webspice

webspice is an unofficial, experimental port of NASA's SPICE toolkit for astronomical observation geometry to WebAssembly. The aim is to enable on-line, interactive computations of advanced space observation geometry in any modern web browser without expensive server-side infrastructure or unreliable proprietary browser plugins.

The port is based on NASA's official CSPICE implementation in C, compiled to WebAssembly using Emscripten.

Installation

Use the package manager npm to install the webspice package as a local dependency under your current working directory.

npm install webspice

Usage

webspice takes the form of a JavaScript module. To use the module in your own JavaScript code, import it using the import statement:

import webspice from "./node_modules/webspice/index.js";

The location specifier must point to the location of the module in your application. Provided the browser is able to load the module from the specified location, it will bind the module's default export to the webspice identifier.

Note that the import statement may only be used from scripts that are themselves marked as type="module"; refer to the JavaScript documentation for details.

To instantiate the module, invoke the instantiate static method:

let instantiateWebspice = webspice.instantiate();

The method returns a JavaScript promise that is fulfilled once the module instance has been created. By default, the module seeks to load the WebAssembly library from the path where the module was imported from.

If the promise resolves succesfully, it will pass an instance that you can use to invoke the functions of the library:

instantiateWebspice.then(
  function (instance) {
    console.log(instance.tkvrsn_c("TOOLKIT"));
  }
);

Building

Building the webspice package from source comprise two separate parts: the CSPICE static library and the webspice library itself.

Both parts are built using Emscripten, and the path of your Emscripten toolchain must be in your shell search path for the build scripts to work. Refer to the Emscripten documentation for more information on how to accomplish this using emsdk_env.sh.

Updating CSPICE

The webspice repo comes with a copy of the official CSPICE toolkit and source code. These files can be found under upstream/import. If this copy is sufficient for you, you can skip to the next section. Should you wish to update the copy of CSPICE from the NASA/NAIF website, however, this can be accomplished by using the two scripts in the upstream directory.

To download the latest CSPICE package from NAIF into the upstream/download directory, from the upstream directory, run:

./download.sh

To import (unpack) the downloaded package into the upstream/import directory, again from the upstream directory, run:

./import.sh

Building CSPICE

The official CSPICE toolkit contains scripts for compiling the CSPICE source code to native binaries, but these scripts are not used for webspice. Instead, a select subset of the CSPICE source code is compiled to a static LLVM IR library at lib/libwebspice.a with Emscripten. To build the library, from the top-level directory, run:

./build_lib.sh

The path of your Emscripten toolchain must be in your shell search path for the build script to work.

Building webspice

To build the webspice library itself into the dist directory, from the top-level directory, run:

./build_dist.sh

The path of your Emscripten toolchain must be in your shell search path for the build script to work, and the CSPICE static library must have already been built to lib/libwebspice.a (see previous section).