Fix Fresnel unit handling

Author: dbech

electron/raster/gdal-loader.ts

@@ -22,6 +22,16 @@ type Stats = {
   std_dev?: number;
 };
 
+type GdalUnitInfo = {
+  units?: string;
+  value?: number;
+};
+
+type SpatialReferenceWithUnits = SpatialReference & {
+  getAngularUnits?: () => GdalUnitInfo;
+  getLinearUnits?: () => GdalUnitInfo;
+};
+
 export async function loadDsmProject(
   paths: string[],
 ): Promise<DsmProjectSummary> {
@@ -76,6 +86,9 @@ export async function loadDsmProject(
       projection,
     );
     const firstNoData = openedFiles[0]!.nodata;
+    const distanceUnit = distanceUnitForSrs(firstSrs);
+    const elevationUnit = firstFile.band.unitType || "unknown";
+    const elevationMetersPerUnit = metersPerElevationUnit(elevationUnit);
 
     const summary: DsmProjectSummary = {
       id: projectId,
@@ -91,10 +104,12 @@ export async function loadDsmProject(
       ),
       crsWkt: firstSrs?.toWKT() ?? "",
       epsg,
+      distance: distanceUnit,
       extent: projectExtent,
       pixelSize: firstFile.pixelSize,
       elevation: {
-        unit: firstFile.band.unitType || "unknown",
+        unit: elevationUnit,
+        metersPerUnit: elevationMetersPerUnit,
         min: projectMin,
         max: projectMax,
         ...(firstNoData === undefined ? {} : { nodata: firstNoData }),
@@ -208,6 +223,8 @@ function warningsForProject(
   sourceSrs: SpatialReference | null,
 ): string[] {
   const warnings: string[] = [];
+  const horizontalUnit = distanceUnitForSrs(sourceSrs);
+  const elevationUnit = files[0]?.band.unitType || "unknown";
 
   if (!sourceSrs) {
     warnings.push(
@@ -219,6 +236,18 @@ function warningsForProject(
     );
   }
 
+  if (horizontalUnit.metersPerUnit === null) {
+    warnings.push(
+      "Fresnel zones are hidden because the DSM horizontal unit cannot be converted to metres.",
+    );
+  }
+
+  if (metersPerElevationUnit(elevationUnit) === null) {
+    warnings.push(
+      "Fresnel zones are hidden because the DSM elevation unit cannot be converted to metres.",
+    );
+  }
+
   for (let i = 0; i < files.length; i++) {
     for (let j = i + 1; j < files.length; j++) {
       if (extentsOverlap(files[i]!.extent, files[j]!.extent)) {
@@ -239,6 +268,57 @@ function warningsForProject(
   return warnings;
 }
 
+function distanceUnitForSrs(sourceSrs: SpatialReference | null): {
+  unit: string;
+  metersPerUnit: number | null;
+} {
+  if (!sourceSrs) return { unit: "unknown", metersPerUnit: null };
+
+  const srsWithUnits = sourceSrs as SpatialReferenceWithUnits;
+  const unitInfo = sourceSrs.isGeographic()
+    ? srsWithUnits.getAngularUnits?.()
+    : srsWithUnits.getLinearUnits?.();
+  const unit = unitInfo?.units || "unknown";
+  const metersPerUnit = sourceSrs.isGeographic()
+    ? null
+    : finitePositiveOrNull(unitInfo?.value);
+
+  return { unit, metersPerUnit };
+}
+
+function metersPerElevationUnit(unit: string): number | null {
+  const normalized = unit.trim().toLowerCase();
+  if (normalized === "" || normalized === "unknown") return null;
+
+  if (["m", "meter", "meters", "metre", "metres"].includes(normalized)) {
+    return 1;
+  }
+
+  if (
+    [
+      "ft",
+      "foot",
+      "feet",
+      "international foot",
+      "international feet",
+      "us survey foot",
+      "us survey feet",
+      "survey foot",
+      "survey feet",
+    ].includes(normalized)
+  ) {
+    return 0.3048;
+  }
+
+  return null;
+}
+
+function finitePositiveOrNull(value: number | undefined): number | null {
+  return typeof value === "number" && Number.isFinite(value) && value > 0
+    ? value
+    : null;
+}
+
 function rasterStats(band: RasterBand): Stats {
   try {
     const stats = band.computeStatistics(true) as Stats;

