This file is indexed.

/usr/share/doc/rsl/users_guide.html is in librsl-doc 1.42-2.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
<head>
   <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
   <meta name="GENERATOR" content="Mozilla/4.5 [en] (X11; U; Linux 2.0.32 i686) [Netscape]">
</head>
<body>
<a href="index.html"><img SRC="rsl.gif" height=100 width=100></a>
<hr>
<br>&nbsp;
<br>&nbsp;
<h1>
Users Guide to RSL.</h1>

<h2>
What is RSL good for?</h2>
The best feature of RSL is the ability to ingest many different RADAR data
file formats with a single library call. It can, also, read compressed
files -- compressed with GZIP or the older COMPRESS. The routine is called
<a href="RSL_anyformat_to_radar.html">RSL_anyformat_to_radar</a>.
You give it a filename and it will return a pointer to a C structure called
<a href="RSL_radar_struct.html">Radar</a>.
The structure Radar contains all the information found in the input file.
The structure is intended to represent a superset of all RADAR data formats.
<p>Below, is a table listing the input/output routines supplied in RSL.
You will notice that there are only two output routines. RSL, by design,
is not a format converter, but, a library to facilitate reading and manipulation
of RADAR data. Output for UF and HDF are supplied because of the popularity
of those two formats.
<br>&nbsp;
<table BORDER CELLPADDING=0 >
<tr>
<td>
<h4>
Data format</h4>
</td>

