feat(examples): add geom-terrain-viz demo

thi-ng · Oct 20, 2023 · c55d6eb · c55d6eb
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diff --git a/assets/examples/geom-terrain-viz.jpg b/assets/examples/geom-terrain-viz.jpg
diff --git a/examples/geom-terrain-viz/README.md b/examples/geom-terrain-viz/README.md
@@ -0,0 +1,15 @@
+# geom-terrain-viz
+
+![screenshot](https://raw.githubusercontent.com/thi-ng/umbrella/develop/assets/examples/geom-terrain-viz.jpg)
+
+[Live demo](http://demo.thi.ng/umbrella/geom-terrain-viz/)
+
+Please refer to the [example build instructions](https://github.com/thi-ng/umbrella/wiki/Example-build-instructions) on the wiki.
+
+## Authors
+
+- Karsten Schmidt
+
+## License
+
+&copy; 2023 Karsten Schmidt // Apache Software License 2.0
diff --git a/examples/geom-terrain-viz/index.html b/examples/geom-terrain-viz/index.html
@@ -0,0 +1,29 @@
+<!DOCTYPE html>
+<html lang="en">
+	<head>
+		<link
+			rel="icon"
+			href='data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100"><text y=".9em" font-size="90">⛱️</text></svg>'
+		/>
+		<meta http-equiv="Content-Type" content="text/html;charset=UTF-8" />
+		<meta name="viewport" content="width=device-width, initial-scale=1.0" />
+		<meta http-equiv="X-UA-Compatible" content="ie=edge" />
+		<title>geom-terrain-viz · @thi.ng/umbrella</title>
+		<link
+			href="https://unpkg.com/tachyons@4/css/tachyons.min.css"
+			rel="stylesheet"
+		/>
+		<style></style>
+	</head>
+	<body class="sans-serif">
+		<div id="app"></div>
+		<div>
+			<a
+				class="link"
+				href="https://github.com/thi-ng/umbrella/tree/develop/examples/geom-terrain-viz"
+				>Source code</a
+			>
+		</div>
+		<script type="module" src="/src/index.ts"></script>
+	</body>
+</html>
diff --git a/examples/geom-terrain-viz/package.json b/examples/geom-terrain-viz/package.json
@@ -0,0 +1,41 @@
+{
+	"name": "@example/geom-terrain-viz",
+	"version": "0.0.1",
+	"private": true,
+	"description": "2.5D hidden line visualization of digital elevation files (DEM)",
+	"repository": "https://github.com/thi-ng/umbrella",
+	"author": "Karsten Schmidt <[email protected]>",
+	"license": "Apache-2.0",
+	"scripts": {
+		"start": "vite --open",
+		"build": "tsc && vite build --base='./'",
+		"preview": "vite preview --host --open"
+	},
+	"devDependencies": {
+		"typescript": "^5.2.2",
+		"vite": "^4.4.9"
+	},
+	"dependencies": {
+		"@thi.ng/api": "workspace:^",
+		"@thi.ng/dl-asset": "workspace:^",
+		"@thi.ng/geom": "workspace:^",
+		"@thi.ng/math": "workspace:^",
+		"@thi.ng/pixel": "workspace:^",
+		"@thi.ng/rdom-canvas": "workspace:^",
+		"@thi.ng/rstream": "workspace:^",
+		"@thi.ng/transducers": "workspace:^",
+		"@thi.ng/vectors": "workspace:^"
+	},
+	"browser": {
+		"process": false
+	},
+	"thi.ng": {
+		"readme": [
+			"dl-asset",
+			"geom",
+			"pixel",
+			"rdom-canvas"
+		],
+		"screenshot": "examples/geom-terrain-viz.jpg"
+	}
+}
diff --git a/examples/geom-terrain-viz/src/index.ts b/examples/geom-terrain-viz/src/index.ts
@@ -0,0 +1,177 @@
+import type { Nullable } from "@thi.ng/api";
+import { download, downloadCanvas } from "@thi.ng/dl-asset";
+import { asSvg, group, polyline, svgDoc } from "@thi.ng/geom";
+import { fit } from "@thi.ng/math";
+import {
+	FLOAT_GRAY,
+	GAUSSIAN,
+	convolveImage,
+	defSampler,
+	floatBufferFromImage,
+	imagePromise,
+	type FloatSampler,
+} from "@thi.ng/pixel";
+import { $canvas } from "@thi.ng/rdom-canvas";
+import { fromIterable, reactive } from "@thi.ng/rstream";
+import { map, range } from "@thi.ng/transducers";
+import { madd2, type ReadonlyVec } from "@thi.ng/vectors";
+
+// Image sourced from USGS (https://earthexplorer.usgs.gov/)
+import IMG from "./n46_w123_1arc_v3-crop2.jpg";
+
+// canvas size
+const WIDTH = 1280;
+const HEIGHT = 720;
+// elevation scale
+const ELEVATION = 250;
+// Y tilt/stretch
+const YTILT = ELEVATION / 4;
+// sample every N pixel cols/rows (fractional step sizes supported!)
