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ephem0.cpp
5647 lines (5122 loc) · 217 KB
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ephem0.cpp
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/* ephem0.cpp: low-level funcs for ephemerides & pseudo-MPECs
Copyright (C) 2010, Project Pluto
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA. */
#if defined( _WIN32) || defined( __WATCOMC__)
#include <direct.h> /* for _mkdir() definition */
#else
#include <sys/stat.h>
#include <sys/types.h>
#endif
#ifdef __linux
#include <linux/limits.h>
#endif
#include <sys/types.h>
#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
#include <ctype.h>
#include <assert.h>
#include <stdbool.h>
#include "watdefs.h"
#include "afuncs.h"
#include "lunar.h"
#include "date.h"
#include "comets.h"
#include "mpc_func.h"
#include "mpc_obs.h"
#include "vislimit.h"
#include "brentmin.h"
#include "stackall.h"
#include "expcalc.h"
#include "rgb_defs.h"
#include "stringex.h"
#include "constant.h"
#define LOG_10 2.3025850929940456840179914546843642076011014886287729760333279009675726
#define LIGHT_YEAR_IN_KM (365.25 * seconds_per_day * SPEED_OF_LIGHT)
int generic_message_box( const char *message, const char *box_type);
double centralize_ang( double ang); /* elem_out.cpp */
double vector_to_polar( double *lon, double *lat, const double *vector);
char *fgets_trimmed( char *buff, size_t max_bytes, FILE *ifile); /*elem_out.c*/
int parallax_to_lat_alt( const double rho_cos_phi, const double rho_sin_phi,
double *lat, double *ht_in_meters, const int planet_idx); /* ephem0.c */
double calc_obs_magnitude( const double obj_sun,
const double obj_earth, const double earth_sun, double *phase_ang);
int lat_alt_to_parallax( const double lat, const double ht_in_meters,
double *rho_cos_phi, double *rho_sin_phi, const int planet_idx);
int write_residuals_to_file( const char *filename, const char *ast_filename,
const int n_obs, const OBSERVE FAR *obs_data, const int format);
void light_time_lag( const double jde, const double *orbit, /* orb_func.c */
const double *observer, double *result, const int is_heliocentric);
void put_observer_data_in_text( const char FAR *mpc_code, char *buff);
int make_pseudo_mpec( const char *mpec_filename, const char *obj_name);
/* ephem0.cpp */
int earth_lunar_posn( const double jd, double FAR *earth_loc,
double FAR *lunar_loc);
bool nighttime_only( const char *mpc_code); /* mpc_obs.cpp */
double get_planet_mass( const int planet_idx); /* orb_func.c */
void remove_trailing_cr_lf( char *buff); /* ephem0.cpp */
const char *get_environment_ptr( const char *env_ptr); /* mpc_obs.cpp */
void set_environment_ptr( const char *env_ptr, const char *new_value);
uint64_t parse_bit_string( const char *istr); /* miscell.cpp */
void format_dist_in_buff( char *buff, const double dist_in_au); /* ephem0.c */
int debug_printf( const char *format, ...) /* mpc_obs.cpp */
#ifdef __GNUC__
__attribute__ (( format( printf, 1, 2)))
#endif
;
int calc_derivatives( const double jd, const double *ival, double *oval,
const int reference_planet); /* runge.cpp */
char *iso_time( char *buff, const double jd, const int precision); /* elem_out.c */
double mag_band_shift( const char mag_band, int *err_code); /* elem_out.c */
char *get_file_name( char *filename, const char *template_file_name);
double utc_from_td( const double jdt, double *delta_t); /* ephem0.cpp */
double diameter_from_abs_mag( const double abs_mag, /* ephem0.cpp */
const double optical_albedo);
double shadow_check( const double *planet_loc, /* ephem0.cpp */
const double *obs_posn,
const double planet_radius_in_au);
int get_object_name( char *obuff, const char *packed_desig); /* mpc_obs.c */
int get_residual_data( const OBSERVE *obs, double *xresid, double *yresid);
int setup_planet_elem( ELEMENTS *elem, const int planet_idx,
const double t_cen); /* moid4.c */
void calc_approx_planet_orientation( const int planet, /* runge.cpp */
const int system_number, const double jde, double *matrix);
char *mpc_station_name( char *station_data); /* mpc_obs.cpp */
FILE *fopen_ext( const char *filename, const char *permits); /* miscell.cpp */
int remove_rgb_code( char *buff); /* ephem0.cpp */
