30:[{"id":"f5c0bb7fbc561141274cd09f59c61068eebf9224ddc24a866cb33116afb236f3e194b417f70db7e14f2257d5b0ab29eac5a2c6cc3633ee35585c12a07eb6152f","href":"https://static.observableusercontent.com/files/f5c0bb7fbc561141274cd09f59c61068eebf9224ddc24a866cb33116afb236f3e194b417f70db7e14f2257d5b0ab29eac5a2c6cc3633ee35585c12a07eb6152f","name":"wasm_exec (1).js","type":"application/javascript","lastModified":1661547092635.186,"size":16612},{"id":"894685becfdc64ab34dcdd9b423a46e087719aa6278e5171e3ef31e5f05e382df6a566d27643fb6f1cc6d03ceae908268c47d618931c0a786d6682fc7d4631a0","href":"https://static.observableusercontent.com/files/894685becfdc64ab34dcdd9b423a46e087719aa6278e5171e3ef31e5f05e382df6a566d27643fb6f1cc6d03ceae908268c47d618931c0a786d6682fc7d4631a0","name":"ab020010.22o","type":"application/octet-stream","lastModified":1661787950043.519,"size":5576913},{"id":"b628d223e2de08337a29553123c41db5679ed919b8ca5bf0b7aa053de066f0add5f70f8b649b7dfcbd8151758d31f1b4ea9196b5b988e8a064af18646e703c1c","href":"https://static.observableusercontent.com/files/b628d223e2de08337a29553123c41db5679ed919b8ca5bf0b7aa053de066f0add5f70f8b649b7dfcbd8151758d31f1b4ea9196b5b988e8a064af18646e703c1c","name":"main (3).wasm","type":"application/wasm","lastModified":1661785578652.328,"size":2750824},{"id":"ae035788c83648ed0249752eb6c767481accee3625b9edfa49cc1dfe62488a405333934c1cafdd42b920a023c009362020ba0b9a9b07b6241264c1ff471f7080","href":"https://static.observableusercontent.com/files/ae035788c83648ed0249752eb6c767481accee3625b9edfa49cc1dfe62488a405333934c1cafdd42b920a023c009362020ba0b9a9b07b6241264c1ff471f7080","name":"igs_rinex.jpeg","type":"image/jpeg","lastModified":1661789430489.142,"size":109342}] 2e:{"title":"RINEX to JSON","cells":[{"id":0,"value":"# RINEX to JSON","pinned":false,"hidden":false,"mode":"md"},{"id":464,"value":"

\n \n

Using Go and Web Assembly in the Observable environment, we show how to parse a RINEX file to create JSON that allows for immedate inspection and data visualization in the browser.