<td>
<h4>
Input routine</h4>
</td>

<td>
<h4>
Output routine</h4>
</td>
</tr>

<tr>
<td>HDF 1B-51 and 1C-51</td>

<td><a href="RSL_hdf_to_radar.html">RSL_hdf_to_radar</a></td>

<td><a href="RSL_radar_to_hdf.html">RSL_radar_to_hdf</a></td>
</tr>

<tr>
<td>Lassen (Darwin)</td>

<td><a href="RSL_lassen_to_radar.html">RSL_lassen_to_radar</a></td>

<td>None</td>
</tr>

<tr>
<td>WSR-88d (Nexrad)</td>

<td><a href="RSL_wsr88d_to_radar.html">RSL_wsr88d_to_radar</a></td>

<td>None</td>
</tr>

<tr>
<td>UF (Universal Format from NCAR)</td>

<td><a href="RSL_uf_to_radar.html">RSL_uf_to_radar</a></td>

<td><a href="RSL_radar_to_uf.html">RSL_radar_to_uf</a></td>
</tr>

<tr>
<td>SIGMET (Version 1)</td>

<td><a href="RSL_nsig_to_radar.html">RSL_nsig_to_radar</a></td>

<td>None</td>
</tr>

<tr>
<td>SIGMET (Version 2)</td>

<td><a href="RSL_nsig_to_radar.html">RSL_nsig2_to_radar</a></td>

<td>None</td>
</tr>

<tr>
<td>McGill&nbsp;</td>

<td><a href="RSL_mcgill_to_radar.html">RSL_mcgill_to_radar</a></td>

<td>None</td>
</tr>

<tr>
<td>TOGA&nbsp;</td>

<td><a href="RSL_toga_to_radar.html">RSL_toga_to_radar</a></td>

<td>None</td>
</tr>

<tr>
<td>RAPIC (Berrimah)&nbsp;</td>

<td><a href="RSL_rapic_to_radar.html">RSL_rapic_to_radar</a></td>

<td>None</td>
</tr>

<tr>
<td>RADTEC (SPANDAR)</td>

<td><a href="RSL_radtec_to_radar.html">RSL_radtec_to_radar</a></td>

<td>None</td>
</tr>

<tr>
<td>EDGE</td>

<td><a href="RSL_edge_to_radar.html">RSL_edge_to_radar</a></td>

<td>None</td>
</tr>
</table>
RSL is designed to provide you with a uniform data structure so that you
can design RADAR independent science applications. You no longer need to
wrestle over the input data format and have a different version of your
algorithm for each different RADAR format you may need to analyze.
<p>This paper presents RSL from a science application developer's point
of view. It will present some of the more useful routines and which fields
in the <a href="RSL_radar_struct.html">Radar</a> structure that will be
important to you and it will attempt to cover some of the programming pitfalls
associated with RSL usage. One of the most difficult hurdles to overcome
is that RSL makes extensive use of pointer syntax. You will find yourself
becoming expert with C pointers. However, the design of RSL makes it possible
to use C pointers painlessly.
<h2>
Ok, I have some data, how do I look at it?</h2>
Let's first make some images. To do that you need only 3 RSL functions:
<p><tt><a href="RSL_anyformat_to_radar.html">RSL_anyformat_to_radar</a></tt>
<br><tt><a href="RSL_load_color_table.html">RSL_load_refl_color_table</a></tt>
<br><tt><a href="RSL_volume_to.html">RSL_volume_to_gif</a></tt>
<p>The C program you need is incredibly short. It illustrates how to ingest
radar data and create a GIF image of the DZ (reflectivity) field:
<pre>#include "rsl.h"
void main(int argc, char **argv)
{
&nbsp; Radar *radar;
&nbsp; radar = RSL_anyformat_to_radar("radar.dat", NULL);
&nbsp; RSL_load_refl_color_table();
&nbsp; RSL_volume_to_gif(radar->v[DZ_INDEX], "dz_sweep", 400, 400, 200.0);
}</pre>
The line:
<p><tt>#include "rsl.h"</tt>
<p>is required when using the RSL. It defines important constants and declares
all the RSL functions that your application may need.
<p>The line:
<pre>Radar *radar;</pre>
declares the radar pointer. Only a pointer to a radar should be declared,
because, the ingest routines allocate all the space to hold all the appropriate
substructures: <a href="RSL_volume_struct.html">Volume</a>, <a href="RSL_sweep_struct.html">Sweep</a>,
<a href="RSL_ray_struct.html">Ray</a>,
and <a href="RSL_range_struct.html">Range</a>.
<p>The line:
<pre>radar = RSL_anyformat_to_radar("radar.dat", NULL);</pre>
performs the actual ingest of data. The input file is called <tt>radar.dat</tt>.
<a href="RSL_anyformat_to_radar.html">RSL_anyformat_to_radar
</a>automatically
determines the type of radar data being read. It can handle *.gz or *.Z
files transparently. Reading gzip or compress files is faster, especially
over NFS.&nbsp;&nbsp; Generally, reading compressed radar files is faster
because of how UNIX pipes are implemented and that the compression is nearly
90%.&nbsp;&nbsp; The second argument, NULL, is optional. A second argument
is needed only when reading WSR-88D data. The WSR-88D site information
is provided in the first physical file on the 8mm tape, but, it is used
to fill lat/lon and other radar-site specific information when reading
the 2<sup>nd</sup> through last physical files on the tape.
<p>Note: <a href="RSL_anyformat_to_radar.html">RSL_anyformat_to_radar</a>
can't handle every radar format for which there is an RSL ingest routine.
But, it does a good job at recognizing most formats. Currently, TOGA and
MCGILL files cannot be automatically detected. In those cases, use: <a href="RSL_toga_to_radar.html">RSL_toga_to_radar</a>
and <a href="RSL_mcgill_to_radar.html">RSL_mcgill_to_radar</a>.
<p>While basic image generation is provided in RSL, it is never intended
to be anything more than a diagnostic tool. Several assumptions are made,
but, the image generation functions provided are useful. This is what the
last two lines illustrate. First you must define a color table. That is
done with:
<pre>RSL_load_refl_color_table();</pre>
then, to generate disk files, gif images, you must call one of the image
generation functions, as in:
<pre>RSL_volume_to_gif(radar->v[DZ_INDEX], "dz_sweep", 400, 400, 200.0);</pre>
This routine will generate several images, one for each sweep, mapping
the image to a 400 x 400 km grid, using a 1 x 1 km spacing, by collecting
data out to 200 km.
<p>Making images of velocity data, <tt>VR_INDEX</tt>, involves two more
steps that are not very obvious. Because of the limited range of the values
presented in velocity data, you must re-bin the data. Do that with any
one of the following:
<pre><a href="RSL_rebin_velocity.html">RSL_rebin_velocity_sweep</a>,
<a href="RSL_rebin_velocity.html">RSL_rebin_velocity_volume</a></pre>
The second step is that you must call:
<pre><a href="RSL_load_color_table.html">RSL_load_vel_color_table()</a>;</pre>
The nyquist velocity is used to determine the limits of the re-binning.
<i>These
functions modify the data in a sweep, or volume.</i> So, it is wise to
make copies of the sweep, or volume, if you plan on using the data later
in your application. Normally, though, making velocity images is the last
step of a program, therefore, you don't need to copy the velocity volume
as your program will be exiting shortly. RSL provides a number of color
table manipulation functions. You are not limited by the default settings
for DZ, VR, and SW color tables. You can specify any color table mapping
you wish.
<h2>
Whoopty doo, I really wanted to examine the values.</h2>
In order to get to values in the <a href="RSL_radar_struct.html">Radar</a>
structure, you have to trickle down all the substructues. The structures,
in order of nesting are: <a href="RSL_radar_struct.html">Radar</a>, <a href="RSL_volume_struct.html">Volume</a>,
<a href="RSL_sweep_struct.html">Sweep</a>,
<a href="RSL_ray_struct.html">Ray</a>,
<a href="RSL_range_struct.html">Range</a>.
Each of these structures is presented in that order. You will notice a
common organization across all of the structures -- each structure contains
a header and contains an array of pointers to the next substructure.
<h4>
The Radar structure</h4>
Ok, make the call to <tt><a href="RSL_anyformat_to_radar.html">RSL_anyformat_to_radar</a></tt>
as above, so that you get a pointer to a radar. The structure <tt><a href="RSL_radar_struct.html">Radar</a></tt>
is the most general structure in RSL. Radar is composed of two parts:
<ul>
<li>
Radar header.</li>

