== Help File ==

This subroutine, nomads_data_probe, is designed to get data for a single point 
for the latest data from a given model available on the nomads server.  

Parameters are passed to the subroutine in an array.

example:
$info['model_name'] = 'nam';					// (1) name of the model
$info['model_subset'] = 'nam_';                                 // (2) subset or variation of the model
$info['longitude'] = -122.59499999                              // (3) longitude of the point 
$info['latitude']  = 45.58916666;				// (4) latitude of the point
$info['constraint'] = 'tmp2m[0:28][300:301][267:268]';          // (5) the 'constraint' or filter to use in the request.




(1) Model Name
    A directory of the models available on the NOMADS server is available at
    https://nomads.ncep.noaa.gov/dods/

    This subroutine may not work on some models

(2) Model Subset
    "Subset" is probably a bad word here, but it refers to the various directories for a particular
    model in the day/date directory for that model.  Drill down from https://nomads.ncep.noaa.gov/dods/
    to see what's available.

(3) (4)  Longitude and Latitude.
	 Negative latitude values south of the equator, negative longitude values west of the prime maredian.
         
         It's up to the  user to ensure the point requested is within the domain of the chosen model.
    
         See below for more information on how data is interpolated from the four surrounding grid points
         to the location requested. 


(5) NOMADS DODS Constraint Info:

   You're going to have to experiment to get the 'constraint' expression right.  The good
   news is you can test various expessions directly from a browser.

   Here's a NOMADS ascii query:
                 1                 2      3         4      5      6     7    8    9    10
   |------------------------------| |--||----------||-----||----| |----||----||---||---||---| 
   http://nomads.ncep.noaa.gov/dods/nam/nam20231104/nam_00z.ascii?tmpprs[0:19][0:1][1:1][1:1]  


   1. This is the base URL - shouldn't change

   2. Model name.  You can get this from: https://nomads.ncep.noaa.gov/dods/

   3. Model name as above and dtg in the form YYYYMMDD

   4. Model subset and valid time. Easiest way to get this is to drill down from 
   https://nomads.ncep.noaa.gov/dods/ but you can get them using a url
   consisting of elements 1, 2 and 3.

   5. 'ascii' is a key word which directs the server to send the data as ascii text

   6. This is the name of the parameter(s)requested.  Separate parameters with 
   a comma.  The list of parameters available is on the .info page for the 
   model subset.  Again, the easiest way to get this is to drill down from 
   https://nomads.ncep.noaa.gov/dods/ but you can get them using a url 
   consisting of elements 1, 2, 3, and 4 with '.info' appended.

   7. Beginning and ending time steps.  Number of timesteps can be found in 
   the '.info' file.

   8. Level identifier.  This can be tricky.  You need to figure out the number 
   of the level in which you're interested.  Check the '.info' page

   9. Latitude range.  Latitude is expressed in grid points and can be tricky to 
   convert from degrees latitude.

   10. Longitude range. Longitude is expressed in grid points and can be tricky to
   convert from degrees longitude. 

  To use nomads_data_probe_v3 you'll need to build the 'constraint' or filtering 
  instructions.  This is everything after the question mark in the ascii query url.

  Agaom can experiment with this by directly querying the NOMADS server directly from 
  a browser.


Longitude/latitude Interpolation Scheme

  Routine gets the data values at the four grid points surrounding the location
  requested. Does a linear East-West interpolation between NW and NE as well as 
  SW and SE.  It then does a linear interpolation between those intermediate points.

                               |<-e/w%->| 
                           NW  .        .                  . NE
 
 
 

                               .        . <-- lat/lon      .     ---
                                              (point of          /\
                                               interest           |
                                                                 n/s%
                                                                  |
                                                                 \/
                            SW  .        .                  . SE ---