Creating Spectral Heat maps or Intensity maps from CDIP data using Ruby

Question

BACKGROUND

Per the Coastal Information Data Program (CDIP), they are generating a spectral heat/intensity map for wave swell at http://cdip.ucsd.edu/?nav=recent&sub=observed&units=metric&tz=UTC&pub=public&map_stati=1,2,3&stn=100&stream=p1&xitem=dir_spectrum.

This is dynamically generated with data containing energy density, duration (in seconds) & direction (in degrees with 180 degrees representing south).

DATA SAMPLE

Here's an explanation of the data: http://cdip.ucsd.edu/data_access/MEM_2dspectra.cdip

Here's a data sample for buoy 100 (same buoy as shown in the heat/intensity/spectral map: http://cdip.ucsd.edu/data_access/MEM_2dspectra.cdip?100

QUESTION

How do I take this 2-dimensional data and create a heat/intensity map ensuring that it is overlaid on Polar Coordinate map (and is the appropriate scale), just like the example url per CDIP's site?

Ultimately, I need this to be done in Ruby, preferably using ruby-gd or Rmagick, but I would greatly appreciate any language-agnostic solutions, too.

Answer 1

Chip, I know, not using Ruby, but assuming that Belisarius's point calculation is fine, I'd use Mathematica's ListContourPlot instead, as it is much simpler to understand and it gives a cleaner picture.

(* Read in data, the web address can be specified *)
a = Import[<url of cpid data>, "Table"];

Import leaves in a pre tag in the first sublist and as a single element sublist at the end, this removes it

dat = a[[ ;; -2]][[All, -72;; ]];

by first taking all but the last element, and then taking the last 72 elements of each remaining sublists.

ListContourPlot expects a list of points of the form {{x, y, f}, ...}, so we need to transform dat into that form, as explained elsewhere:

pts =Flatten[
    Table[ {
          (rr =Log[.025 + (.58 - .25)/64 r]) Cos@(tt = t 5 Degree), (* x-coord *)
          rr Sin@tt, (* y-coord *)
          dat[[r,t]] (* function value *)
           },
           {r, 7, 64}, {t, 1, 72}
         ],
    1 ]

and then plot them

ListContourPlot[pts,
  ColorFunctionScaling -> False,
  ColorFunction -> (ColorData["CMYKColors"][(# - .000007)/(.0003 - 0.000007)]&)
  ]

This gives:

which can be touched up by fixing the clipping and the ColorFunction scaling. Also, with some work radial contours could be added.

Answer 2

I am really in a rush, so can't finish right now, but as nobody answered yet, here is a first approach:

Code in Mathematica (sorry, as I said no time right now):

a = Import["http://cdip.ucsd.edu/data_access/MEM_2dspectra.cdip?100", 
   "Table"];

Graphics@Flatten[Table[

    (*colors, dont mind*)
    {ColorData["CMYKColors"][(a[[r, t]] - .000007)/(.0003 - 0.000007)], 

    (*point size, dont mind*)
    PointSize[1/Sqrt[r]/10], 

    (*Coordinates for your points "a" is your data matrix *)
       Point[
            {(rr =Log[.025 + (.58 - .25)/64 r]) Cos@(tt = t 5 Degree), 
              rr Sin@tt}]
            }

     (*values for the iteration*)
     , {r, 7, 64}, {t, 1, 72}], 1] 

     (*Rotation, dont mind*)
     /. gg : Graphics[___] :> Rotate[gg, Pi/2]  

I still can't get the right color scale: