/usr/share/doc/rsl/users

<!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>
</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>
librsl-doc 1.43-1ubuntu1 / usr / share / doc / rsl / users_guide.html
