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[Datastream #SLC-598796]: data format for nldn lightning data
- Subject: [Datastream #SLC-598796]: data format for nldn lightning data
- Date: Tue, 05 Jun 2007 07:39:31 -0600
Hi Gerry,
re:
> Please send me the input format (c-struct or code would be fine) for the
> nldn lightning data. We have a number of archived raw data files that I
> need to decode.
The NLDN data is contained in a binary record whose values are as follows:
header mixed; variable length
time_sec int
time_nsec int
latitude int
longitude int
fill value short
signal short
fill value short
multiplicity char
fill value char
semimajor char
eccentricity char
angle char
chisquare char
In order to better understand the structure of the NLDN record, I am
attaching a routine I use to read the data.
> Thanks,
No worries.
Cheers,
Tom
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Ticket Details
===================
Ticket ID: SLC-598796
Department: Support Datastream
Priority: Normal
Status: Closed/* ---------------------------------------------------------------------
**
** Name: ingestnldn.c
**
** Purpose: Read NLDN binary records from LDM feed
**
** History: 940302 - Adapted from 'ingesttonc.c' written by Ron
** Henderson of SUNY Albany
**
** ---------------------------------------------------------------------
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <assert.h>
#include <signal.h>
#include "ulog.h"
#include "cfortran.h"
#include "alarm.h"
static unsigned alarm_timeout = 60; /* seconds; should suffice */
#define INGESTORFLASHLEN 28
/*
* SIGALRM handler.
*/
static void
alarm_handler(sig)
int sig;
{
assert(SIGALRM == sig);
uerror("nldninput(): no data for %u seconds: simulating EOF",
alarm_timeout);
}
/*
* Read a character from a file.
*
* Returns:
* 1 Success
* 0 Failure
*/
static int
read_char(file, value)
FILE *file;
char *value;
{
return fread(value, 1, 1, file) == 1;
}
/*
* Read a short from a file.
*
* Returns:
* 1 Success
* 0 Failure
*/
static int
read_short(file, value)
FILE *file;
short *value;
{
unsigned char x[2]; /* NB: 16-bits assumed! */
int retcode;
int num = 1;
if (fread(x, 1, sizeof(x), file) == sizeof(x))
{
*value = (x[0] << 8) | x[1];
retcode = 1;
}
else
{
retcode = 0;
}
return retcode;
}
/*
* Read an integer from a file.
*
* Returns:
* 1 Success
* 0 Failure
*/
static int
read_int(file, value)
FILE *file;
int *value;
{
unsigned char x[4]; /* NB: 32-bits assumed! */
int retcode;
int num = 1;
if (fread(x, 1, sizeof(x), file) == sizeof(x))
{
*value = (x[0] << 24) | (x[1] << 16) | (x[2] << 8) | x[3];
retcode = 1;
}
else
{
retcode = 0;
}
return retcode;
}
/*
* Read an undetermined 4-byte sequence from a file; determine whether
* or not it is a beginning of a header record; eat all header records
* if they exist; and return the integer value at the beginning of a
* flash record.
*
* Returns:
* 1 Success
* 0 Failure
*/
static int
read_begin(file, value)
FILE *file;
int *value;
{
unsigned char x[4]; /* NB: 32-bits assumed! */
int retcode = 0; /* failure default */
int num = 1;
if (fread(x, 1, sizeof(x), file) == sizeof(x))
{
if (strncmp((const char *)x, "NLDN", 4) != 0)
{
/*
* Not a header record. Just return the data value.
*/
retcode = 1;
}
else
{
/*
* Start of header records. Read them and the first data
* value.
*/
int nhead;
uinfo("nldninput(): Product header record found");
if (read_int(file, &nhead))
{
int nflash;
if (read_int(file, &nflash))
{
unsigned char headr[280]; /* NB: 32-bits assumed! */
int bufsiz = nhead * INGESTORFLASHLEN - 12;
if (fread(&headr[12], 1, bufsiz, file) == bufsiz)
{
if (nflash != 0)
{
if (fread(x, 1, sizeof(x), file) == sizeof(x))
retcode = 1;
}
}
}
}
}
if (retcode == 1)
*value = (x[0] << 24) | (x[1] << 16) | (x[2] << 8) | x[3];
}
return retcode;
}
/*
* Read an NLDN record from a file stream.
*
* Returns:
* 1 Success
* 0 Failure
*/
static int
nldn_read(file, time_sec, time_nsec, lat, lon, sgnl, mult, semimaj, eccent,
angle, chisqr)
FILE *file;
int *time_sec;
int *time_nsec;
float *lat;
float *lon;
float *sgnl;
int *mult;
float *semimaj;
float *eccent;
float *angle;
float *chisqr;
{
int iret;
int nbytes;
short fill_short;
char fill_char;
struct
{
int lat;
int lon;
short sgnl;
char mult;
char semimaj;
char eccent;
char angle;
char chisqr;
} obs;
int retcode = 0; /* failure */
if ( read_begin(file, time_sec) && /* 32-bits assumed */
read_int(file, time_nsec) && /* 32-bits assumed */
read_int(file, &obs.lat) &&
read_int(file, &obs.lon) &&
read_short(file, &fill_short) &&
read_short(file, &obs.sgnl) &&
read_short(file, &fill_short) &&
read_char(file, &obs.mult) &&
read_char(file, &fill_char) &&
read_char(file, &obs.semimaj) &&
read_char(file, &obs.eccent) &&
read_char(file, &obs.angle) &&
read_char(file, &obs.chisqr) )
{
*lat = obs.lat / 1000.0;
*lon = obs.lon / 1000.0;
*sgnl = obs.sgnl / 10.0;
*mult = obs.mult;
*semimaj = obs.semimaj;
*eccent = obs.eccent;
*angle = obs.angle;
*chisqr = obs.chisqr;
retcode = 1;
}
return retcode;
}
/*
* Return parameters from the input. In order to handle the situation in
* which we're being fed by an LDM and the end of the data product is never
* seen, we set an alarm prior to the read.
*
* Returns:
* -1 Error: read error or EOF
* 0 No data
* INGESTORFLASHLEN Number of bytes read
*/
int
nldninput(time_sec, time_nsec, lat, lon, sgnl, mult, semimaj, eccent,
angle, chisqr)
int *time_sec;
int *time_nsec;
float *lat;
float *lon;
float *sgnl;
int *mult;
float *semimaj;
float *eccent;
float *angle;
float *chisqr;
{
int retcode = -1; /* failure default */
int ok;
static int alarm_initialized = 0;
static Alarm timeout_alarm;
if (!alarm_initialized)
{
alarm_init(&timeout_alarm, alarm_timeout, alarm_handler);
alarm_initialized = 1;
}
alarm_on(&timeout_alarm); /* set alarm */
ok = nldn_read(stdin, time_sec, time_nsec, lat, lon, sgnl, mult,
semimaj, eccent, angle, chisqr);
alarm_off(&timeout_alarm); /* disable alarm */
if (ok)
retcode = INGESTORFLASHLEN;
else
{
if (feof(stdin))
{
uinfo("nldninput(): EOF on stdin");
}
else if (ferror(stdin))
{
serror("nldninput(): NLDN read error");
}
else
{
uinfo("nldninput(): No data to read");
retcode = 0;
}
}
return retcode;
}
/*
* FORTRAN interface to the above function.
*/
FCALLSCFUN10(INT,nldninput,NLDNIN,nldnin,PINT,PINT,PFLOAT,PFLOAT,PFLOAT,PINT,PFLOAT,PFLOAT,PFLOAT,PFLOAT)