static void put_residual_into_text( char *text, const double resid,
const int resid_format); /* ephem0.cpp */
FILE *open_json_file( char *filename, const char *env_ptr, const char *default_name,
const char *packed_desig, const char *permits); /* ephem0.cpp */
void shellsort_r( void *base, const size_t n_elements, const size_t elem_size,
int (*compare)(const void *, const void *, void *), void *context);
const char *default_observe_filename = "observe.txt";
const char *observe_filename = default_observe_filename;
const char *residual_filename = "residual.txt";
const char *ephemeris_filename = "ephemeri.txt";
bool is_default_ephem = true;
const char *elements_filename = "elements.txt";
static expcalc_config_t exposure_config;
extern int n_orbit_params;
/* Returns parallax constants (rho_cos_phi, rho_sin_phi) in AU. */
int lat_alt_to_parallax( const double lat, const double ht_in_meters,
double *rho_cos_phi, double *rho_sin_phi, const int planet_idx)
{
const double axis_ratio = planet_axis_ratio( planet_idx);
const double major_axis_in_meters = planet_radius_in_meters( planet_idx);
const double u = atan( sin( lat) * axis_ratio / cos( lat));
*rho_sin_phi = axis_ratio * sin( u) +
(ht_in_meters / major_axis_in_meters) * sin( lat);
*rho_cos_phi = cos( u) + (ht_in_meters / major_axis_in_meters) * cos( lat);
*rho_sin_phi *= major_axis_in_meters / AU_IN_METERS;
*rho_cos_phi *= major_axis_in_meters / AU_IN_METERS;
return( 0);
}
/* Parallax constants (rho_cos_phi, rho_sin_phi) should be in units of the
planet's equatorial radius. */
int parallax_to_lat_alt( const double rho_cos_phi, const double rho_sin_phi,
double *lat, double *ht_in_meters, const int planet_idx)
{
double talt = 0.;
const double tlat = point_to_ellipse( 1., planet_axis_ratio( planet_idx),
rho_cos_phi, rho_sin_phi, &talt);
if( lat)
*lat = tlat;
if( ht_in_meters)
*ht_in_meters = talt * planet_radius_in_meters( planet_idx);
return( 0);
}
/* format_dist_in_buff() formats the input distance (in AU) into a
seven-byte buffer. It does this by choosing suitable units: kilometers
if the distance is less than a million km, AU out to 10000 AU, then
light-years. In actual use, light-years indicates some sort of error,
but I wanted the program to handle that problem without just crashing.
28 Dec 2009: To help puzzle out a strange bug, I extended things so
that distances beyond 10000 light-years could be shown in kilo-light-years
(KLY), mega, giga, etc. units, making up prefixes after 'yocto'. Thus,
one "ALY" = 10^78 light-years. Since the universe is 13.7 billion years
old, and nothing can be seen beyond that point, such distances are
physically unreasonable by a factor of roughly 10^68. But for debugging
purposes, display of these distances was useful. The bug is now fixed,
so with any luck, nobody should see such distances again.
2012 Feb 13: there's some interest in determining orbits of _very_
close objects, such as tennis balls. To address this, short distances
are now shown in millimeters, centimeters, meters, or .1 km,
as appropriate.
NOTE: It used to be that I followed MPC practice in showing all distances
between .01 and ten AU in the form d.dddd , but now, that's only true for
one to ten AU. For distances less than 1 AU, I'm using .ddddd, thereby
getting an extra digit displayed. */
static void show_dist_in_au( char *buff, const double dist_in_au)
{
const char *fmt;
if( dist_in_au > 999.999)
fmt = "%7.1f"; /* " 1234.5" */
else if( dist_in_au > 99.999)
fmt = "%7.2f"; /* " 123.45" */
else if( dist_in_au > 9.999)
fmt = "%7.3f"; /* " 12.345" */
else if( dist_in_au > .99) /* used to be .01 */
fmt = "%7.4f"; /* " 1.2345" */
else
fmt = "%7.5f"; /* " .12345" */
snprintf( buff, 8, fmt, dist_in_au);
*buff = ' '; /* remove leading zero for small amounts */
}
static const char *si_prefixes = "kMGTPEZYRQXWVUSONLJIHFDCBA";
static bool use_au_only = false;
/* Given a non-negative value, this gives a four-character output
such as '3.14', '.314', '3145', '314k', '3.1M', etc. */
static void show_packed_with_si_prefixes( char *buff, double ival)
{
*buff = '\0';
if( ival > 999.e+21)
strcpy( buff, "!!!!");
else if( ival > 9999.)
