ericmandel / drvrem

Emscripten-based cfitsio driver to access remote FITS files without first copying them into memory

drvrem: cfitsio library with emscripten driver to access FITS files directly

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Status: works as advertised. But browsers don't allow async xhttp calls on the main thread, so the code must be run in a worker. Since this requires major changes to JS9, we will defer using this driver for now.

(In any case, its likely that this driver will be most useful for reading small sections of huge calibration files, rather than FITS data files, and JS9 does not currently need that capability.)

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The experimental cfitsio library in this repository contains drivers to allow direct access to FITS files without downloading the entire file first.

To access a FITS file directly, prepend "@" to the URL:

@https://js9.si.edu/js9/data/fits/m13.fits

NB: CORS must be respected, meaning that, in general, you can only access FITS files from the same domain as the web page.

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The v4.0.0 cfitsio library has been compiled to byte-code using emscripten, and can be used only within the emscripten environment. The byte-code files have .a extensions and are stored in the lib subdirectory. Include files have been copied to the include subdirectory.

current emcc compiler: 3.1.1

An emscripten-enabled project such as JS9 can copy the contents of the lib and include sub-directories into their own work space and then link against the byte-code libraries. For general emscripten build instructions, see the documentation at:

https://emscripten.org/docs/compiling/Building-Projects.html

For an example of the use of these particular libraries, see the Makefile in the astroem sub-directory of https://github.com/ericmandel/js9.

The libraries are compiled using the -O3 level of optimization (see the EMFLAGS variable in the top-level Makefile). Emscripten wants you to use the same optimization flags throughout the project, so if you use a different level of optimization, you probably want to change the EMFLAGS variable and rebuild the libraries by executing make all.

drvrem is distributed under the terms of The MIT License.

Eric Mandel, Center for Astrophysics | Harvard & Smithsonian