<li>
Array of pointers to <a href="RSL_volume_struct.html">Volume</a>s.</li>
</ul>
The radar header, will be presented and described fully later, but, it
contains general information about the entire structure. To access the
radar header use the syntax:
<pre>Radar *radar;
radar->h.<i>member</i>;</pre>
The array of pointers to <a href="RSL_volume_struct.html">Volume</a>s contains
either pointers to <a href="RSL_volume_struct.html">Volume</a>s of data
or NULL. The number of possible <a href="RSL_volume_struct.html">Volume</a>s
in the radar is specified by radar->h.nvolumes. This number represents
the length of the array of pointers to <a href="RSL_volume_struct.html">Volume</a>s
and not the number of actual (non-NULL) volumes in the radar. The index
of this array of pointers to <a href="RSL_volume_struct.html">Volume</a>s
is the field type index. There are MAX_RADAR_VOLUMES (currently set to
19) field types defined in RSL. Each field type index has a specific value.
That value is illustrated in the table below. RSL ingest routines guarentee
that the length of the array of pointers to <a href="RSL_volume_struct.html">Volume</a>s,
<tt>radar->v</tt>,
is exactly the maximum number of field types, MAX_RADAR_VOLUMES. This is
done so that you can check for the existance of a field type with the syntax:
<pre>if (radar->v[XZ_INDEX]) /* XZ exists */</pre>
Normally, <tt>radar->h.nvolumes</tt> is set to the length of the array
of pointers to <a href="RSL_volume_struct.html">Volume</a>s, <tt>radar->v</tt>.
Because C array indexes start at 0, you should use a test similiar to:
ivol &lt; radar->h.nvolumes. The maximum value for <tt>radar->h.nvolumes</tt>
is MAX_RADAR_VOLUMES which is a constant in RSL. The value for <tt>radar->h.nvolumes</tt>
could be less though. But, you can rest assured that you can test for the
existance of a field type simply by using the hard coded index name as
specified in the table below.
<p>There are basically two methods for indexing the array of pointers to
<a href="RSL_volume_struct.html">Volume</a>s:
<ul>
<li>
Use the index name, eg. CZ_INDEX or its value.</li>