{
unsigned count = 0;
*buff = '\0';
while( !*buff)
{
ival /= 1000.;
if( ival < 9.9)
snprintf( buff, 5, "%3.1f%c", ival, si_prefixes[count]);
else if( ival < 999.)
snprintf( buff, 5, "%3u%c", (unsigned)ival, si_prefixes[count]);
count++;
}
}
else if( ival > 99.9)
snprintf( buff, 5, "%4u", (unsigned)( ival + .5));
else if( ival > 9.99)
snprintf( buff, 5, "%4.1f", ival);
else if( ival > .99)
snprintf( buff, 5, "%4.2f", ival);
else
{
char tbuff[7];
snprintf( tbuff, sizeof( tbuff), "%5.2f", ival);
strcpy( buff, tbuff + 1); /* store value without leading 0 */
}
}
void format_dist_in_buff( char *buff, const double dist_in_au)
{
if( dist_in_au < 0.)
strcpy( buff, " <NEG!>");
else if( use_au_only == true)
show_dist_in_au( buff, dist_in_au);
else
{
const double dist_in_km = dist_in_au * AU_IN_KM;
const char *fmt;
/* for objects within a million km (about 2.5 times */
/* the distance to the moon), switch to km/m/cm/mm: */
if( dist_in_km < .0099) /* 0 to 9900 millimeters: */
snprintf( buff, 8, "%5.0fmm", dist_in_km * 1e+6); /* " NNNNmm" */
else if( dist_in_km < .099) /* 990 to 9900 centimeters: */
snprintf( buff, 8, "%5.0fcm", dist_in_km * 1e+5); /* " NNNNcm" */
else if( dist_in_km < 99.) /* 99 to 99000 meters: */
snprintf( buff, 8, "%6.0fm", dist_in_km * 1e+3); /* " NNNNNm" */
else if( dist_in_km < 999.) /* 99.0 to 999.9 kilometers: */
snprintf( buff, 8, "%6.1fk", dist_in_km); /* " NNN.Nk" */
else if( dist_in_km < 999999.) /* 999.9 to 999999 km: */
snprintf( buff, 8, "%7.0f", dist_in_km);
else if( dist_in_au > 9999.999)
{
double dist_in_light_years =
dist_in_au * AU_IN_KM / LIGHT_YEAR_IN_KM;
if( dist_in_light_years > 9999.9)
{
int idx = 0;
dist_in_light_years /= 1000;
for( idx = 0; si_prefixes[idx] && dist_in_light_years > 999.; idx++)
dist_in_light_years /= 1000;
if( !si_prefixes[idx]) /* can't represent this even in our */
strcpy( buff, " <HUGE>"); /* largest made-up units */
else
{
if( dist_in_light_years < 9.9)
snprintf( buff, 8, "%4.1fxLY", dist_in_light_years);
else
snprintf( buff, 8, "%4.0fxLY", dist_in_light_years);
buff[4] = si_prefixes[idx];
}
}
else
{
if( dist_in_light_years > 99.999) /* " 1234LY" */
fmt = "%5.0fLY";
else if( dist_in_light_years > 9.999) /* " 12.3LY" */
fmt = "%5.1fLY";
else if( dist_in_light_years > .999)
fmt = "%5.2fLY"; /* " 1.23LY" */
else
fmt = "%5.3fLY"; /* " .123LY" */
snprintf( buff, 8, fmt, dist_in_light_years);
}
}
else
show_dist_in_au( buff, dist_in_au);
*buff = ' '; /* remove leading zero for small amts */
}
}
/* Input velocity is in km/s. If it's greater than about */
/* three times the speed of light, we show it in units of c. */
/* Of course, this will never happen with real objects; I */
/* added it for debugging purposes. */
static void format_velocity_in_buff( char *buff, double vel)
{
const char *format;
if( vel < 9.999 && vel > -9.999)
format = "%7.3f";
else if( vel < 99.999 && vel > -99.999)
format = "%7.2f";
else if( vel < 999.9 && vel > -999.9)
format = "%7.1f";
else if( vel < 999999. && vel > -999999.)
format = "%7.0f";
else /* show velocity in terms of speed of light. */
{
vel /= SPEED_OF_LIGHT;
if( vel < 99.999 && vel > -99.999)
format = "%6.1fc";
else if( vel < 999999. && vel > -999999.)