electron/raster/project-registry.test.ts

@@ -36,7 +36,8 @@ function testProject(id: string, close: () => void): DsmProject {
     sourceSrs: null,
     summary: {
       crsWkt: "",
-      elevation: { min: 0, max: 1, unit: "unknown" },
+      distance: { metersPerUnit: null, unit: "unknown" },
+      elevation: { metersPerUnit: null, min: 0, max: 1, unit: "unknown" },
       extent: {
         minX: 0,
         minY: 0,

src/components/path-profile-app.tsx

@@ -28,6 +28,7 @@ import { getPathProfileApi, hasDesktopBridge } from "~/lib/electron-api";
 import { exportProfileStatus } from "~/lib/export-profile-status";
 import {
   createDefaultLineOfSightEndpoints,
+  type FresnelZoneUnitScales,
   type LineOfSightEndpointId,
   type LineOfSightEndpoints,
 } from "~/lib/line-of-sight";
@@ -194,6 +195,19 @@ export function PathProfileApp() {
     project?.elevation.unit && project.elevation.unit !== "unknown"
       ? project.elevation.unit
       : null;
+  const fresnelUnitScales = useMemo<FresnelZoneUnitScales | null>(() => {
+    const horizontalMetersPerUnit = project?.distance.metersPerUnit;
+    const verticalMetersPerUnit = project?.elevation.metersPerUnit;
+
+    if (
+      !isPositiveFinite(horizontalMetersPerUnit) ||
+      !isPositiveFinite(verticalMetersPerUnit)
+    ) {
+      return null;
+    }
+
+    return { horizontalMetersPerUnit, verticalMetersPerUnit };
+  }, [project]);
 
   const noticeMessages = useMemo(
     () => (project ? warnings : ["Open a DEM from File > Open DEM..."]),
@@ -1022,6 +1036,7 @@ export function PathProfileApp() {
         <div className="min-h-0 flex-1 px-4">
           <ProfileChart
             elevationUnit={elevationUnit}
+            fresnelUnitScales={fresnelUnitScales}
             lineOfSightEndpoints={lineOfSightEndpoints}
             lineOfSightDrafts={lineOfSightDrafts}
             points={profilePoints}
@@ -1211,6 +1226,10 @@ function errorMessage(error: unknown): string {
   return error instanceof Error ? error.message : String(error);
 }
 
+function isPositiveFinite(value: number | null | undefined): value is number {
+  return typeof value === "number" && Number.isFinite(value) && value > 0;
+}
+
 function themeLabel(theme: ThemeMode): string {
   switch (theme) {
     case "system":

src/components/profile-chart.tsx

@@ -28,6 +28,7 @@ import {
   buildFresnelZoneShell,
   buildVisibleFresnelZoneShellSegments,
   buildVisibleLineOfSightSegments,
+  type FresnelZoneUnitScales,
   type LineOfSightChartPoint,
   type LineOfSightEndpointId,
   type LineOfSightEndpoints,
@@ -45,6 +46,7 @@ ChartJS.register(
 
