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36 * \page page_module_selection_insolidangle Selection method: insolidangle
38 * This method selects a subset of particles that are located in a solid
39 * angle defined by a center and a set of points.
40 * The solid angle is constructed as a union of small cones whose axis
41 * goes through the center and a point.
42 * So there's such a cone for each position, and a
43 * point is in the solid angle if it lies within any of these cones.
44 * The width of the cones can be adjusted.
46 * The method is implemented by partitioning the surface of the unit sphere
47 * into bins using the polar coordinates \f$(\theta, \phi)\f$.
48 * The partitioning is always uniform in the zenith angle \f$\theta\f$,
49 * while the partitioning in the azimuthal angle \f$\phi\f$ varies.
50 * For each reference point, the unit vector from the center to the point
51 * is constructed, and it is stored in all the bins that overlap with the
52 * cone defined by the point.
53 * Bins that are completely covered by a single cone are marked as such.
54 * Checking whether a point is in the solid angle is then straightforward
55 * with this data structure: one finds the bin that corresponds to the point,
56 * and checks whether the bin is completely covered. If it is not, one
57 * additionally needs to check whether it is within the specified cutoff of
58 * any of the stored points.
60 * The above construction gives quite a lot of flexibility for constructing
61 * the bins without modifying the rest of the code.
62 * The current (quite inefficient) implementation is discussed below, but
63 * it should be optimized to get the most out of the code.
65 * The current way of constructing the bins constructs the boundaries
66 * statically: the bin size in the zenith direction is set to approximately
67 * half the angle cutoff, and the bins in the azimuthal direction have
68 * sizes such that the shortest edge of the bin is approximately equal to
69 * half the angle cutoff (for the regions close to the poles, a single bin
71 * Each reference point is then added to the bins as follows:
72 * -# Find the zenith angle range that is spanned by the cone centered at the
73 * point (this is simple addition/subtraction).
74 * -# Calculate the maximal span of the cone in the azimuthal direction using
76 * \f[\sin \Delta \phi_{max} = \frac{\sin \alpha}{\sin \theta}\f]
77 * (a sine formula in spherical coordinates),
78 * where \f$\alpha\f$ is the width of the cone and \f$\theta\f$ is the
79 * zenith angle of the cone center.
80 * Similarly, the zenith angle at which this extent is achieved is
82 * \f[\cos \theta_{max} = \frac{\cos \theta}{\cos \alpha}\f]
83 * (Pythagoras's theorem in spherical coordinates).
84 * -# For each zenith angle bin that is at least partially covered by the
85 * cone, calculate the span of the cone at the edges using
86 * \f[\sin^2 \frac{\Delta \phi}{2} = \frac{\sin^2 \frac{\alpha}{2} - \sin^2 \frac{\theta - \theta'}{2}}{\sin \theta \sin \theta'}\f]
87 * (distance in spherical geometry),
88 * where \f$\theta'\f$ is the zenith angle of the bin edge.
89 * Treat zenith angle bins that are completely covered by the cone (in the
90 * case that the cone is centered close to the pole) as a special case.
91 * -# Using the values calculated above, loop through the azimuthal bins that
92 * are partially or completely covered by the cone and update them.
94 * The total solid angle (for covered fraction calculations) is estimated by
95 * taking the total area of completely covered bins plus
96 * half the area of partially covered bins.
97 * The second one is an approximation, but should give reasonable estimates
98 * for the averages as well as in cases where the bin size is small.
102 * Implements the \ref sm_insolidangle "insolidangle" selection method.
105 * The implementation could be optimized quite a bit.
108 * Move the covered fraction stuff somewhere else and make it more generic
109 * (along the lines it is handled in selection.h and trajana.h in the old C
112 * \author Teemu Murtola <teemu.murtola@gmail.com>
113 * \ingroup module_selection
119 #include "gromacs/legacyheaders/macros.h"
120 #include "gromacs/legacyheaders/maths.h"
121 #include "gromacs/legacyheaders/pbc.h"
122 #include "gromacs/legacyheaders/physics.h"
123 #include "gromacs/legacyheaders/smalloc.h"
124 #include "gromacs/legacyheaders/vec.h"
126 #include "gromacs/selection/indexutil.h"
127 #include "gromacs/selection/position.h"
128 #include "gromacs/selection/selection.h"
129 #include "gromacs/selection/selmethod.h"
130 #include "gromacs/utility/exceptions.h"
139 * Internal data structure for the \p insolidangle selection method.