+const XSTEP = 1;
+const YSTEP = 1;
+// flip view flag (flip coordinates, for DEMs this means view from north)
+const FLIP = true;
+// gaussian blur radius
+const BLUR = 2;
+// terrain color
+const STROKE = "#557";
+
+// function to sample a pixel row from the image and transform into a polyline.
+// the pixel values are read via given sampler (which we'll later configure to
+// use bicubic interpolation) and therefore can use fractional positions (in
+// both X & Y directions)
+const polylineFromPixels = (
+	sampler: FloatSampler,
+	width: number,
+	y: number,
+	screenPos: ReadonlyVec,
+	screenScale: ReadonlyVec,
+	stepX = 1
+) =>
+	polyline(
+		map(
+			(x) =>
+				// sample image to obtain Y position, then scale & translate to
+				// configure screenspace
+				madd2(
+					null,
+					[x, sampler(x, y)[0] - 0.5],
+					screenScale,
+					screenPos
+				),
+			range(0, width, stepX)
+		)
+	);
+
+// function to clip/segment given polyline vertices against an existing horizon
+// line we will use screenspace coordinates (with -Y as the up axis). the
+// polyline will be split into segments whenever it crosses the horizon and only
+// segments above the horizon are kept. the function also computes & returns the
+// new horizon for future (re)use.
+const hiddenPolyline = (pts: ReadonlyVec[], horizon: ReadonlyVec[]) => {
+	const res: ReadonlyVec[][] = [];
+	const newHorizon: ReadonlyVec[] = [];
+	let newSeg = true;
+	for (let i = 0, n = pts.length; i < n; i++) {
+		const p = pts[i];
+		const h = horizon[i];
+		// check if P is above horizon (-Y up)
+		if (p[1] <= h[1]) {
+			if (newSeg) {
+				res.push(i > 0 ? [horizon[i - 1]] : []);
+				newSeg = false;
+			}
+			res[res.length - 1].push(p);
+			// update horizon using P's position
+			newHorizon.push(p);
+		} else {
+			// P is below horizon...
+			// if still an active above-horizon segment, close it
+			if (!newSeg) {
+				res[res.length - 1].push(h);
+				newSeg = true;
+			}
+			// keep current horizon position
+			newHorizon.push(h);
+		}
+	}
+	return { segments: res, newHorizon };
+};
+
+// main function is only async to simplify image loading via promises
+(async () => {
+	// create an empty group to store geometry (the bg color attrib is only used
+	// for canvas drawing)
+	const scene = group({ __background: "#fdc" });
+	// create a reactive wrapper for the scene
+	const geo = reactive(scene);
+	// create a reactive canvas to subscribe to `geo` and handle automatic re-drawing
+	const canvas = <HTMLCanvasElement>(
+		await $canvas(geo, [WIDTH, HEIGHT]).mount(
+			document.getElementById("app")!
