QISG学习之-在图层上画图

研究过源码的人都知道 QGIS对于在地图上的功能操作都是通过QgsMapTool来管理的，有一篇博客有详细讲解:http://blog.youkuaiyun.com/deirjie/article/details/50878670

所以要实现画图也很简单了。

首先继承QgsMapTool，这里提供了各种坐标转换，我们当然非常需要。

#ifndef MEASURETOOL_H

#define MEASURETOOL_H

#include <qgsmaptool.h>

#include <QList>

class QgsDistanceArea;

class QgsMapCanvas;

class QgsRubberBand;

class  MeasureTool : public QgsMapTool

{

    Q_OBJECT

  public:

    MeasureTool( QgsMapCanvas* canvas, bool measureArea );

    ~MeasureTool();

    //virtual Flags flags() const override { return QgsMapTool::AllowZoomRect; }

    //! returns whether measuring distance or area

    bool measureArea() { return mMeasureArea; }

    //! When we have added our last point, and not following

    bool done() { return mDone; }

    //! Reset and start new

    void restart();

    //! Add new point

    void addPoint( const QgsPoint &point );

    //! Returns reference to array of the points

    const QList<QgsPoint>& points();

    // Inherited from QgsMapTool

    //! Mouse move event for overriding

    virtual void canvasMoveEvent( QgsMapMouseEvent* e ) override;

    //! Mouse press event for overriding

    virtual void canvasPressEvent( QgsMapMouseEvent* e ) override;

    //! Mouse release event for overriding

    virtual void canvasReleaseEvent( QgsMapMouseEvent* e ) override;

    //! called when set as currently active map tool

    virtual void activate() override;

    //! called when map tool is being deactivated

    virtual void deactivate() override;

    virtual void keyPressEvent( QKeyEvent* e ) override;

  public slots:

    //! updates the projections we're using

    void updateSettings();

  protected:

    QList<QgsPoint> mPoints;

    //! Rubberband widget tracking the lines being drawn

    QgsRubberBand *mRubberBand;

    //! Rubberband widget tracking the added nodes to line

    QgsRubberBand *mRubberBandPoints;

    //! indicates whether we're measuring distances or areas

    bool mMeasureArea;

    //! indicates whether we've just done a right mouse click

    bool mDone;

    //! indicates whether we've recently warned the user about having the wrong

    // project projection

    bool mWrongProjectProjection;

    //! Destination CoordinateReferenceSystem used by the MapCanvas

    QgsCoordinateReferenceSystem mDestinationCrs;

    //! Returns the snapped (map) coordinate

    //@param p (pixel) coordinate

    QgsPoint snapPoint( const QPoint& p );

    /** Removes the last vertex from mRubberBand*/

    void undo();

};

#endif // MEASURETOOL_H

源文件：

#include "qgsdistancearea.h"

#include "qgslogger.h"

#include "qgsmapcanvas.h"

#include "qgsmaprenderer.h"

#include "qgsmaptopixel.h"

#include "qgsrubberband.h"

#include "qgsvectorlayer.h"

#include "qgssnappingutils.h"

#include "qgstolerance.h"

#include "qgscursors.h"

#include "qgsmessagelog.h"

#include "MeasureTool.h"

#include <QMessageBox>

#include <QMouseEvent>

#include <QSettings>

MeasureTool::MeasureTool( QgsMapCanvas* canvas, bool measureArea )

    : QgsMapTool( canvas )

    , mWrongProjectProjection( false )

{

  mMeasureArea = measureArea;

  mRubberBand = new QgsRubberBand( canvas, mMeasureArea ? QGis::Polygon : QGis::Line );

  mRubberBand->setIcon(QgsRubberBand::ICON_FULL_BOX);

  mRubberBandPoints = new QgsRubberBand( canvas, QGis::Point );

  QPixmap myCrossHairQPixmap = QPixmap(( const char ** ) cross_hair_cursor );

  mCursor = QCursor( myCrossHairQPixmap, 8, 8 );

  mDone = true;

  // Append point we will move

  mPoints.append( QgsPoint( 0, 0 ) );

  mDestinationCrs = canvas->mapSettings().destinationCrs();

//  mDialog = new QgsMeasureDialog( this );

//  mDialog->setWindowFlags( mDialog->windowFlags() | Qt::Tool );

//  mDialog->restorePosition();

  connect( canvas, SIGNAL( destinationCrsChanged() ),

           this, SLOT( updateSettings() ) );

}

MeasureTool::~MeasureTool()

{

 // delete mDialog;

  delete mRubberBand;

  delete mRubberBandPoints;

}

const QList<QgsPoint>& MeasureTool::points()

{

  return mPoints;

}

void MeasureTool::activate()

{

 // mDialog->show();

  QgsMapTool::activate();

  // ensure that we have correct settings

  updateSettings();

  // If we suspect that they have data that is projected, yet the

  // map CRS is set to a geographic one, warn them.

  if ( mCanvas->mapSettings().destinationCrs().geographicFlag() &&

       ( mCanvas->extent().height() > 360 ||

         mCanvas->extent().width() > 720 ) )

  {

    QMessageBox::warning( nullptr, tr( "Incorrect measure results" ),

                          tr( "<p>This map is defined with a geographic coordinate system "

                              "(latitude/longitude) "

                              "but the map extents suggests that it is actually a projected "

                              "coordinate system (e.g., Mercator). "

                              "If so, the results from line or area measurements will be "

                              "incorrect.</p>"

                              "<p>To fix this, explicitly set an appropriate map coordinate "

                              "system using the <tt>Settings:Project Properties</tt> menu." ) );

    mWrongProjectProjection = true;