141 * \see \c t_partition
143 * \ingroup module_selection
147 /** Left edge of the partition. */
149 /** Bin index corresponding to this partition. */
155 * Internal data structure for the \p insolidangle selection method.
157 * Describes the surface partitioning within one slice along the zenith angle.
158 * The slice from azimuthal angle \p p[i].left to \p p[i+1].left belongs to
161 * \ingroup module_selection
165 /** Number of partition items (\p p contains \p n+1 items). */
167 /** Array of partition edges and corresponding bins. */
173 * Internal data structure for the \p insolidangle selection method.
175 * Contains the reference points that partially cover a certain region on the
176 * surface of the unit sphere.
177 * If \p n is -1, the whole region described by the bin is covered.
179 * \ingroup module_selection
183 /** Number of points in the array \p x, -1 if whole bin covered. */
185 /** Number of elements allocated for \p x. */
187 /** Array of points that partially cover the bin. */
189 } t_spheresurfacebin;
193 * Data structure for the \p insolidangle selection method.
195 * All angle values are in the units of radians.
197 * \ingroup module_selection
201 /** Center of the solid angle. */
202 gmx_ana_pos_t center;
203 /** Positions that span the solid angle. */
207 /** Estimate of the covered fraction. */
210 /** Cutoff for the cosine (equals cos(angcut)). */
212 /** Bin size to be used as the target bin size when constructing the bins. */
215 /** Number of bins in the \p tbin array. */
217 /** Size of one bin in the zenith angle direction. */
219 /** Array of zenith angle slices. */
221 /** Number of elements allocated for the \p bin array. */
223 /** Number of elements used in the \p bin array. */
225 /** Array of individual bins. */
226 t_spheresurfacebin *bin;
227 } t_methoddata_insolidangle;
229 /** Allocates data for the \p insolidangle selection method. */
231 init_data_insolidangle(int npar, gmx_ana_selparam_t *param);
232 /** Initializes the \p insolidangle selection method. */
234 init_insolidangle(t_topology *top, int npar, gmx_ana_selparam_t *param, void *data);
235 /** Frees the data allocated for the \p insolidangle selection method. */
237 free_data_insolidangle(void *data);
238 /** Initializes the evaluation of the \p insolidangle selection method for a frame. */
240 init_frame_insolidangle(t_topology *top, t_trxframe *fr, t_pbc *pbc, void *data);
241 /** Internal helper function for evaluate_insolidangle(). */
243 accept_insolidangle(rvec x, t_pbc *pbc, void *data);
244 /** Evaluates the \p insolidangle selection method. */
246 evaluate_insolidangle(t_topology *top, t_trxframe *fr, t_pbc *pbc,
247 gmx_ana_pos_t *pos, gmx_ana_selvalue_t *out, void *data);
249 /** Calculates the distance between unit vectors. */
251 sph_distc(rvec x1, rvec x2);
252 /** Does a binary search on a \p t_partition to find a bin for a value. */
254 find_partition_bin(t_partition *p, real value);
255 /** Finds a bin that corresponds to a location on the unit sphere surface. */
257 find_surface_bin(t_methoddata_insolidangle *surf, rvec x);
258 /** Clears/initializes the bins on the unit sphere surface. */
260 clear_surface_points(t_methoddata_insolidangle *surf);
261 /** Frees memory allocated for storing the reference points in the surface bins. */
263 free_surface_points(t_methoddata_insolidangle *surf);
264 /** Adds a reference point to a given bin. */
266 add_surface_point(t_methoddata_insolidangle *surf, int tbin, int pbin, rvec x);
