Kstars

starcorrespondence.h
1/*
2 SPDX-FileCopyrightText: 2020 Hy Murveit <hy@murveit.com>
3
4 SPDX-License-Identifier: GPL-2.0-or-later
5*/
6
7#pragma once
8
9#include <QObject>
10#include <QList>
11#include <QVector>
12#include <QVector2D>
13
14#include "fitsviewer/fitsdata.h"
15#include "vect.h"
16
17/*
18 * This class is useful to track a guide star by noting its position relative to other stars.
19 * It is intended to be resilient to translation, a bit of positional noise, and slight field rotation.
20 * The class is initialized with a set of reference (x,y) positions from stars, where one is
21 * designated a guide star. Then, given a set of new input star positions, it determines a mapping
22 * of the new stars to the references. Some reference stars may not be in the new star group, and
23 * there may be new stars that don't appear in the references. However, the guide star must appear
24 * in both sets for this to be successful.
25 */
26
27class StarCorrespondence
28{
29 public:
30 // Initializes with reference stars.
31 // One of the stars with index guideStar is a special "guide star".
32 StarCorrespondence(const QList<Edge> &stars, int guideStar);
33 StarCorrespondence();
34 ~StarCorrespondence() {}
35
36 // If the default constructor was called, then initialize must be called with the
37 // reference star positions and the index in stars of the guideStar.
38 void initialize(const QList<Edge> &stars, int guideStar);
39
40 // Clears the references.
41 void reset();
42
43 // Associate the input stars with the reference stars.
44 // StarMap[i] will contain the index of a reference star that corresponds to the ith star.
45 // Some input stars may have no reference (starMap->at(i) == -1), and some references may
46 // not correspond to any input stars. There will be no star-reference mapping with
47 // distance longer than maxDistance. If adapt is true, the input positions are used
48 // to incrementally adapt the reference positions.
49 Edge find(const QList<Edge> &stars, double maxDistance, QVector<int> *starMap, bool adapt = true, double minFraction = 0.5);
50
51 // Returns the number of reference stars.
52 int size() const
53 {
54 return references.size();
55 }
56
57 // Return a reference to the ith reference star. Caller's responsiblity
58 // to make sure i >= 0 && i < references.size();
59 // Recompute the reference coordinates as we may adapt them.
60 Edge reference(int i) const
61 {
62 Edge star = references[i];
63 star.x = references[guideStarIndex].x + guideStarOffsets[i].x;
64 star.y = references[guideStarIndex].y + guideStarOffsets[i].y;
65 return star;
66 }
67 QVector2D offset(int i) const
68 {
69 QVector2D offset;
70 offset.setX(guideStarOffsets[i].x);
71 offset.setY(guideStarOffsets[i].y);
72 return offset;
73 }
74
75 int guideStar() const
76 {
77 return guideStarIndex;
78 }
79
80 void setAllowMissingGuideStar(bool value = true)
81 {
82 allowMissingGuideStar = value;
83 }
84
85 void setImageSize(int width, int height)
86 {
87 imageWidth = width;
88 imageHeight = height;
89 }
90
91 int getNumReferencesFound() const
92 {
93 return m_NumReferencesFound;
94 }
95
96 private:
97 // The Offsets structure is used to keep the positions of the reference stars
98 // relative to the guide star.
99 struct Offsets
100 {
101 double x; // The x position of the star (in pixels), relative to the guide star.
102 double y; // The y position of the star (in pixels), relative to the guide star.
103
104 Offsets(double x_, double y_) : x(x_), y(y_) {}
105 Offsets() : x(0), y(0) {} // RPi compiler required this constructor.
106 };
107
108 // Update the reference-star offsets given the new star positions.
109 // The adaption is similar to a 25-sample moving average.
110 void initializeAdaptation();
111 void adaptOffsets(const QList<Edge> &stars, const QVector<int> &starMap);
112
113 // Utility used by find. Useful for iterating when the guide star is missing.
114 int findInternal(const QList<Edge> &stars, double maxDistance, QVector<int> *starMap,
115 int guideStarIndex, const QVector<Offsets> &offsets,
116 int *numFound, int *numNotFound, double minFraction) const;
117
118 // Used to when guide star is missing. Creates offsets as if other stars were the guide star.
119 void makeOffsets(const QVector<Offsets> &offsets, QVector<Offsets> *targetOffsets, int targetStar) const;
120
121 // When the guide star is missing, but star correspondence was successful, use the positions
122 // of the stars that were found to create a virtual guide star--inferring a guide star position
123 // using the offsets from the (unfound) guide star to the stars that were found.
124 // Offsets are offsets that were created for a new "substitude guide star".
125 // StarMap is the map made for that substitude by findInternal().
126 // Offset is the offset from the original guide star to that substitute guide star.
127 Edge inventStarPosition(const QList<Edge> &stars, const QVector<int> &starMap,
128 QVector<Offsets> offsets, Offsets offset) const;
129
130 // Finds the star closest to x,y. Returns the index in sortedStars.
131 // sortedStars should be sorted in x, which allows for a speedup in search.
132 int findClosestStar(double x, double y, const QList<Edge> sortedStars,
133 double maxDistance, double *distance) const;
134
135 // The offsets of the reference stars relative to the guide star.
136 QVector<Offsets> guideStarOffsets;
137
138 // Size stats for the reference stars.
139 QVector<float> referenceSums;
140 QVector<float> referenceNumPixels;
141
142 QList<Edge> references; // The original reference stars.
143 int guideStarIndex; // The index of the guide star in references.
144 bool initialized = false; // Set to true once the references and guideStar index has been set.
145
146 // If this is true, it will attempt star correspondence even if the guide star is missing.
147 bool allowMissingGuideStar { false };
148
149 // IIR filter parameter used to adapt offsets.
150 double alpha;
151
152 // Setting imageWidth and height can speed up searching for stars in an image
153 // by eliminating positions far outside the image.
154 int imageWidth { 100000000 };
155 int imageHeight { 100000000 };
156
157 // Number of references found in last call to find().
158 int m_NumReferencesFound { 0 };
159
160 // A copy of the original reference offsets used so that the values don't move too far.
161 QVector<Offsets> originalGuideStarOffsets;
162};
163
qsizetype size() const const
void setX(float x)
void setY(float y)
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