 type ProfileChartProps = {
   elevationUnit: string | null;
+  fresnelUnitScales: FresnelZoneUnitScales | null;
   lineOfSightEndpoints: LineOfSightEndpoints | null;
   lineOfSightDrafts: LineOfSightDrafts;
   points: ProfilePoint[];
@@ -108,6 +110,7 @@ const fresnelShellDatasetOrder = 30;
  */
 export function ProfileChart({
   elevationUnit,
+  fresnelUnitScales,
   lineOfSightEndpoints,
   lineOfSightDrafts,
   points,
@@ -139,23 +142,29 @@ export function ProfileChart({
   const lastDistance = points.at(-1)?.distance ?? 0;
   const fresnelShell = useMemo(
     () =>
-      buildFresnelZoneShell(
-        points,
-        lineOfSightEndpoints,
-        fresnelFrequencyMhz,
-        FRESNEL_SHELL_NUMBER,
-      ),
-    [fresnelFrequencyMhz, lineOfSightEndpoints, points],
+      fresnelUnitScales
+        ? buildFresnelZoneShell(
+            points,
+            lineOfSightEndpoints,
+            fresnelFrequencyMhz,
+            FRESNEL_SHELL_NUMBER,
+            fresnelUnitScales,
+          )
+        : null,
+    [fresnelFrequencyMhz, fresnelUnitScales, lineOfSightEndpoints, points],
   );
   const visibleFresnelShellSegments = useMemo(
     () =>
-      buildVisibleFresnelZoneShellSegments(
-        points,
-        lineOfSightEndpoints,
-        fresnelFrequencyMhz,
-        FRESNEL_SHELL_NUMBER,
-      ),
-    [fresnelFrequencyMhz, lineOfSightEndpoints, points],
+      fresnelUnitScales
+        ? buildVisibleFresnelZoneShellSegments(
+            points,
+            lineOfSightEndpoints,
+            fresnelFrequencyMhz,
+            FRESNEL_SHELL_NUMBER,
+            fresnelUnitScales,
+          )
+        : { lower: [], upper: [] },
+    [fresnelFrequencyMhz, fresnelUnitScales, lineOfSightEndpoints, points],
   );
   const fresnelYBounds = useMemo(
     () =>
@@ -1027,7 +1036,12 @@ function distanceToSegment(
 function parseFresnelFrequencyDraft(value: string): number | null {
   if (value.trim() === "") return null;
   const frequencyMhz = Number(value);
-  return Number.isFinite(frequencyMhz) && frequencyMhz > 0
+  const frequencyHz = frequencyMhz * 1_000_000;
+
+  return Number.isFinite(frequencyMhz) &&
+    frequencyMhz > 0 &&
+    Number.isFinite(frequencyHz) &&
+    frequencyHz > 0
     ? frequencyMhz
     : null;
 }

src/lib/line-of-sight.test.ts

@@ -96,6 +96,7 @@ describe("line of sight helpers", () => {
     expect(fresnelRadiusAt(500, 1000, 0, 1)).toBeNull();
     expect(fresnelRadiusAt(500, 1000, 5800, 0)).toBeNull();
     expect(fresnelRadiusAt(1001, 1000, 5800, 1)).toBeNull();
+    expect(fresnelRadiusAt(500, 1000, Number.MIN_VALUE, 1)).toBeNull();
   });
 
   it("builds symmetric Fresnel shell lines around the line of sight", () => {
@@ -117,6 +118,19 @@ describe("line of sight helpers", () => {
     expect(shell?.lower[1]?.y).toBeCloseTo(11.41, 2);
   });
 
+  it("converts Fresnel distance and radius units for chart coordinates", () => {
+    const shell = buildFresnelZoneShell(
+      [point(0, null), point(500, null), point(1000, null)],
+      { startElevation: 10, endElevation: 20 },
+      5800,
+      1,
+      { horizontalMetersPerUnit: 0.3048, verticalMetersPerUnit: 0.3048 },
+    );
+
+    expect(shell?.upper[1]?.y).toBeCloseTo(21.51, 2);
+    expect(shell?.lower[1]?.y).toBeCloseTo(8.49, 2);
+  });
+
   it("returns null when a Fresnel shell cannot be built", () => {
     expect(
       buildFresnelZoneShell([], { startElevation: 0, endElevation: 0 }, 5800),
@@ -129,6 +143,15 @@ describe("line of sight helpers", () => {
         -1,
       ),
     ).toBeNull();
+    expect(
+      buildFresnelZoneShell(
+        [point(0, null), point(1000, null)],
+        { startElevation: 0, endElevation: 0 },
+        5800,
+        1,
+        { horizontalMetersPerUnit: 0, verticalMetersPerUnit: 1 },
+      ),
+    ).toBeNull();
   });
 
   it("builds Fresnel shell segments from visible boundary stretches", () => {
@@ -190,6 +213,15 @@ describe("line of sight helpers", () => {
         1,
       ),
     ).toEqual({ lower: [], upper: [] });
+    expect(
+      buildVisibleFresnelZoneShellSegments(
+        [point(0, 5), point(10, 5), point(20, 5)],
+        { startElevation: 10, endElevation: 10 },
+        5800,
+        1,
+        { horizontalMetersPerUnit: 1, verticalMetersPerUnit: Infinity },
+      ),
+    ).toEqual({ lower: [], upper: [] });
   });
 });