267 /** Marks a bin as completely covered. */
269 mark_surface_covered(t_methoddata_insolidangle *surf, int tbin, int pbin);
270 /** Helper function for store_surface_point() to update a single zenith angle bin. */
272 update_surface_bin(t_methoddata_insolidangle *surf, int tbin,
273 real phi, real pdelta1, real pdelta2, real pdeltamax,
275 /** Adds a single reference point and updates the surface bins. */
277 store_surface_point(t_methoddata_insolidangle *surf, rvec x);
278 /** Optimizes the surface bins for faster searching. */
280 optimize_surface_points(t_methoddata_insolidangle *surf);
281 /** Estimates the area covered by the reference cones. */
283 estimate_covered_fraction(t_methoddata_insolidangle *surf);
284 /** Checks whether a point lies within a solid angle. */
286 is_surface_covered(t_methoddata_insolidangle *surf, rvec x);
288 /** Parameters for the \p insolidangle selection method. */
289 static gmx_ana_selparam_t smparams_insolidangle[] = {
290 {"center", {POS_VALUE, 1, {NULL}}, NULL, SPAR_DYNAMIC},
291 {"span", {POS_VALUE, -1, {NULL}}, NULL, SPAR_DYNAMIC | SPAR_VARNUM},
292 {"cutoff", {REAL_VALUE, 1, {NULL}}, NULL, SPAR_OPTIONAL},
295 /** Help text for the \p insolidangle selection method. */
296 static const char *help_insolidangle[] = {
297 "SELECTING ATOMS IN A SOLID ANGLE[PAR]",
299 "[TT]insolidangle center POS span POS_EXPR [cutoff REAL][tt][PAR]",
301 "This keyword selects atoms that are within [TT]REAL[tt] degrees",
302 "(default=5) of any position in [TT]POS_EXPR[tt] as seen from [TT]POS[tt]",
303 "a position expression that evaluates to a single position), i.e., atoms",
304 "in the solid angle spanned by the positions in [TT]POS_EXPR[tt] and",
305 "centered at [TT]POS[tt].[PAR]"
307 "Technically, the solid angle is constructed as a union of small cones",
308 "whose tip is at [TT]POS[tt] and the axis goes through a point in",
309 "[TT]POS_EXPR[tt]. There is such a cone for each position in",
310 "[TT]POS_EXPR[tt], and point is in the solid angle if it lies within any",
311 "of these cones. The cutoff determines the width of the cones.",
314 /** \internal Selection method data for the \p insolidangle method. */
315 gmx_ana_selmethod_t sm_insolidangle = {
316 "insolidangle", GROUP_VALUE, SMETH_DYNAMIC,
317 asize(smparams_insolidangle), smparams_insolidangle,
318 &init_data_insolidangle,
322 &free_data_insolidangle,
323 &init_frame_insolidangle,
325 &evaluate_insolidangle,
326 {"insolidangle center POS span POS_EXPR [cutoff REAL]",
327 asize(help_insolidangle), help_insolidangle},
331 * \param[in] npar Not used (should be 3).
332 * \param[in,out] param Method parameters (should point to
333 * \ref smparams_insolidangle).
334 * \returns Pointer to the allocated data (\ref t_methoddata_insolidangle).
336 * Allocates memory for a \ref t_methoddata_insolidangle structure and
337 * initializes the parameter as follows:
338 * - \p center defines the value for t_methoddata_insolidangle::center.
339 * - \p span defines the value for t_methoddata_insolidangle::span.
340 * - \p cutoff defines the value for t_methoddata_insolidangle::angcut.
343 init_data_insolidangle(int npar, gmx_ana_selparam_t *param)
345 t_methoddata_insolidangle *data = new t_methoddata_insolidangle();
349 data->distccut = 0.0;
350 data->targetbinsize = 0.0;
353 data->tbinsize = 0.0;
359 param[0].val.u.p = &data->center;
360 param[1].val.u.p = &data->span;
361 param[2].val.u.r = &data->angcut;
366 * \param top Not used.
367 * \param npar Not used.
368 * \param param Not used.