format = "%6.0fc";
else /* we give up; it's too fast */
format = " !!!!!!";
}
snprintf( buff, 8, format, vel);
}
static void ra_dec_to_alt_az_2( const int planet, const DPT *ra_dec, DPT *alt_az,
const DPT *latlon, const double jd_utc, double *hour_angle)
{
double matrix[9], vect[3], vect_out[3];
polar3_to_cartesian( vect, -ra_dec->x, ra_dec->y);
calc_planet_orientation( planet, 0, jd_utc, matrix);
spin_matrix( matrix, matrix + 3, latlon->x);
if( hour_angle)
*hour_angle = atan2( -dot_product( vect, matrix + 3), dot_product( vect, matrix));
spin_matrix( matrix, matrix + 6, PI / 2. - latlon->y);
precess_vector( matrix, vect, vect_out);
alt_az->x = atan2( vect_out[1], vect_out[0]);
alt_az->y = asine( vect_out[2]);
}
/* Rob Matson asked about having the program produce ECF (Earth-Centered
Fixed) coordinates, in geometric lat/lon/altitude form. This 'ground
track' option in ephemerides has since been expanded to allow geodetic
output, with the possibility of creating such ephemerides from other
planets as well. */
double find_lat_lon_alt( const double ut, const double *ivect,
const int planet_no, double *lat_lon, const bool geometric);
/* 'get_step_size' parses input text to get a step size in days, so that */
/* '4h' becomes .16667 days, '30m' becomes 1/48 day, and '10s' becomes */
/* 10/(24*60*60) days. The units (days, hours, minutes, or seconds) are */
/* returned in 'step_units' if the input pointer is non-NULL. The number */
/* of digits necessary is returned in 'step_digits' if that pointer is */
/* non-NULL. Both are used to ensure correct time format in ephemeris */
/* output; that is, if the step size is (say) .05d, the output times */
/* ought to be in a format such as '2009 Mar 8.34', two places in days. */
double get_step_size( const char *stepsize, char *step_units, int *step_digits)
{
double step = 0.;
char units = 'd';
if( !strncmp( stepsize, "Obs", 3) || *stepsize == 't') /* dummy value */
step = 1e-6;
if( *stepsize == 'a')
{
step = 1e-6;
if( step_digits)
*step_digits = 0;
}
if( sscanf( stepsize, "%lf%c", &step, &units) >= 1)
if( step)
{
if( step_digits)
{
const char *tptr = strchr( stepsize, '.');
*step_digits = 0;
if( tptr)
{
tptr++;
while( isdigit( *tptr++))
(*step_digits)++;
}
#ifdef OBSOLETE_METHOD
double tval = fabs( step);
for( *step_digits = 0; tval < .999; (*step_digits)++)
tval *= 10.;
#endif
}
units = tolower( units);
if( step_units)
*step_units = units;
switch( units)
{
case 'd':
break;
case 'h':
step /= hours_per_day;
break;
case 'm':
step /= minutes_per_day;
break;
case 's':
step /= seconds_per_day;
break;
case 'w':
step *= 7.;
break;
case 'y':
step *= 365.25;
break;
}
}
return( step);
}
static double centralize_ang_around_zero( double ang)
{
ang = fmod( ang, PI + PI);
if( ang > PI)
ang -= PI + PI;
else if( ang <= -PI)
ang += PI + PI;
return( ang);
}
typedef struct
{
double ra, dec, jd, r;
double sun_obj, sun_earth;
} obj_location_t;
static void setup_obj_loc( obj_location_t *p, double *orbit,
const size_t n_orbits, const double epoch_jd, const char *mpc_code)
{
size_t i, j;
mpc_code_t cinfo;
double obs_posn[3];
int planet_no = 3;
assert( p->jd > 2e+6);
assert( p->jd < 3e+6);
assert( mpc_code);
planet_no = get_observer_data( mpc_code, NULL, &cinfo);
compute_observer_loc( p->jd, planet_no, cinfo.rho_cos_phi, cinfo.rho_sin_phi,
cinfo.lon, obs_posn);
for( i = 0; i < n_orbits; i++)
{
double topo[3], time_lag;
if( !mpc_code)
p[i].r = 0.;
assert( p[i].r >= 0.);
assert( p[i].r < 100.);
integrate_orbit( orbit, epoch_jd, p->jd);
time_lag = p[i].r / AU_PER_DAY;
for( j = 0; j < 3; j++)
topo[j] = orbit[j] - obs_posn[j] - time_lag * orbit[j + 3];
ecliptic_to_equatorial( topo);
p[i].ra = atan2( topo[1], topo[0]);
p[i].r = vector3_length( topo);
p[i].dec = asin( topo[2] / p[i].r);
p[i].sun_earth = vector3_length( obs_posn);
p[i].sun_obj = vector3_length( orbit);
orbit += 6;
}
}
/* Here, we take the computed sky brightness from the Schaefer-Krisciunas
model and add in the contribution from another source, such as light
pollution and/or galactic background. For both of those, I don't really