<li>
Use a variable that ranges from 0 to <tt>radar->h.nvolumes</tt>-1.</li>
</ul>
Here are two coding examples that demonstrate how to access the array of
pointers to volumes.
<p>Example 1:
<pre>Radar *radar;
Volume *volume;

volume = radar->v[CZ_INDEX];
if (volume != NULL) {
&nbsp;&nbsp; /* Do something with volume. */
}</pre>
Example 2:
<pre>Radar *radar;
Volume *volume;
int i;

for (i=0; i&lt;radar->h.nvolumes) {
&nbsp;&nbsp; volume = radar->v[i];
&nbsp;&nbsp; if (volume == NULL) continue; /* skip this NULL volume */
&nbsp;&nbsp; /* Do something with volume. */
}</pre>
It is very important that you check for the volume pointer being NULL.
It is very common that <tt>radar->h.nvolumes</tt> is larger than the number
of non-NULL volumes present in radar. By default, <tt>radar->h.nvolumes</tt>
is the length of array of pointers to <a href="RSL_volume_struct.html">Volume</a>s.
The volumes are also known as field types. There are several field types
and a <a href="RSL_volume_struct.html">Volume</a> can be only one field
type. The entire list of field types is presented in the table below. To
reference a particular field, you use a simple syntax:
<p><tt>radar->v[DZ_INDEX]</tt>
<br><tt>radar->v[VR_INDEX]</tt>
<p>Each field type encountered has a specific index within the <tt>radar->v</tt>
array of pointers to <a href="RSL_volume_struct.html">Volume</a>s. The
field type indexes are hard-coded and are defined to be specific numbers
starting at 0. Hard-coded field type indexes simplifies the syntax for
accessing volumes. When there is no volume for a particular field type,
the volume pointer is NULL. This is ok, as NULL is a perfectly acceptable,
albeit useless, volume. Here is a table of all the field type indexes used
in RSL.
<br>&nbsp;
<table BORDER CELLPADDING=0 >
<tr>
<td>
<h4>
INDEX NAME</h4>
</td>

<td>
<h4>
Value</h4>
</td>

<td>
<h4>
Description</h4>
</td>
</tr>

<tr>
<td>DZ_INDEX</td>

<td>0</td>

<td>Reflectivity (dBZ)</td>
</tr>

<tr>
<td>VR_INDEX</td>

<td>1</td>

<td>Radial Velocity (m/s)</td>
</tr>

<tr>
<td>SW_INDEX</td>

<td>2</td>

<td>Spectral Width (m<sup><font size=-2>2</font></sup>/s<sup><font size=-2>2</font></sup>)</td>
</tr>

<tr>
<td>CZ_INDEX</td>

<td>3</td>

<td>QC Reflectivity (dBZ)</td>
</tr>

<tr>
<td>ZT_INDEX</td>

<td>4</td>

<td>Total Reflectivity (dBZ)</td>
</tr>

<tr>
<td>DR_INDEX</td>

<td>5</td>

<td>Differential reflectivity</td>
</tr>

<tr>
<td>LR_INDEX</td>

<td>6</td>

<td>Another differential refl.</td>
</tr>

<tr>
<td>ZD_INDEX</td>

<td>7</td>

<td>Reflectivity Depolarization Ratio&nbsp;
<p>ZDR = 10log(ZH/ZV) (dB)</td>
</tr>