369 * \param data Pointer to \ref t_methoddata_insolidangle to initialize.
370 * \returns 0 on success, -1 on failure.
372 * Converts t_methoddata_insolidangle::angcut to radians and allocates
373 * and allocates memory for the bins used during the evaluation.
376 init_insolidangle(t_topology *top, int npar, gmx_ana_selparam_t *param, void *data)
378 t_methoddata_insolidangle *surf = (t_methoddata_insolidangle *)data;
381 if (surf->angcut <= 0)
383 GMX_THROW(gmx::InvalidInputError("Angle cutoff should be > 0"));
386 surf->angcut *= DEG2RAD;
388 surf->distccut = -cos(surf->angcut);
389 surf->targetbinsize = surf->angcut / 2;
390 surf->ntbins = static_cast<int>(M_PI / surf->targetbinsize);
391 surf->tbinsize = (180.0 / surf->ntbins)*DEG2RAD;
393 snew(surf->tbin, static_cast<int>(M_PI / surf->tbinsize) + 1);
395 for (i = 0; i < surf->ntbins; ++i)
397 c = static_cast<int>(max(sin(surf->tbinsize*i),
398 sin(surf->tbinsize*(i+1)))
399 * M_2PI / surf->targetbinsize) + 1;
400 snew(surf->tbin[i].p, c+1);
404 snew(surf->bin, surf->maxbins);
408 * \param data Data to free (should point to a \ref t_methoddata_insolidangle).
410 * Frees the memory allocated for \c t_methoddata_insolidangle::center and
411 * \c t_methoddata_insolidangle::span, as well as the memory for the internal
415 free_data_insolidangle(void *data)
417 t_methoddata_insolidangle *d = (t_methoddata_insolidangle *)data;
422 for (i = 0; i < d->ntbins; ++i)
428 free_surface_points(d);
434 * \param[in] top Not used.
435 * \param[in] fr Current frame.
436 * \param[in] pbc PBC structure.
437 * \param data Should point to a \ref t_methoddata_insolidangle.
439 * Creates a lookup structure that enables fast queries of whether a point
440 * is within the solid angle or not.
443 init_frame_insolidangle(t_topology *top, t_trxframe *fr, t_pbc *pbc, void *data)
445 t_methoddata_insolidangle *d = (t_methoddata_insolidangle *)data;
449 free_surface_points(d);
450 clear_surface_points(d);
451 for (i = 0; i < d->span.count(); ++i)
455 pbc_dx(pbc, d->span.x[i], d->center.x[0], dx);
459 rvec_sub(d->span.x[i], d->center.x[0], dx);
462 store_surface_point(d, dx);
464 optimize_surface_points(d);
469 * \param[in] x Test point.
470 * \param[in] pbc PBC data (if NULL, no PBC are used).
471 * \param[in] data Pointer to a \c t_methoddata_insolidangle data structure.
472 * \returns true if \p x is within the solid angle, false otherwise.
475 accept_insolidangle(rvec x, t_pbc *pbc, void *data)
477 t_methoddata_insolidangle *d = (t_methoddata_insolidangle *)data;
482 pbc_dx(pbc, x, d->center.x[0], dx);
486 rvec_sub(x, d->center.x[0], dx);
489 return is_surface_covered(d, dx);
493 * See sel_updatefunc() for description of the parameters.
494 * \p data should point to a \c t_methoddata_insolidangle.
496 * Calculates which atoms in \p g are within the solid angle spanned by
497 * \c t_methoddata_insolidangle::span and centered at
498 * \c t_methoddata_insolidangle::center, and stores the result in \p out->u.g.
501 evaluate_insolidangle(t_topology *top, t_trxframe *fr, t_pbc *pbc,
502 gmx_ana_pos_t *pos, gmx_ana_selvalue_t *out, void *data)
505 for (int b = 0; b < pos->count(); ++b)
507 if (accept_insolidangle(pos->x[b], pbc, data))
509 gmx_ana_pos_add_to_group(out->u.g, pos, b);
515 * \param[in] sel Selection element to query.