\n","pinned":false,"hidden":false,"mode":"html"},{"id":316,"value":"Upload an *uncompressed* RINEX file (e.g. `\\ab010010.22o`\\ is the default file).","pinned":false,"hidden":false,"mode":"md"},{"id":7,"value":"viewof file = fileuploader({\n description:\n \"Drag and drop RINEX observation file (e.g. ab020010.22o is default)\",\n default: FileAttachment(\"ab020010.22o\")\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":408,"value":"Here are the **${d3.format(\",\")(table.length)}** RINEX observations from the uploaded file. Click on the little menu left of the cell below to download the table as **CSV** or **JSON** file.","pinned":false,"hidden":false,"mode":"md"},{"id":399,"value":"viewof table = Inputs.table(data, {\n columns: [\n \"time\",\n \"system\",\n \"sv\",\n \"code\",\n // \"freq\",\n // \"fcn\",\n \"range\",\n \"phase\",\n // \"doppler\",\n \"snr\",\n \"lli\"\n // \"flags\"\n ],\n format: {\n system: (d) => system[d], // Map number code to name of GPS constellation,\n lli: (d) => 1 & d // loss of lock, bitwise mask\n }\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":633,"value":"### The following steps break down how the table above was produced.","pinned":false,"hidden":false,"mode":"md"},{"id":319,"value":"**1.** Your uploaded file is first converted into a Byte Array.","pinned":false,"hidden":false,"mode":"md"},{"id":616,"value":"File size: **${bytesToString(byteArray.length)}**","pinned":false,"hidden":false,"mode":"md"},{"id":14,"value":"byteArray = file.arrayBuffer().then((d) => new Uint8Array(d))","pinned":true,"hidden":false,"mode":"ojs"},{"id":321,"value":"**2.** A function written in [Go](https://go.dev/) is compiled to Web Assembly so it can run in the browser. *See the Appendix for more on the Web Assembly part.* We call that function with the byte array from (1) and get an *array* of Byte Arrays in return.","pinned":false,"hidden":false,"mode":"md"},{"id":595,"value":"benchmark\n ? md`Compute time: **${d3.format(\".2f\")(benchmark / 1e3)} seconds**`\n : md``","pinned":false,"hidden":false,"mode":"ojs"},{"id":274,"value":"wasmBytes = {\n wasm;\n let t0 = Date.now();\n let result = window.rinex2Json(byteArray);\n mutable benchmark = Date.now() - t0;\n return result;\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":326,"value":"**3.** We loop over our array of Byte Arrays and turn each byte array into a string that happens to represent a JSON structure. Now we have an array of *strings*.","pinned":false,"hidden":false,"mode":"md"},{"id":299,"value":"text = {\n return wasmBytes.map((d) => String.fromCharCode(...d));\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":330,"value":"**4.** Looping over our array of strings, we *parse* each string as a JSON object. Now we have an array of data structures that we can easily interact with in this Observable notebook.","pinned":false,"hidden":false,"mode":"md"},{"id":305,"value":"json = text.map((d) => JSON.parse(d))","pinned":true,"hidden":false,"mode":"ojs"},{"id":370,"value":"**5.** Now merge our the *parsed* arrays together to produce on array with timestamped observations that can easily be rendered as plots.","pinned":false,"hidden":false,"mode":"md"},{"id":343,"value":"data = d3.merge(\n json.map((d) => {\n d.obs.forEach((t) => (t.time = d3.timeParse(\"%Y-%m-%dT%H:%M:%SZ\")(d.time)));\n return d.obs;\n })\n)","pinned":true,"hidden":false,"mode":"ojs"},{"id":391,"value":"**6. **Here's a plot of the Signal to Noise Radio (SNR) for the observation file you uploaded. A randomly distributed subset of observations from the uploaded file are rendered.","pinned":false,"hidden":false,"mode":"md"},{"id":571,"value":"viewof p = Inputs.range([1, 25], {\n step: 1,\n value: 5,\n label: \"Sample %\"\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":446,"value":"viewof k = Inputs.range([1, 360], {\n step: 1,\n value: 240,\n label: \"Moving Average (samples)\"\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":438,"value":"sample = data.filter((d) => Math.random() > 1 - p / 100)","pinned":false,"hidden":false,"mode":"ojs"},{"id":378,"value":"snr_plot = Plot.plot({\n width: width,\n y: {\n grid: true\n },\n marks: [\n Plot.dot(sample, { x: \"time\", y: \"snr\", fill: \"black\", opacity: 0.5 }),\n Plot.line(\n sample,\n Plot.windowY({ k: k, x: \"time\", y: \"snr\", stroke: \"red\" })\n )\n ]\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":674,"value":"The chart below shows loss of lock for each numbered satellite.","pinned":false,"hidden":false,"mode":"md"},{"id":649,"value":"lli_plot = Plot.plot({\n width: width,\n y: {\n grid: true\n },\n marks: [\n Plot.dot(sample, {\n x: \"time\",\n y: (d) => d.sv,\n fill: (d) => (1 & d.lli ? \"red\" : \"#ccc\"),\n opacity: 0.8,\n r: 2\n })\n ]\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":85,"value":"---\n## Appendix\n\nA Web Assembly Module compiled from Go is loaded in the browser by asychronously loading and evaluating a wasm_exec.js file produced by the Go compiler along with a wasm file containing useful Go functions that we intend to use from Javascript. In the simplest case, we have a .js helper file and a wasm file that must be loaded one after the other before we can interact with the webassembly code in the browser. That happens below:\n\n### WASM 🪄 ","pinned":false,"hidden":false,"mode":"md"},{"id":45,"value":"// Load wasm_exec.js produced by the golang compiler.\nloadWasmExec = async (callback) => {\n const text = await FileAttachment(\"wasm_exec (1).js\").text();\n\n const script = document.createElement(\"script\");\n const code = document.createTextNode(text);\n script.appendChild(code);\n script.onload = callback;\n\n // The script will modify variables on window.\n document.body.appendChild(script);\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":70,"value":"// Load the wasm file and run the main function.\ninstantiateWasm = async () => {\n const { Go } = window;\n const go = new Go();\n\n const headers = new Headers();\n headers.set(\"Content-Type\", \"application/wasm\");\n const response = new Response(\n await FileAttachment(\"main (3).wasm\").arrayBuffer(),\n {\n headers: headers\n }\n );\n\n return WebAssembly.instantiateStreaming(response, go.importObject).then(\n (result) => {\n go.run(result.instance);\n console.log(result.instance.exports);\n return result.instance;\n }\n );\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":63,"value":"// One file must be loaded before the other to setup the wasm environment.\nwasm = {\n await loadWasmExec(() => {});\n return await instantiateWasm(() => {});\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":591,"value":"mutable benchmark = undefined","pinned":false,"hidden":false,"mode":"ojs"},{"id":489,"value":"### Miscellaneous","pinned":false,"hidden":false,"mode":"md"},{"id":619,"value":"// e.g. 10394879 -> 10MB\nbytesToString = function (bytes) {\n let format = d3.format(\".0f\");\n\n if (bytes < 1024) {\n return format(bytes) + \"B\";\n } else if (bytes < 1024 * 1024) {\n return format(bytes / 1024) + \"kB\";\n } else if (bytes < 1024 * 1024 * 1024) {\n return format(bytes / 1024 / 1024) + \"MB\";\n } else if (bytes < 1024 * 1024 * 1024 * 1024) {\n return format(bytes / 1024 / 1024 / 1024) + \"GB\";\n } else if (bytes < 1024 * 1024 * 1024 * 1024 * 1024) {\n return format(bytes / 1024 / 1024 / 1024 / 1024) + \"TB\";\n } else {\n return (\n d3.format(\",\")(format(bytes / 1024 / 1024 / 1024 / 1024 / 1024)) + \"PB\"\n );\n }\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":492,"value":"system = ({\n 0: \"GPS\",\n 1: \"GLO\",\n 2: \"SBAS\",\n 3: \"GAL\",\n 4: \"BDS\",\n 5: \"QZSS\",\n 6: \"IRNSS\"\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":471,"value":"import { fileuploader } from \"@fil/fileuploader\"","pinned":false,"hidden":false,"mode":"ojs"}],"files":"$W30","stdlib":"1","titling":"auto"}