QGIS API Documentation  3.23.0-Master (7c4a6de034)
qgsalgorithmnearestneighbouranalysis.cpp
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1 /***************************************************************************
2  qgsalgorithmnearestneighbouranalysis.cpp
3  ---------------------
4  begin : December 2019
5  copyright : (C) 2019 by Alexander Bruy
6  email : alexander dot bruy at gmail dot com
7  ***************************************************************************/
8 
9 /***************************************************************************
10  * *
11  * This program is free software; you can redistribute it and/or modify *
12  * it under the terms of the GNU General Public License as published by *
13  * the Free Software Foundation; either version 2 of the License, or *
14  * (at your option) any later version. *
15  * *
16  ***************************************************************************/
17 
19 #include "qgsapplication.h"
20 #include "qgsdistancearea.h"
21 #include <QTextStream>
22 
24 
25 QString QgsNearestNeighbourAnalysisAlgorithm::name() const
26 {
27  return QStringLiteral( "nearestneighbouranalysis" );
28 }
29 
30 QString QgsNearestNeighbourAnalysisAlgorithm::displayName() const
31 {
32  return QObject::tr( "Nearest neighbour analysis" );
33 }
34 
35 QStringList QgsNearestNeighbourAnalysisAlgorithm::tags() const
36 {
37  return QObject::tr( "point,node,vertex,nearest,neighbour,distance" ).split( ',' );
38 }
39 
40 QString QgsNearestNeighbourAnalysisAlgorithm::group() const
41 {
42  return QObject::tr( "Vector analysis" );
43 }
44 
45 QString QgsNearestNeighbourAnalysisAlgorithm::groupId() const
46 {
47  return QStringLiteral( "vectoranalysis" );
48 }
49 
50 QString QgsNearestNeighbourAnalysisAlgorithm::shortHelpString() const
51 {
52  return QObject::tr( "This algorithm performs nearest neighbor analysis for a point layer.\n\n"
53  "The output describes how the data are distributed (clustered, randomly or distributed).\n\n"
54  "Output is generated as an HTML file with the computed statistical values." );
55 }
56 
57 QString QgsNearestNeighbourAnalysisAlgorithm::svgIconPath() const
58 {
59  return QgsApplication::iconPath( QStringLiteral( "/algorithms/mAlgorithmNearestNeighbour.svg" ) );
60 }
61 
62 QIcon QgsNearestNeighbourAnalysisAlgorithm::icon() const
63 {
64  return QgsApplication::getThemeIcon( QStringLiteral( "/algorithms/mAlgorithmNearestNeighbour.svg" ) );
65 }
66 
67 QgsNearestNeighbourAnalysisAlgorithm *QgsNearestNeighbourAnalysisAlgorithm::createInstance() const
68 {
69  return new QgsNearestNeighbourAnalysisAlgorithm();
70 }
71 
72 void QgsNearestNeighbourAnalysisAlgorithm::initAlgorithm( const QVariantMap & )
73 {
74  addParameter( new QgsProcessingParameterFeatureSource( QStringLiteral( "INPUT" ), QObject::tr( "Input layer" ), QList< int >() << QgsProcessing::TypeVectorPoint ) );
75  addParameter( new QgsProcessingParameterFileDestination( QStringLiteral( "OUTPUT_HTML_FILE" ), QObject::tr( "Nearest neighbour" ),
76  QObject::tr( "HTML files (*.html *.HTML)" ), QVariant(), true ) );
77  addOutput( new QgsProcessingOutputNumber( QStringLiteral( "OBSERVED_MD" ), QObject::tr( "Observed mean distance" ) ) );
78  addOutput( new QgsProcessingOutputNumber( QStringLiteral( "EXPECTED_MD" ), QObject::tr( "Expected mean distance" ) ) );
79  addOutput( new QgsProcessingOutputNumber( QStringLiteral( "NN_INDEX" ), QObject::tr( "Nearest neighbour index" ) ) );
80  addOutput( new QgsProcessingOutputNumber( QStringLiteral( "POINT_COUNT" ), QObject::tr( "Number of points" ) ) );
81  addOutput( new QgsProcessingOutputNumber( QStringLiteral( "Z_SCORE" ), QObject::tr( "Z-score" ) ) );
82 }
83 
84 QVariantMap QgsNearestNeighbourAnalysisAlgorithm::processAlgorithm( const QVariantMap &parameters, QgsProcessingContext &context, QgsProcessingFeedback *feedback )
85 {
86  std::unique_ptr< QgsProcessingFeatureSource > source( parameterAsSource( parameters, QStringLiteral( "INPUT" ), context ) );
87  if ( !source )
88  throw QgsProcessingException( invalidSourceError( parameters, QStringLiteral( "INPUT" ) ) );
89 
90  const QString outputFile = parameterAsFileOutput( parameters, QStringLiteral( "OUTPUT_HTML_FILE" ), context );
91 
92  const QgsSpatialIndex spatialIndex( *source, feedback, QgsSpatialIndex::FlagStoreFeatureGeometries );
93  QgsDistanceArea da;
94  da.setSourceCrs( source->sourceCrs(), context.transformContext() );
95  da.setEllipsoid( context.ellipsoid() );
96 
97  const double step = source->featureCount() ? 100.0 / source->featureCount() : 1;
98  QgsFeatureIterator it = source->getFeatures( QgsFeatureRequest().setSubsetOfAttributes( QList< int >() ) );
99 
100  const QgsFeatureRequest request;
101  const QgsFeature neighbour;