516 * \returns true if the covered fraction can be estimated for \p sel with
517 * _gmx_selelem_estimate_coverfrac(), false otherwise.
520 _gmx_selelem_can_estimate_cover(const gmx::SelectionTreeElement &sel)
522 if (sel.type == SEL_BOOLEAN && sel.u.boolt == BOOL_OR)
527 bool bDynFound = false;
528 gmx::SelectionTreeElementPointer child = sel.child;
531 if (child->type == SEL_EXPRESSION)
533 if (child->u.expr.method->name == sm_insolidangle.name)
535 if (bFound || bDynFound)
541 else if (child->u.expr.method
542 && (child->u.expr.method->flags & SMETH_DYNAMIC))
551 else if (!_gmx_selelem_can_estimate_cover(*child))
561 * \param[in] sel Selection for which the fraction should be calculated.
562 * \returns Fraction of angles covered by the selection (between zero and one).
564 * The return value is undefined if _gmx_selelem_can_estimate_cover() returns
566 * Should be called after gmx_ana_evaluate_selections() has been called for the
570 _gmx_selelem_estimate_coverfrac(const gmx::SelectionTreeElement &sel)
574 if (sel.type == SEL_EXPRESSION && sel.u.expr.method->name == sm_insolidangle.name)
576 t_methoddata_insolidangle *d = (t_methoddata_insolidangle *)sel.u.expr.mdata;
579 d->cfrac = estimate_covered_fraction(d);
583 if (sel.type == SEL_BOOLEAN && sel.u.boolt == BOOL_NOT)
585 cfrac = _gmx_selelem_estimate_coverfrac(*sel.child);
593 /* Here, we assume that the selection is simple enough */
594 gmx::SelectionTreeElementPointer child = sel.child;
597 cfrac = _gmx_selelem_estimate_coverfrac(*child);
608 * \param[in] x1 Unit vector 1.
609 * \param[in] x2 Unit vector 2.
610 * \returns Minus the dot product of \p x1 and \p x2.
612 * This function is used internally to calculate the distance between the
613 * unit vectors \p x1 and \p x2 to find out whether \p x2 is within the
614 * cone centered at \p x1. Currently, the cosine of the angle is used
615 * for efficiency, and the minus is there to make it behave like a normal
616 * distance (larger values mean longer distances).
619 sph_distc(rvec x1, rvec x2)
621 return -iprod(x1, x2);
625 * \param[in] p Partition to search.
626 * \param[in] value Value to search for.
627 * \returns The partition index in \p p that contains \p value.
629 * If \p value is outside the range of \p p, the first/last index is returned.
630 * Otherwise, the return value \c i satisfies \c p->p[i].left<=value and
631 * \c p->p[i+1].left>value
634 find_partition_bin(t_partition *p, real value)
636 int pmin, pmax, pbin;
638 /* Binary search the partition */
639 pmin = 0; pmax = p->n;
640 while (pmax > pmin + 1)
642 pbin = pmin + (pmax - pmin) / 2;
643 if (p->p[pbin].left <= value)
657 * \param[in] surf Surface data structure to search.
658 * \param[in] x Unit vector to find.
659 * \returns The bin index that contains \p x.
661 * The return value is an index to the \p surf->bin array.
664 find_surface_bin(t_methoddata_insolidangle *surf, rvec x)
670 phi = atan2(x[YY], x[XX]);
671 tbin = static_cast<int>(floor(theta / surf->tbinsize));
672 if (tbin >= surf->ntbins)
674 tbin = surf->ntbins - 1;
676 pbin = find_partition_bin(&surf->tbin[tbin], phi);
677 return surf->tbin[tbin].p[pbin].bin;
681 * \param[in,out] surf Surface data structure.
683 * Clears the reference points from the bins and (re)initializes the edges
684 * of the azimuthal bins.