+		)
+	);
+	// load image, convert to grayscale floating point image buffer
+	let img = floatBufferFromImage(await imagePromise(IMG), FLOAT_GRAY);
+	// optionally blur the image with a bit of gaussian blur to reduce noise/jitter
+	// see https://thi.ng/pixel readme for alternatives
+	img = convolveImage(img, { kernel: GAUSSIAN(BLUR) });
+	// create a bicubic image sampler (to allow sampling at fractional positions)
+	const sampler = defSampler(img, "cubic", "repeat");
+	// precompute scaling vector from image space to screen space
+	const SCALE = [(WIDTH / img.width) * (FLIP ? -1 : 1), -ELEVATION];
+	// variable to hold the evolving horizon line (vertices only)
+	let horizon: Nullable<ReadonlyVec[]>;
+	// create a timesliced stream of Y positions to sample the image we also add
+	// a subscription to process this stream of values, each time processing a
+	// single pixel row and adding the resulting geometry to the scene (and
+	// updating the canvas)
+	fromIterable(range(1, img.height, YSTEP), { delay: 16 }).subscribe({
+		// subscription handler which is called for each new value
+		next(y) {
+			// compute Y position in screen space
+			const screenY = fit(y, img.height, 0, -YTILT, HEIGHT + YTILT);
+			// sample pixel row and create polyline
+			// (taking FLIP config into account to adjust params)
+			const line = polylineFromPixels(
+				sampler,
+				img.width,
+				FLIP ? y : img.height - y,
+				[FLIP ? WIDTH : 0, screenY],
+				SCALE,
+				XSTEP
+			);
+			// if we've got already a horizon (i.e. not 1st frame),
+			// clip the new line and update the horizon...
+			if (horizon) {
+				const { segments, newHorizon } = hiddenPolyline(
+					line.points,
+					horizon
+				);
+				horizon = newHorizon;
+				// create polylines for each resulting segment and wrap into a
+				// group node
+				const row = group(
+					{ stroke: STROKE },
+					segments.map((pts) => polyline(pts))
+				);
+				// add to main group
+				scene.add(row);
+				// send to canvas (which is subscribed to the `geo` stream)
+				geo.next(row);
+			} else {
+				// in first frame merely record the sampled points as initial horizon
+				horizon = line.points;
+			}
+		},
+		// subscription handler which is called when the stream is exhausted/done
+		// (i.e. in this case when the range() iterator is finished)
+		done() {
+			const baseName = `terrain-${Date.now()}`;
+			// convert geometry to SVG & download
+			download(baseName + `.svg`, asSvg(svgDoc({}, scene)));
+			// also download canvas (by default as PNG)
+			downloadCanvas(canvas, baseName);
+		},
+	});
+})();
diff --git a/examples/geom-terrain-viz/src/n46_w123_1arc_v3-crop2.jpg b/examples/geom-terrain-viz/src/n46_w123_1arc_v3-crop2.jpg
diff --git a/examples/geom-terrain-viz/src/vite-env.d.ts b/examples/geom-terrain-viz/src/vite-env.d.ts
@@ -0,0 +1 @@
+/// <reference types="vite/client" />
diff --git a/examples/geom-terrain-viz/tsconfig.json b/examples/geom-terrain-viz/tsconfig.json
@@ -0,0 +1,6 @@
+{
+	"extends": "../tsconfig.json",
+	"include": ["src/**/*"],
+	"compilerOptions": {
+	}
+}
diff --git a/yarn.lock b/yarn.lock
@@ -715,6 +715,24 @@ __metadata:
   languageName: unknown
   linkType: soft
 
+"@example/geom-terrain-viz@workspace:examples/geom-terrain-viz":
+  version: 0.0.0-use.local
+  resolution: "@example/geom-terrain-viz@workspace:examples/geom-terrain-viz"
+  dependencies:
+    "@thi.ng/api": "workspace:^"
+    "@thi.ng/dl-asset": "workspace:^"
+    "@thi.ng/geom": "workspace:^"
+    "@thi.ng/math": "workspace:^"
+    "@thi.ng/pixel": "workspace:^"
+    "@thi.ng/rdom-canvas": "workspace:^"
+    "@thi.ng/rstream": "workspace:^"
+    "@thi.ng/transducers": "workspace:^"
+    "@thi.ng/vectors": "workspace:^"
+    typescript: ^5.2.2
+    vite: ^4.4.9
+  languageName: unknown
+  linkType: soft
+
 "@example/geom-tessel@workspace:examples/geom-tessel":
   version: 0.0.0-use.local
   resolution: "@example/geom-tessel@workspace:examples/geom-tessel"