102  double sumDist = 0.0;
103  const double area = source->sourceExtent().width() * source->sourceExtent().height();
104 
105  int i = 0;
106  QgsFeature f;
107  while ( it.nextFeature( f ) )
108  {
109  if ( feedback->isCanceled() )
110  {
111  break;
112  }
113 
114  const QgsFeatureId neighbourId = spatialIndex.nearestNeighbor( f.geometry().asPoint(), 2 ).at( 1 );
115  sumDist += da.measureLine( spatialIndex.geometry( neighbourId ).asPoint(), f.geometry().asPoint() );
116 
117  i++;
118  feedback->setProgress( i * step );
119  }
120 
121  const long long count = source->featureCount() > 0 ? source->featureCount() : 1;
122  const double observedDistance = sumDist / count;
123  const double expectedDistance = 0.5 / std::sqrt( count / area );
124  const double nnIndex = observedDistance / expectedDistance;
125  const double se = 0.26136 / std::sqrt( std::pow( count, 2 ) / area );
126  const double zScore = ( observedDistance - expectedDistance ) / se;
127 
128  QVariantMap outputs;
129  outputs.insert( QStringLiteral( "OBSERVED_MD" ), observedDistance );
130  outputs.insert( QStringLiteral( "EXPECTED_MD" ), expectedDistance );
131  outputs.insert( QStringLiteral( "NN_INDEX" ), nnIndex );
132  outputs.insert( QStringLiteral( "POINT_COUNT" ), count );
133  outputs.insert( QStringLiteral( "Z_SCORE" ), zScore );
134 
135  if ( !outputFile.isEmpty() )
136  {
137  QFile file( outputFile );
138  if ( file.open( QIODevice::WriteOnly | QIODevice::Truncate ) )
139  {
140  QTextStream out( &file );
141 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
142  out.setCodec( "UTF-8" );
143 #endif
144  out << QStringLiteral( "<html><head><meta http-equiv=\"Content-Type\" content=\"text/html;charset=utf-8\"/></head><body>\n" );
145  out << QObject::tr( "<p>Observed mean distance: %1</p>\n" ).arg( observedDistance, 0, 'f', 11 );
146  out << QObject::tr( "<p>Expected mean distance: %1</p>\n" ).arg( expectedDistance, 0, 'f', 11 );
147  out << QObject::tr( "<p>Nearest neighbour index: %1</p>\n" ).arg( nnIndex, 0, 'f', 11 );
148  out << QObject::tr( "<p>Number of points: %1</p>\n" ).arg( count );
149  out << QObject::tr( "<p>Z-Score: %1</p>\n" ).arg( zScore, 0, 'f', 11 );
150  out << QStringLiteral( "</body></html>" );
151 
152  outputs.insert( QStringLiteral( "OUTPUT_HTML_FILE" ), outputFile );
153  }
154  }
155 
156  return outputs;
157 }
158 
static QIcon getThemeIcon(const QString &name, const QColor &fillColor=QColor(), const QColor &strokeColor=QColor())
Helper to get a theme icon.
static QString iconPath(const QString &iconFile)
Returns path to the desired icon file.
A general purpose distance and area calculator, capable of performing ellipsoid based calculations.
double measureLine(const QVector< QgsPointXY > &points) const
Measures the length of a line with multiple segments.
void setSourceCrs(const QgsCoordinateReferenceSystem &crs, const QgsCoordinateTransformContext &context)
Sets source spatial reference system crs.
bool setEllipsoid(const QString &ellipsoid)
Sets the ellipsoid by its acronym.
Wrapper for iterator of features from vector data provider or vector layer.
bool nextFeature(QgsFeature &f)
This class wraps a request for features to a vector layer (or directly its vector data provider).
The feature class encapsulates a single feature including its unique ID, geometry and a list of field...
Definition: qgsfeature.h:56
QgsGeometry geometry
Definition: qgsfeature.h:67
bool isCanceled() const SIP_HOLDGIL
Tells whether the operation has been canceled already.
Definition: qgsfeedback.h:54
void setProgress(double progress)
Sets the current progress for the feedback object.
Definition: qgsfeedback.h:63
QgsPointXY asPoint() const
Returns the contents of the geometry as a 2-dimensional point.
Contains information about the context in which a processing algorithm is executed.
QgsCoordinateTransformContext transformContext() const
Returns the coordinate transform context.
QString ellipsoid() const
Returns the ellipsoid to use for distance and area calculations.
Custom exception class for processing related exceptions.
Definition: qgsexception.h:83
Base class for providing feedback from a processing algorithm.
A numeric output for processing algorithms.
An input feature source (such as vector layers) parameter for processing algorithms.
A generic file based destination parameter, for specifying the destination path for a file (non-map l...
@ TypeVectorPoint
Vector point layers.
Definition: qgsprocessing.h:49
A spatial index for QgsFeature objects.
@ FlagStoreFeatureGeometries
Indicates that the spatial index should also store feature geometries. This requires more memory,...
qint64 QgsFeatureId
64 bit feature ids negative numbers are used for uncommitted/newly added features
Definition: qgsfeatureid.h:28