<tr>
<td>DM_INDEX</td>

<td>8</td>

<td>Received power (dBm)</td>
</tr>

<tr>
<td>RH_INDEX</td>

<td>9</td>

<td>Rho: Correlation coefficient</td>
</tr>

<tr>
<td>PH_INDEX</td>

<td>10</td>

<td>Phi (MCTEX parameter)</td>
</tr>

<tr>
<td>XZ_INDEX</td>

<td>11</td>

<td>X-band reflectivity</td>
</tr>

<tr>
<td>CR_INDEX</td>

<td>12</td>

<td>Corrected DR reflectivity (differential).</td>
</tr>

<tr>
<td>MZ_INDEX</td>

<td>13</td>

<td>DZ mask volume for HDF 1C-51 product.</td>
</tr>

<tr>
<td>MR_INDEX</td>

<td>14</td>

<td>DR mask volume for HDF 1C-51 product.</td>
</tr>

<tr>
<td>ZE_INDEX</td>

<td>15</td>

<td>Edited reflectivity.</td>
</tr>

<tr>
<td>VE_INDEX</td>

<td>16</td>

<td>Edited velocity.</td>
</tr>

<tr>
<td>KD_INDEX</td>

<td>17</td>

<td>KDP (unknown) for MCTEX data.</td>
</tr>

<tr>
<td>TI_INDEX</td>

<td>18</td>

<td>TIME (unknown) for MCTEX data.</td>
</tr>
</table>

<h4>
The Volume structure</h4>
The Volume structure represents the RADAR data for one, and only one, field
type. Upon ingest, the data for each field type is separated and placed
into separate volumes. This makes it convenient to manipulate volumes based
on their field type.
<p>The organization of the Volume structure closely resembles the organization
of the Radar structure. It, too, is compose of two parts:
<ul>
<li>
Volume header.</li>

<li>
Array of pointers to <a href="RSL_sweep_struct.html">Sweep</a>s.</li>
</ul>
To access elements in the Volume header, you use the syntax:
<pre>Volume *volume;
volume->h.<i>member</i>;</pre>
You can find a description of each volume header member later. The array
of pointers to <a href="RSL_sweep_struct.html">Sweep</a>s contains either
pointers to <a href="RSL_sweep_struct.html">Sweep</a>s of data or NULL.
The number of possible <a href="RSL_sweep_struct.html">Sweep</a>s in the
Volume is specified by <tt>volume->h.nsweeps</tt>. This number represents
the length of the array of pointers to <a href="RSL_sweep_struct.html">Sweep</a>s
and not the number of actual (non-NULL) sweeps in the volume.
<p>There are two methods to accessing sweeps:
<ul>
<li>
Use a loop index that ranges from 0 to <tt>volume->h.nsweeps-1</tt>.</li>

<li>
Use <a href="RSL_get_sweep.html">RSL_get_sweep</a> or other similiar RSL
sweep retieval functions.</li>
</ul>
Here are two coding examples that demonstrate how to access the array of
pointers to sweeps.
<p>Example 1:
<pre>Volume *volume;
Sweep *sweep;
int i;

/* Assume a non-NULL volume at this point. */
for (i=0; i&lt;volume->h.nsweeps; i++) {
&nbsp;&nbsp; sweep = volume->sweep[i];
&nbsp;&nbsp; if (sweep == NULL) continue; /* Skip NULL sweeps. */
&nbsp;&nbsp; /* Do something with this sweep. */
&nbsp;&nbsp; printf("Sweep %d elevation is %f\n", i, sweep->h.elev);
}</pre>
Example 2:
<pre>Volume *volume;
Sweep *sweep;
float elev;

/* No assumption about volume, it *can* be NULL! */
/* That's because RSL_get_sweep checks it. */
elev = 2.0;
sweep = RSL_get_sweep(volume, elev);
if (sweep != NULL)
&nbsp;&nbsp; printf("Sweep %d elevation is %f\n", i, sweep->h.elev);</pre>
Again, it is very important to check for NULL sweeps. By default volume->h.nsweeps
is the length of the array of pointers to <a href="RSL_sweep_struct.html">Sweep</a>s.
<h4>
The Sweep structure</h4>
The Sweep represents the data collected for one field type during one 360<sup>o</sup>
revolution of the RADAR. Like the Radar and Volume structures, the Sweep
organization is composed of two parts:
<ul>
<li>
Sweep header.</li>