have a good concept of the adjustment for each band; the 'multipliers'
are somewhat ad hoc. */
static void adjust_sky_brightness_for_added_light_source(
BRIGHTNESS_DATA *bdata, const double mags_per_arcsec_squared)
{
const double brightness =
exp( -0.4 * LOG_10 * (11.055 + mags_per_arcsec_squared));
size_t i;
const double multipliers[5] = { .01, .01, .2, 1.0, 1.0 };
for( i = 0; i < 5; i++)
bdata->brightness[i] += brightness * multipliers[i];
}
#pragma pack( 1)
typedef struct
{
double ra, dec, jd;
double height, width, tilt;
uint32_t file_offset;
char obscode[4];
char file_number;
} field_location_t;
typedef struct
{
double height, width;
double min_jd, max_jd;
char obscode[4], file_number;
} field_group_t;
#pragma pack( )
/* In searching for fields, we may be interested in fields _within_ a certain
range of dates, or those _outside_ that range. We signal the former with
max_jd > min_jd. We signal the latter by reversing them (min_jd > max_jd.) */
static inline bool jd_is_in_range( const double jd, const double min_jd,
const double max_jd)
{
if( max_jd > min_jd) /* looking for fields _within_ this range */
return( jd > min_jd && jd < max_jd);
else /* looking for fields _outside_ this range */
return( jd < min_jd || jd > max_jd);
}
static int put_ephemeris_posn_angle_sigma( char *obuff, const double dist,
const double posn_ang, const bool computer_friendly)
{
int integer_posn_ang =
(int)( floor( -posn_ang * 180. / PI + .5)) % 180;
const double dist_in_arcsec = dist * 3600. * 180. / PI;
char resid_buff[9];
if( integer_posn_ang < 0)
integer_posn_ang += 180;
if( computer_friendly)
snprintf( resid_buff, sizeof( resid_buff), " %6u",
(unsigned)dist_in_arcsec);
else
{
put_residual_into_text( resid_buff, dist_in_arcsec,
RESIDUAL_FORMAT_OVERPRECISE);
resid_buff[5] = '\0';
}
snprintf( obuff, 13, "%s %3d", resid_buff + 1, integer_posn_ang);
return( integer_posn_ang);
}
/* Old MSVCs and OpenWATCOM lack erf() and many other math functions: */
#if defined( _MSC_VER) && (_MSC_VER < 1800) || defined( __WATCOMC__)
double erf( double x); /* orb_fun2.cpp */
#endif
#define SWAP( A, B, TEMP) { TEMP = A; A = B; B = TEMP; }
/* At present, this assumes a 'nominal' position in p[0] and a one-sigma
variant in p[1]. We figure out the range, in sigmas, of that line within
the rectangle defined by 'field' (keeping in mind that the line may miss
the rectangle entirely, and usually does). But if the line of variation
_does_ go through the triangle, running from sigma1 to sigma2, then we
evaluate the probability that the object is on that field as the area
under the normal curve between sigma1 and sigma2, and return that.
For cases where we don't have variant orbits (n_objs == 1), we just
set up a really low difference and are basically just checking to see if
the nominal position is on the field. (Which, with one orbit, is all
we can do anyway.)
For objects with low positional uncertainty, that probability will
usually be essentially 1 or 0. If the uncertainty is close to the field
size, you'll start to see "maybe it's on the field and maybe it isn't"
cases.
TO BE DONE: figure out how to extend this to non-covariance (SR) cases.
I've ideas for this... but first, the (more common) covariance case. */
static double precovery_in_field( const field_location_t *field,
const obj_location_t *p, const unsigned n_objs,
const double margin)
{
double sigma1 = -10., sigma2 = 10.;
const double d_ra = (n_objs > 1 ? p[1].ra - p[0].ra : 1e-8);
const double d_dec = (n_objs > 1 ? p[1].dec - p[0].dec : 1e-8);
double sig1, sig2, temp, size;
const double sqrt_2 =
1.414213562373095048801688724209698078569671875376948073176679737990732;
size = (field->width / 2. + margin) / cos( field->dec);
sig1 = centralize_ang_around_zero( field->ra + size - p[0].ra) / d_ra;
sig2 = sig1 - 2 * size / d_ra;
if( sig1 > sig2)
SWAP( sig1, sig2, temp);
if( sigma1 < sig1)
sigma1 = sig1;
if( sigma2 > sig2)
sigma2 = sig2;
size = field->height / 2. + margin;
sig1 = (field->dec + size - p[0].dec) / d_dec;
sig2 = (field->dec - size - p[0].dec) / d_dec;
if( sig1 > sig2)
SWAP( sig1, sig2, temp);
