City-Lifeline-Cockpit/tools/city-massing/terrain-height-frame.mjs

// Original DEM ellipsoid heights must be converted before use as ENU mesh Z.
import assert from 'node:assert/strict'
import { Cartesian3, Matrix4 } from 'cesium'

export function terrainInLocalFrame(transform, samples, heights) {
    assert.equal(samples.length, heights.length, 'terrain point/height mismatch')
    const inverse = Matrix4.inverseTransformation(Matrix4.fromArray(transform), new Matrix4())
    return samples.map((sample, index) => {
        assert.ok(Number.isFinite(heights[index]) && heights[index] > 1, 'invalid original DEM height')
        const local = Matrix4.multiplyByPoint(inverse,
            Cartesian3.fromDegrees(sample.lon, sample.lat, heights[index]), new Cartesian3())
        return [local.x, local.y, local.z]
    })
}

export function localSeatingLevels(transform, samples, heights) {
    const points = terrainInLocalFrame(transform, samples, heights)
    const minimum = Math.min(...points.map(p => p[2])), maximum = Math.max(...points.map(p => p[2]))
    return { minimum, maximum, relief: maximum - minimum,
        floorZ: maximum - .25, foundationBottom: minimum - 3,
        ellipsoidMinimum: Math.min(...heights), ellipsoidMaximum: Math.max(...heights),
        heightFrame: 'project-local-ENU-up' }
}