<li>
Array of pointers to <a href="RSL_ray_struct.html">Ray</a>s.</li>
</ul>
To access elements in the Sweep header, you use the syntax:
<pre>Sweep *sweep;
sweep->h.<i>member</i>;</pre>
A description of each member of the Sweep header is presented later. The
array of pointers to <a href="RSL_ray_struct.html">Ray</a>s contains either
pointers to <a href="RSL_ray_struct.html">Ray</a>s of data or NULL. The
number of possible <a href="RSL_ray_struct.html">Ray</a>s in the Sweep
is specified by <tt>sweep->h.nrays</tt>. This number represents the length
of the array of pointers to <a href="RSL_ray_struct.html">Ray</a>s and
not the number of actual (non-NULL) rays in the Sweep.
<p>There are two methods to accessing rays:
<ul>
<li>
Use a loop index that ranges from 0 to <tt>sweep->h.nrays-1</tt>.</li>

<li>
Use <a href="RSL_get_ray.html">RSL_get_ray</a> or other similiar RSL ray
retieval functions.</li>
</ul>
Here are two coding examples illustrating how to access the array of pointers
to <a href="RSL_ray_struct.html">Ray</a>s.
<p>Example 1:
<pre>Sweep *sweep;
Ray *ray;
int i;

/* Assume a non-NULL sweep at this point. */
for (i=0; i&lt;sweep->h.nrays; i++) {
&nbsp;&nbsp; ray = sweep->ray[i];
&nbsp;&nbsp; if (ray == NULL) continue; /* Skip NULL rays. */
&nbsp;&nbsp; /* Do something with this ray. */
&nbsp;&nbsp; printf("Ray %d azimuth is %f\n", i, ray->h.azimuth);
}</pre>
Example 2:
<pre>Volume *volume;
Ray *ray;
float elev, azimuth;

/* No assumption about volume, it *can* be NULL! */
/* That's because RSL_get_ray checks it. */
elev = 2.0;
azimuth = 30.2;
ray = RSL_get_ray(volume, elev, azimuth);
if (ray != NULL)
&nbsp;&nbsp; printf("Ray %d elevation is %f, azimuth is %f\n", i, ray->h.elev, ray->h.azimuth);</pre>
You never know when you'll encounter NULL rays, so, make sure you test
for it. By default, sweep->h.nrays is the length of the array of pointers
to <a href="RSL_ray_struct.html">Ray</a>s which may or may not be the number
of non-NULL Rays present.
<h4>
The Ray structure</h4>
A ray of RADAR measurements represents data collected from close to the
RADAR to some maximum physical range. The <a href="RSL_ray_struct.html">Ray</a>,
too, is composed of two parts:
<ul>
<li>
Ray header.</li>

<li>
Array of field type measurements. These are not pointers. It is an array
of values.</li>
</ul>
We're getting close to the data, now. The ray header contains the largest
collection of members and describe all characteristics of the ray. To access
elements in the Ray header, you use the syntax:
<pre>Ray *ray;
ray->h.<i>member</i>;</pre>
A description of each member of the Ray header is described later. The
array of field type measurements contains the data, finally. The data type
for the data is <a href="RSL_range_struct.html">Range</a>. The <a href="RSL_range_struct.html">Range</a>
data type must be converted to float by using the function that is in ray
header: <tt>ray->h.f(r)</tt>, where <tt>r</tt> is of type <a href="RSL_range_struct.html">Range</a>.
These conversion functions are in the headers for the volume and sweep.
They are there only as a convenience to the application developer. The
number of data values in the Rays is specified by <tt>ray->h.nbins</tt>.
This number represents the length of the array of <a href="RSL_range_struct.html">Range</a>
values. There is no abiguity here, the number of data values (<a href="RSL_range_struct.html">Range</a>
values) exactly matches <tt>ray->h.nbins</tt>.
<p>There are two methods to accessing the data:
<ul>
<li>
Use a loop index that ranges from 0 to <tt>ray->h.nbins-1 </tt>calling
the <tt>ray->h.f</tt> function.</li>

