Thomas, Just wanted to say that I find this very interesting. As an astronomer, I have lots of .fits data from HST observations. I've not worked with them for a while -- when I did I used IDL routines written by Space Telescope staff. If I were to go back to them now, I probably would use python, and especially the tools in the "astropy" distrubition. But it is neat to have a native tool in J. I've just tried your code & it does display the test images (though one of my old Hubble images fails). So when I get a bit of time I'll try to understand what you have done. Anyway, I just wanted to let you know that there is interest in this project!
Patrick On Thu, 19 Apr 2018, Thomas Hickey wrote:
This is, of course, great. Thank you and I'll try to incorporate most of it. I noticed that the links in my gmail copy of this post worked, but those with trailing periods in the archive don't because the link there somehow incorporates the period. --Th On Wed, Apr 18, 2018 at 6:16 PM, Marshall Lochbaum <[email protected]> wrote:This is a perfectly good use of the forums in my book. At the very least, we've had similar posts before and no one's complained. Overall your program looks pretty good to me. It's not leveraging the Full Power of J™, but it's a great start. You know what I. does! There are some ways to use arrays to do more of your work for you. You write 'minCut maxCut' =. x ... minWanted =: (<.minCut*#srtData){srtData maxWanted =: (<.maxCut*#srtData){srtData but this is the same as 'minWanted maxWanted' =: (<.x*#srtData){srtData since each of * <. and { has rank zero, that is, maps over arrays, on the side of x. (Unrelatedly, these should probably use =. rather than =: to avoid global assignment. It looks like they might have been =: for debugging, but if so, it's good practice to look over the code again and change them back when you're done.) A more sophisticated example is the plane-scaling code in displayFits. You use different code for each different number of scalings to do: r =. minmax scaleT2D 0{imarray select. 3<.{.$imarray NB. use up to 3 planes case. 3 do. g =. minmax scaleT2D 1{imarray b =. minmax scaleT2D 2{imarray case. 2 do. b =. minmax scaleT2D 1{imarray g =. -: r+b NB. average of red and blue case. 1 do. 'g b'=. r;r end. Instead, you could do all the scalings in one go: ((#imarray) is like ({.$imarray), but it is a scalar and not a vector.) numScales =. 3<.#imarray NB. use up to 3 planes scaled =. minmax scaleT2D"_ _1 numScales {. imarray if. numScales < 3 do. avg =. (+/ % #) scaled scaled =. scaled , (3-numScales)#,:avg end. 'r g b' =. scaled This example first uses scaleT2D with an explicit rank to operate on each of the first numScales planes. If you're not familiar with it, my favorite explanation of the rank conjunction (") is http://www.jsoftware.com/help/jforc/loopless_code_i_verbs_have_r.htm. A rank of (_ _1), that is, infinity on the left and minus one on the right, means to apply the function to the entire left argument and each subarray of the right argument, effectively mapping over only the right argument. I could have used a rank of 2 rather than _1 on the right, but rank _1 is more flexible--it would work even if the planes were instead three-dimensional. After this compuation, scaled is a three-dimensional array of the first numScales planes of imarray. The average of its planes can be found with the standard averaging function (+/ % #), which happens to be the canonical example of a fork. If you're interested, these are described at http://code.jsoftware.com/wiki/Vocabulary/fork. An exponent like (2^8) unfortunately always evaluates to a floating-point number. I habitually use (<.@^) when I know the arguments are integers to avoid accidentally promoting to floats. I actually gave a talk on a task similar to the parsing you do here. My task was to parse the header of a simple wave file. A script version (there's no recording that I'm aware of) is at http://code.jsoftware.com/wiki/Community/Conference2014/ Talks/UsingDataAsCode and the current script that I use based on this is https://github.com/mlochbaum/JSound/blob/master/wav.ijs. This is certainly difficult material for a beginning J programmer, but the techniques discussed in the talk might be useful for you as you gain more skill. One neat trick similar to the one used there: rather than write bitpix =. hdata getHdrVal 'BITPIX' naxis =. hdata getHdrVal 'NAXIS' naxis1 =. hdata getHdrVal 'NAXIS1' naxis2 =. hdata getHdrVal 'NAXIS2' naxis3 =. hdata getHdrVal 'NAXIS3' you might use fields =. ;: 'BITPIX NAXIS NAXIS1 NAXIS2 NAXIS3' (fields) =. hdata&getHdrVal&.> fields and then the fields will be defined in variables BITPIX, etc. Another very cool trick that I found after the talk would be useful here: select. bitpix case. _32 do. adata =. (naxis3,naxis2,naxis1)$ |. _1 fc |. rdata case. _64 do. adata =. (naxis3,naxis2,naxis1)$ |. _2 fc |. rdata case. 16 do. adata =. (naxis3,naxis2,naxis1)$ |. _1 ic |. rdata case. 32 do. adata =. (naxis3,naxis2,naxis1)$ |. _2 ic |. rdata end. The idea is to make an adverb (mine is audioconvert in wav.ijs) which takes a format specification like bitpix and returns a conversion function. Something like: rawconvert =: 1 : 0 select. u case. _32 do. _1&fc case. _64 do. _2&fc case. 16 do. _1&ic case. 32 do. _2&ic case. do. 'Invalid format' assert 0 end. ) which can then be called with cvt =. bitpix rawconvert NB. A conversion function adata =. (naxis3,naxis2,naxis1)$ |. cvt |. rdata Now the really cool thing is that J knows how to invert each of these functions. So when you want to store the data again, you just use (cvt^:_1)! This is a J-only technique: I don't know of any other language that has the functional capabilities and the automatic inversion required to do it. There's always more to say but I think that's enough for one email. Good luck with your future J projects! Marshall On Wed, Apr 18, 2018 at 02:47:02PM -0400, Thomas Hickey wrote: > As one of my first J programs, I've written a minimal viewer for FITS > files, the standard way of sharing astronomical data, especially images. > > I'd appreciate it if someone could take a look at it and let me know how > the code (80 lines of J) looks. I know I've replaced some really awkward > code in it, so I imagine there are better ways of doing lots of things. > > The code is on GitHub at https://github.com/ThomasBHickey/JFits, along > with a sample FITS file in the fitsSample folder. Pointers on organizing J > code on GitHub would be appreciated as well. > > Or is there a better way to accomplish this than the programming forum? I > know this is longer than most of the questions that are posted here, but I > think it is an interesting application of J. > > --Th > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
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