687 clear_surface_points(t_methoddata_insolidangle *surf)
692 for (i = 0; i < surf->ntbins; ++i)
694 c = static_cast<int>(min(sin(surf->tbinsize*i),
695 sin(surf->tbinsize*(i+1)))
696 * M_2PI / surf->targetbinsize) + 1;
702 for (j = 0; j < c; ++j)
704 surf->tbin[i].p[j].left = -M_PI + j*M_2PI/c - 0.0001;
705 surf->tbin[i].p[j].bin = surf->nbins;
706 surf->bin[surf->nbins].n = 0;
709 surf->tbin[i].p[c].left = M_PI + 0.0001;
710 surf->tbin[i].p[c].bin = -1;
715 * \param[in,out] surf Surface data structure.
718 free_surface_points(t_methoddata_insolidangle *surf)
722 for (i = 0; i < surf->nbins; ++i)
726 sfree(surf->bin[i].x);
728 surf->bin[i].n_alloc = 0;
729 surf->bin[i].x = NULL;
734 * \param[in,out] surf Surface data structure.
735 * \param[in] tbin Bin number in the zenith angle direction.
736 * \param[in] pbin Bin number in the azimuthal angle direction.
737 * \param[in] x Point to store.
740 add_surface_point(t_methoddata_insolidangle *surf, int tbin, int pbin, rvec x)
744 bin = surf->tbin[tbin].p[pbin].bin;
745 /* Return if bin is already completely covered */
746 if (surf->bin[bin].n == -1)
750 /* Allocate more space if necessary */
751 if (surf->bin[bin].n == surf->bin[bin].n_alloc)
753 surf->bin[bin].n_alloc += 10;
754 srenew(surf->bin[bin].x, surf->bin[bin].n_alloc);
756 /* Add the point to the bin */
757 copy_rvec(x, surf->bin[bin].x[surf->bin[bin].n]);
762 * \param[in,out] surf Surface data structure.
763 * \param[in] tbin Bin number in the zenith angle direction.
764 * \param[in] pbin Bin number in the azimuthal angle direction.
767 mark_surface_covered(t_methoddata_insolidangle *surf, int tbin, int pbin)
771 bin = surf->tbin[tbin].p[pbin].bin;
772 surf->bin[bin].n = -1;
776 * \param[in,out] surf Surface data structure.
777 * \param[in] tbin Bin number in the zenith angle direction.
778 * \param[in] phi Azimuthal angle of \p x.
779 * \param[in] pdelta1 Width of the cone at the lower edge of \p tbin.
780 * \param[in] pdelta2 Width of the cone at the uppper edge of \p tbin.
781 * \param[in] pdeltamax Max. width of the cone inside \p tbin.
782 * \param[in] x Point to store (should have unit length).
785 update_surface_bin(t_methoddata_insolidangle *surf, int tbin,
786 real phi, real pdelta1, real pdelta2, real pdeltamax,
789 real pdelta, phi1, phi2;
790 int pbin1, pbin2, pbiniter, pbin;
792 /* Find the edges of the bins affected */
793 pdelta = max(max(pdelta1, pdelta2), pdeltamax);
797 pbin = find_partition_bin(&surf->tbin[tbin], phi1);
802 pbin = find_partition_bin(&surf->tbin[tbin], phi1 + M_2PI);
803 pbin1 = pbin - surf->tbin[tbin].n;
808 pbin2 = find_partition_bin(&surf->tbin[tbin], phi2);
812 pbin2 = find_partition_bin(&surf->tbin[tbin], phi2 - M_2PI);
813 pbin2 += surf->tbin[tbin].n;
816 if (pbin2 - pbin1 > surf->tbin[tbin].n)
818 pbin2 = pbin1 + surf->tbin[tbin].n;
820 /* Find the edges of completely covered region */
821 pdelta = min(pdelta1, pdelta2);
828 /* Loop over all affected bins */
829 for (pbiniter = pbin1; pbiniter != pbin2; ++pbiniter, ++pbin)
831 /* Wrap bin around if end reached */
832 if (pbin == surf->tbin[tbin].n)
838 /* Check if bin is completely covered and update */
839 if (surf->tbin[tbin].p[pbin].left >= phi1
840 && surf->tbin[tbin].p[pbin+1].left <= phi2)
842 mark_surface_covered(surf, tbin, pbin);
846 add_surface_point(surf, tbin, pbin, x);
852 * \param[in,out] surf Surface data structure.