  }

}

void MeasureTool::deactivate()

{

 // mDialog->hide();

  QgsMapTool::deactivate();

}

void MeasureTool::restart()

{

  mPoints.clear();

  mRubberBand->reset( mMeasureArea ? QGis::Polygon : QGis::Line );

  mRubberBandPoints->reset( QGis::Point );

  mDone = true;

  mWrongProjectProjection = false;

}

void MeasureTool::updateSettings()

{

  QSettings settings;

  int myRed = settings.value( "/qgis/default_measure_color_red", 222 ).toInt();

  int myGreen = settings.value( "/qgis/default_measure_color_green", 155 ).toInt();

  int myBlue = settings.value( "/qgis/default_measure_color_blue", 67 ).toInt();

  mRubberBand->setColor( QColor( myRed, myGreen, myBlue, 100 ) );

  mRubberBand->setWidth( 3 );

  mRubberBandPoints->setIcon( QgsRubberBand::ICON_CIRCLE );

  mRubberBandPoints->setIconSize( 10 );

  mRubberBandPoints->setColor( QColor( myRed, myGreen, myBlue, 150 ) );

  // Reproject the points to the new destination CoordinateReferenceSystem

  if ( mRubberBand->size() > 0 && mDestinationCrs != mCanvas->mapSettings().destinationCrs() )

  {

    QList<QgsPoint> points = mPoints;

    bool lastDone = mDone;

   // mDialog->restart();

    mDone = lastDone;

    QgsCoordinateTransform ct( mDestinationCrs, mCanvas->mapSettings().destinationCrs() );

    Q_FOREACH ( const QgsPoint& previousPoint, points )

    {

      try

      {

        QgsPoint point = ct.transform( previousPoint );

        mPoints.append( point );

        mRubberBand->addPoint( point, false );

        mRubberBandPoints->addPoint( point, false );

      }

      catch ( QgsCsException &cse )

      {

        QgsMessageLog::logMessage( QString( "Transform error caught at the MeasureTool: %1" ).arg( cse.what() ) );

      }

    }

    mRubberBand->updatePosition();

    mRubberBand->update();

    mRubberBandPoints->updatePosition();

    mRubberBandPoints->update();

  }

  mDestinationCrs = mCanvas->mapSettings().destinationCrs();

  //mDialog->updateSettings();

  if ( !mDone && mRubberBand->size() > 0 )

  {

    mRubberBand->addPoint( mPoints.last() );

   // mDialog->addPoint( mPoints.last() );

  }

  if ( mRubberBand->size() > 0 )

  {

    mRubberBand->setVisible( true );

    mRubberBandPoints->setVisible( true );

  }

}

//

void MeasureTool::canvasPressEvent( QgsMapMouseEvent* e )

{

  Q_UNUSED( e );

}

void MeasureTool::canvasMoveEvent( QgsMapMouseEvent* e )

{

  if ( ! mDone )

  {

    QgsPoint point = snapPoint( e->pos() );

    mRubberBand->movePoint( point );

   // mDialog->mouseMove( point );

  }

}

void MeasureTool::canvasReleaseEvent( QgsMapMouseEvent* e )

{

  QgsPoint point = snapPoint( e->pos() );

  if ( mDone ) // if we have stopped measuring any mouse click restart measuring

  {

    //mDialog->restart();

  }

  if ( e->button() == Qt::RightButton ) // if we clicked the right button we stop measuring

  {

    mDone = true;

  }

  else if ( e->button() == Qt::LeftButton )

  {

    mDone = false;

  }

  // we always add the clicked point to the measuring feature

  addPoint( point );

 // mDialog->show();

}

void MeasureTool::undo()

{

  if ( mRubberBand )

  {

    if ( mPoints.size() < 1 )

    {

      return;

    }

    if ( mPoints.size() == 1 )

    {

      //removing first point, so restart everything

      restart();

     // mDialog->restart();

    }

    else

    {

      //remove second last point from line band, and last point from points band

      mRubberBand->removePoint( -2, true );

      mRubberBandPoints->removePoint( -1, true );

      mPoints.removeLast();

     // mDialog->removeLastPoint();

    }

  }

}

void MeasureTool::keyPressEvent( QKeyEvent* e )

{

  if (( e->key() == Qt::Key_Backspace || e->key() == Qt::Key_Delete ) )

  {

    if ( !mDone )

    {

      undo();

    }

    // Override default shortcut management in MapCanvas

    e->ignore();

  }

}

void MeasureTool::addPoint( const QgsPoint &point )

{

  QgsDebugMsg( "point=" + point.toString() );

  // don't add points with the same coordinates

  if ( !mPoints.isEmpty() && mPoints.last() == point )

  {

    return;

  }

  QgsPoint pnt( point );

  // Append point that we will be moving.

  mPoints.append( pnt );

  mRubberBand->addPoint( point );

  mRubberBandPoints->addPoint( point );

  if ( ! mDone )    // Prevent the insertion of a new item in segments measure table

  {

    //mDialog->addPoint( point );

  }

}

QgsPoint MeasureTool::snapPoint( const QPoint& p )

{

  QgsPointLocator::Match m = mCanvas->snappingUtils()->snapToMap( p );

  return m.isValid() ? m.point() : mCanvas->getCoordinateTransform()->toMapCoordinates( p );

}

使用

 线段：

MeasureTool* addFeatureTool = new MeasureTool( mapCanvas, false);

mapCanvas->setMapTool( addFeatureTool );

面积：

MeasureTool* addFeatureTool = new MeasureTool( mapCanvas, true);

mapCanvas->setMapTool( addFeatureTool );