
            Ok(self.1.clone())
        }
    }

    #[test]
    fn the_handle_binds_answers_to_the_request() {
        let snapshots = vec![
            SourceSnapshot::try_new(source("a"), "r", "sha256:a").unwrap(),
            SourceSnapshot::try_new(source("b"), "r", "sha256:b").unwrap(),
        ];
        let answer = SourceCoordinateSystem::try_new(
            source("a"),
            None,
            None,
            None,
            Evidence::exact(source("a"), "crs"),
        )
        .unwrap();
        let handle = CoordinateSystemServiceHandle::new(Arc::new(Fixed(snapshots, answer)));
        assert!(handle.coordinate_system(&source("a")).is_ok());
        assert_eq!(
            handle.coordinate_system(&source("b")),
            Err(CoordinateSystemError::ResponseRequestMismatch)
        );
        assert_eq!(
            handle.coordinate_system(&source("c")),
            Err(CoordinateSystemError::UncoveredSource(source("c")))
        );
    }
}