853 * \param[in] x Point to store (should have unit length).
855 * Finds all the bins covered by the cone centered at \p x and calls
856 * update_surface_bin() to update them.
859 store_surface_point(t_methoddata_insolidangle *surf, rvec x)
862 real pdeltamax, tmax;
863 real theta1, theta2, pdelta1, pdelta2;
867 phi = atan2(x[YY], x[XX]);
868 /* Find the maximum extent in the phi direction */
869 if (theta <= surf->angcut)
874 else if (theta >= M_PI - surf->angcut)
881 pdeltamax = asin(sin(surf->angcut) / sin(theta));
882 tmax = acos(cos(theta) / cos(surf->angcut));
884 /* Find the first affected bin */
885 tbin = max(static_cast<int>(floor((theta - surf->angcut) / surf->tbinsize)), 0);
886 theta1 = tbin * surf->tbinsize;
887 if (theta1 < theta - surf->angcut)
895 /* Loop through all affected bins */
896 while (tbin < ceil((theta + surf->angcut) / surf->tbinsize)
897 && tbin < surf->ntbins)
899 /* Calculate the next boundaries */
900 theta2 = (tbin+1) * surf->tbinsize;
901 if (theta2 > theta + surf->angcut)
903 /* The circle is completely outside the cone */
906 else if (theta2 <= -(theta - surf->angcut)
907 || theta2 >= M_2PI - (theta + surf->angcut)
908 || tbin == surf->ntbins - 1)
910 /* The circle is completely inside the cone, or we are in the
911 * 360 degree bin covering the pole. */
916 /* TODO: This formula is numerically unstable if theta is very
917 * close to the pole. In practice, it probably does not matter
918 * much, but it would be nicer to adjust the theta bin boundaries
919 * such that the case above catches this instead of falling through
921 pdelta2 = 2*asin(sqrt(
922 (sqr(sin(surf->angcut/2)) - sqr(sin((theta2-theta)/2))) /
923 (sin(theta) * sin(theta2))));
926 if (tmax >= theta1 && tmax <= theta2)
928 update_surface_bin(surf, tbin, phi, pdelta1, pdelta2, pdeltamax, x);
932 update_surface_bin(surf, tbin, phi, pdelta1, pdelta2, 0, x);
942 * \param[in,out] surf Surface data structure.
944 * Currently, this function does nothing.
947 optimize_surface_points(t_methoddata_insolidangle *surf)
949 /* TODO: Implement */
953 * \param[in] surf Surface data structure.
954 * \returns An estimate for the area covered by the reference points.
957 estimate_covered_fraction(t_methoddata_insolidangle *surf)
960 real cfrac, tfrac, pfrac;
963 for (t = 0; t < surf->ntbins; ++t)
965 tfrac = cos(t * surf->tbinsize) - cos((t+1) * surf->tbinsize);
966 for (p = 0; p < surf->tbin[t].n; ++p)
968 pfrac = surf->tbin[t].p[p+1].left - surf->tbin[t].p[p].left;
969 n = surf->bin[surf->tbin[t].p[p].bin].n;
970 if (n == -1) /* Bin completely covered */
972 cfrac += tfrac * pfrac;
974 else if (n > 0) /* Bin partially covered */
976 cfrac += tfrac * pfrac / 2; /* A rough estimate */
980 return cfrac / (4*M_PI);
984 * \param[in] surf Surface data structure to search.
985 * \param[in] x Unit vector to check.
986 * \returns true if \p x is within the solid angle, false otherwise.
989 is_surface_covered(t_methoddata_insolidangle *surf, rvec x)
993 bin = find_surface_bin(surf, x);
994 /* Check for completely covered bin */
995 if (surf->bin[bin].n == -1)
999 /* Check each point that partially covers the bin */
1000 for (i = 0; i < surf->bin[bin].n; ++i)
1002 if (sph_distc(x, surf->bin[bin].x[i]) < surf->distccut)