if( sigma1 < sig1)
sigma1 = sig1;
if( sigma2 > sig2)
sigma2 = sig2;
if( sigma1 >= sigma2)
return( 0.);
else
return( (erf( sigma2 / sqrt_2) - erf( sigma1 / sqrt_2)) * .5);
}
static void show_precovery_extent( char *obuff, const obj_location_t *objs,
const int n_objs)
{
*obuff = '\0';
if( n_objs == 2)
{
double dist, posn_ang;
calc_dist_and_posn_ang( &objs[0].ra, &objs[1].ra,
&dist, &posn_ang);
put_ephemeris_posn_angle_sigma( obuff, dist, posn_ang, true);
}
}
/* See 'precover.txt' for information on what's going on here. */
#define FIELD_BUFF_N 1024
#define COMPRESSED_FIELD_SIZE 18
static void extract_field( field_location_t *field, const char *buff,
const field_group_t *groups)
{
int32_t array[4];
assert( buff[16] >= 0);
assert( strlen( groups->obscode) == 3);
groups += buff[16];
assert( strlen( groups->obscode) == 3);
memcpy( array, buff, 4 * sizeof( int32_t));
field->ra = (double)array[0] * 2. * PI / 2e+9;
field->dec = (double)array[1] * PI / 2e+9;
field->jd = groups->min_jd + (groups->max_jd - groups->min_jd)
* (double)array[2] / 2e+9;
field->file_offset = array[3];
field->tilt = (double)buff[17] * PI / 256.;
field->height = groups->height;
field->width = groups->width;
field->file_number = groups->file_number;
strlcpy_error( field->obscode, groups->obscode);
}
static int find_precovery_plates( OBSERVE *obs, const int n_obs,
const char *idx_filename,
FILE *ofile, const double *orbit,
const int n_orbits, double epoch_jd,
const double min_jd, const double max_jd,
const double limiting_mag)
{
FILE *ifile, *original_file = NULL;
int current_file_number = -1;
double *orbi, stepsize = 1., max_jd_available, min_jd_available;
obj_location_t *p1, *p2, *p3;
int n_fields_read, n;
const double abs_mag = calc_absolute_magnitude( obs, n_obs);
char *buff;
/* Slightly easier to work with 'bit set means included' : */
const int inclusion = atoi( get_environment_ptr( "FIELD_INCLUSION")) ^ 3;
const bool show_base_60 = (*get_environment_ptr( "FIELD_DEBUG") != '\0');
size_t n_groups;
field_group_t *groups;
if( !ofile)
return( -1);
ifile = fopen_ext( idx_filename, "crb");
if( !ifile)
{
debug_printf( "Couldn't open %s\n", idx_filename);
return( -2);
}
p1 = (obj_location_t *)calloc( 3 * n_orbits, sizeof( obj_location_t));
p2 = p1 + n_orbits;
p3 = p2 + n_orbits;
buff = (char *)calloc( FIELD_BUFF_N, COMPRESSED_FIELD_SIZE);
assert( buff);
if( !fgets( buff, 100, ifile))
return( -4);
n_groups = (size_t)atoi( buff);
assert( n_groups);
groups = (field_group_t *)calloc( n_groups, sizeof( field_group_t));
assert( groups);
if( fread( groups, sizeof( field_group_t), n_groups, ifile) != n_groups)
return( -3);
orbi = (double *)malloc( 2 * n_orbit_params * n_orbits * sizeof( double));
memcpy( orbi, orbit, n_orbit_params * n_orbits * sizeof( double));
while( (n_fields_read = (int)fread( buff, COMPRESSED_FIELD_SIZE, FIELD_BUFF_N, ifile)) > 0)
for( n = 0; n < n_fields_read; n++)
{
field_location_t field;
extract_field( &field, buff + n * COMPRESSED_FIELD_SIZE, groups);
if( jd_is_in_range( field.jd, min_jd, max_jd))
{
double fraction, mag;
double margin = .1;
const double jdt = field.jd + td_minus_utc( field.jd) / seconds_per_day;
bool possibly_within_field = false;
double prob;
int i;
while( jdt < p1->jd || jdt > p2->jd)
{
const double new_p2_jd = ceil( (jdt - .5) / stepsize) * stepsize + .5;
const double scale_factor = 2.;
if( new_p2_jd == p1->jd)
memcpy( p2, p1, n_orbits * sizeof( obj_location_t));
else if( new_p2_jd != p2->jd)
{
p2->jd = new_p2_jd;
setup_obj_loc( p2, orbi, n_orbits, epoch_jd, "500");
epoch_jd = p2->jd;
}
while( stepsize > p2->r * scale_factor)
stepsize /= 2.;
while( stepsize < p2->r * scale_factor)
stepsize *= 2.;
p1->jd = new_p2_jd - stepsize;
setup_obj_loc( p1, orbi, n_orbits, epoch_jd, "500");
epoch_jd = p1->jd;
}
fraction = (jdt - p1->jd) / stepsize;
for( i = 0; i < n_orbits; i++) /* compute approx RA/decs */
{
const double delta_ra = p2[i].ra - p1[i].ra;
p3[i].ra = p1[i].ra + fraction * centralize_ang_around_zero( delta_ra);
p3[i].dec = p1[i].dec + fraction * (p2[i].dec - p1[i].dec);
}
margin += EARTH_RADIUS_IN_AU / p1->r;