<li>
Use <a href="RSL_get_value.html">RSL_get_value</a> or other similiar RSL
get value functions.</li>
</ul>
Here are two coding examples illustrating how to access the array of <a href="RSL_range_struct.html">Range</a>
values..
<p>Example 1:
<pre>Ray *ray;
int i;
float x;

/* Assume a non-NULL ray at this point. */
for (i=0; i&lt;ray->h.nbins; i++) {
&nbsp;&nbsp; x = ray->h.f(ray->range[i]);
&nbsp;&nbsp; /* Do something with this floating point value 'x'. */
&nbsp;&nbsp; printf("BIN %d value is %f\n", i, x);
}</pre>
Example 2:
<pre>Volume *volume;
float x;
float elev, azimuth, range;

/* No assumption about volume, it *can* be NULL! */
/* That's because RSL_get_value checks it. */
elev = 2.0;
azimuth = 30.2;
range = 87.3; /* KM */
x = RSL_get_value(volume, elev, azimuth, range);</pre>

<h2>
No assumptions as to the validity of the data.</h2>
The RSL does not modify the data in any way. It merely, loads the data
into the Radar structure. For instance, during the MCTEX experiment, the
azimuth values were incorrect for the first four tapes. They remain incorrect.
It is up to you to write a conversion procedure that corrects the problem.
<h2>
Pitfalls when using RSL in an application.</h2>
Here are some common mistakes made and things you should observe.
<ol>
<li>
Not checking for NULL. It is very important to check for NULL pointers.
In the RSL context, NULL is a perfectly valid ray, sweep or volume. Blindly
assuming that a volume, sweep, or ray exists is asking for trouble. When
using an RSL interface routine, a routine that is prefixed with <b>RSL_</b>,
you don't have to worry too much about passing null pointers. RSL routines
check their arguments.</li>

<li>
Not checking for NULL, when passing a volume, sweep, or ray pointer into
a routine. Check for NULL immediately.</li>

<li>
Not using the value for <tt>radar->h.nvolumes</tt>, <tt>volume->h.nsweeps</tt>,
<tt>sweep->h.nray</tt>.
They represent the maximum index possible and not the actual number of
non-NULL structures. Remember a NULL sweep, in RSL, is a valid sweep; you
just can't do anything with it. If you want to know how many non-NULL volumes
you have, you'll have to count them yourself. Do that by looping from 0
to <tt>radar->h.nvolumes - 1</tt>.</li>

<li>
Not using the value for <tt>radar->h.nvolumes</tt>, <tt>volume->h.nsweeps</tt>,
<tt>sweep->h.nrays</tt>,
and <tt>ray->h.nbins</tt> for the current object. Never assume that the
values are constant throughout the radar structure. They constantly change.
For instance, the number of bins may decrease as the sweep elevation increases.</li>

<li>
Not converting the data in the <a href="RSL_radar_struct.html">Radar</a>,
<a href="RSL_volume_struct.html">Volume</a>,
<a href="RSL_sweep_struct.html">Sweep</a>,
<a href="RSL_ray_struct.html">Ray</a>,
(really the Ray) to floating point before comparing with anything, including
comparing it with BADVAL, RFVAL, APFLAG, NOECHO. Do this conversion with
the <tt>h.f(c)</tt>, where <tt>c</tt> is <tt>ray->range[i]</tt> and is
of type <a href="RSL_range_struct.html">Range</a>. For example:</li>

<br>&nbsp;
<p>&nbsp;
<p><tt>x = ray->h.f(ray->range[ibin]);</tt>
<li>
Not converting a floating point number to internal storage with <tt>h.invf(x)</tt>,
where <tt>x</tt> is of type float, before filling the range array. For
example:</li>

<br>&nbsp;
<p>&nbsp;
<p><tt>ray->range[ibin] = ray->h.invf(x);</tt>
<li>
Forgetting to load a color table before calling an image generation function.
If you don't load a color table, your images will be black.</li>

<li>
Not rebinning the velocity data before making velocity images. The default
color table is setup to cover the range of -nyquist to +nyquist.</li>
</ol>

</body>
</html>