mag = abs_mag + calc_obs_magnitude(
p2->sun_obj, p2->r, p2->sun_earth, NULL);
if( mag < limiting_mag && precovery_in_field( &field, p3, n_orbits, margin) > .01)
{ /* approx posn is on plate; compute */
double *temp_orbit = orbi + n_orbit_params * n_orbits;
memcpy( temp_orbit, orbi, n_orbit_params * n_orbits * sizeof( double));
memcpy( p3, p2, n_orbits * sizeof( obj_location_t));
p3->jd = jdt;
setup_obj_loc( p3, temp_orbit, n_orbits, epoch_jd, field.obscode);
possibly_within_field = true;
}
if( mag < limiting_mag && possibly_within_field
&& (prob = precovery_in_field( &field, p3, n_orbits, 0.)) > .1)
{
char time_buff[40], buff[200];
int i;
bool matches_an_observation = false;
bool show_it = true;
double obj_ra = p3->ra, obj_dec = p3->dec;
full_ctime( time_buff, field.jd, FULL_CTIME_YMD
| FULL_CTIME_LEADING_ZEROES
| FULL_CTIME_MONTHS_AS_DIGITS | FULL_CTIME_TENTHS_SEC);
obj_ra = centralize_ang( obj_ra);
for( i = 0; i < n_obs; i++)
if( fabs( obs[i].jd - jdt) < 1.e-3
&& !strcmp( field.obscode, obs[i].mpc_code))
matches_an_observation = true;
if( matches_an_observation)
show_it = ((inclusion & 2) != 0);
else
show_it = ((inclusion & 1) != 0);
if( show_it)
{
obj_ra *= 180. / PI;
obj_dec *= 180. / PI;
if( !show_base_60)
snprintf( buff, sizeof( buff), "%8.4f %8.4f",
obj_ra, obj_dec);
else
{
output_angle_to_buff( buff, obj_ra / 15., 3);
buff[12] = ' ';
output_signed_angle_to_buff( buff + 13, obj_dec, 2);
}
fprintf( ofile, "%c %s %4.1f %s %s",
(matches_an_observation ? '*' : ' '), buff, mag,
time_buff, field.obscode);
if( current_file_number != field.file_number)
{
char filename[20];
current_file_number = field.file_number;
snprintf( filename, sizeof( filename), "css_%d.csv",
current_file_number);
if( original_file)
fclose( original_file);
original_file = fopen_ext( filename, "crb");
if( !original_file)
fprintf( ofile, "'%s' not opened\n", filename);
}
show_precovery_extent( buff, p1, n_orbits);
snprintf_append( buff, sizeof( buff), " %.3f ", prob);
fprintf( ofile, "%s", buff);
if( original_file)
{
fseek( original_file, field.file_offset, SEEK_SET);
if( fgets_trimmed( buff, sizeof( buff), original_file))
{
for( i = 0; buff[i]; i++)
if( buff[i] == ',')
buff[i] = ' ';
fprintf( ofile, " %s", buff);
}
else
fprintf( ofile, "File %d: seeked to %ld and failed",
(int)field.file_number, (long)field.file_offset);
}
fprintf( ofile, "\n");
}
}
}
}
fclose( ifile);
max_jd_available = 0.;
min_jd_available = 3e+7;
for( size_t i = 0; i < n_groups; i++)
{
if( max_jd_available < groups[i].max_jd)
max_jd_available = groups[i].max_jd;
if( min_jd_available > groups[i].min_jd)
min_jd_available = groups[i].min_jd;
}
full_ctime( buff, min_jd_available, 0);
full_ctime( buff + 80, max_jd_available, 0);
fprintf( ofile, "Pointing data covers %s to %s\n", buff, buff + 80);
free( buff);
free( groups);
if( original_file)
fclose( original_file);
free( orbi);
free( p1);
return( 0);
}
/* In the following, I'm assuming an object with H=0 and albedo=100% to
have a diameter of 1300 km. Return value is in meters. */
double diameter_from_abs_mag( const double abs_mag,
const double optical_albedo)
{
return( 1300. * 1000. * pow( .1, abs_mag / 5.) / sqrt( optical_albedo));
}
#define RADAR_DATA struct radar_data
RADAR_DATA
{
double power_in_watts;
double system_temp_deg_k;
double gain, radar_constant;
double altitude_limit;
};
static inline int get_radar_data( const char *mpc_code, RADAR_DATA *rdata)
{
char tbuff[20];
const char *tptr;
int rval = -1;
memset( rdata, 0, sizeof( RADAR_DATA));
snprintf( tbuff, sizeof( tbuff), "RADAR_%.3s", mpc_code);
tptr = get_environment_ptr( tbuff);
if( tptr)
if( sscanf( tptr, "%lf,%lf,%lf,%lf,%lf",
&rdata->power_in_watts, &rdata->system_temp_deg_k,
&rdata->gain, &rdata->altitude_limit,
&rdata->radar_constant) == 5)
rval = 0;
rdata->altitude_limit *= PI / 180.;
return( rval);
}
/* In computing radar SNR, we need to either measure the rotation period
(if we're lucky, and somebody does a light curve) or take an educated guess
at it, as a function of absolute magnitude. In general, smaller rocks
spin faster than bigger rocks.
I asked about this, and Mike Nolan replied : "I tend to use 4h for
larger than H=21, 1 for H=21-25, and .25 for H > 25. We don't really know
the distribution for the small stuff, as the biases are pretty big." To
which Lance Benner replied : "We've been adopting a somewhat more
conservative value of P = 2.1 h for objects with H < 22. This is based
on the observed distribution of NEA rotation periods (although there are a
couple of exceptions). For smaller objects, a similar cutoff doesn't seem
to exist, but rapid rotators are relatively common, so we adopt P = 0.5h."
In the following, I went with a three-hour period for H<=21 and a .3
hour period for H>=25, linearly interpolating for 21 < H < 25.
Fortunately, SNR/day in the formula below depends on the square root of
the period. If we're out by a factor of two on our guess, it'll mess up the
SNR/day by a factor of the square root of two. I'd guess that errors due to
under- or over-estimating the albedo or H probably cause much more trouble.
*/
static double guessed_rotation_period_in_hours( const double abs_mag)
{
double rval;
const double big_limit = 21., big_period = 3.; /* H=21 rocks spin in 3h */
const double small_limit = 25., small_period = 0.3;
/* little H=25 rocks spin in a mere 18 minutes */
if( abs_mag < big_limit)
rval = big_period;
else if( abs_mag < small_limit)
rval = small_period +
(big_period - small_period) * (small_limit - abs_mag) / (small_limit - big_limit);
else /* small, fast-spinning rocks */
rval = small_period;
return( rval);
}
/* In a private communication, Lance Benner wrote:
"...The signal-to-noise ratio is proportional to:
[(Ptx)(radar albedo)(D^3/2)(P^1/2)(t^1/2)] <-- numerator
------------------------------------------
[(r^4)*(Tsys)] <-- denominator
where Ptx is the transmitter power, the radar albedo is the radar cross section
divided by the projected area of the object, D is the diameter, P is the
rotation period, t is the integration time, r is the distance from the
telescope, and Tsys is the system temperature."
Implicitly, this is also all multiplied by a gain factor, and a
constant known in this code as 'radar_constant'.
He also mentioned that Arecibo operates at about 500 kW, Tsys = 25 K,
gain = 10 K/Jy; Goldstone at 450 kW, Tsys = 15, gain = 0.94. These
values are enshrined in the RADAR_251 and RADAR_253 lines in
'environ.dat', along with the 'radar_constant' values. I got those
essentially by guessing, then scaling them until they matched values in
radar planning documents. (Unfortunately, Arecibo is now at 350 kW and
gain=7 K/Jy due to Maria damage.)
See also Lance's comments at
https://groups.io/g/mpml/message/28412
and an excellent page on the subject at
http://www.naic.edu/~pradar/detect.php
Lance also noted that there's also a more subtle dependence due to the subradar
latitude (you get a better echo if the pole is pointing straight at the radar).
Jean-Luc Margot's page:
http://www2.ess.ucla.edu/~jlm/research/NEAs/intro.html
has a graphic showing this dependence. A 20-meter object with a four-hour
period and albedo=.1, at a distance of .1 AU, has SNR/day = 1.
For Goldstone, the SNR is about 1/20 of this (from JLM's page; I think
this assumes Arecibo going at 900 kW.) The same page shows a dropoff in SNR
due to declination: the above formula holds at dec=+18, but SNR drops to
zero at dec=-1 or dec=37. In reality, it should be a drop in _altitude_ :
i.e., Arecibo sees "perfectly" at the zenith, and degrades as you drop from
there. Mike Nolan tells me (private e-mail communication) that the width is
about 19.5 degrees, so that Arecibo can "see" down to about altitude = 70.5
degrees. The drop factor isn't given (and is probably empirically derived),
but it looks a lot like
SNR( alt) = SNR( zenith) * ((90 - alt)/19.5) ^ .25, 70.5 < alt < 90
Or something like that, perhaps with a different exponent: a function
equal to one at alt=90 degrees and zero at alt=70.5 degrees, with roughly
the right behavior in between.
See further comments in 'environ.def'.
Other quantities of interest for radar: the 'number of runs', i.e.,