c++ - How to draw graph for a trajectory which goes left and right in x axis?

Question

i want to draw a trajectory in x and y of a car in a parking lot.

the trajectory in x is not always in the same direction. sometime the car will go left.

the problem here is: sometime (not always!) the graph will no go left in x axis. You can see the two different result on the image https://imgur.com/Z53fNkt

any idea why?

the image at left is what i expect. at right is the same values , but i continue to plot data a little longer.

void TrackingResultsView::setupTrajectoryPlot()
{
QCustomPlot *customPlot = ui->qcp_trajectory;

customPlot->xAxis2->setVisible(true);
customPlot->xAxis2->setLabel("X-Position (pixel)");
customPlot->xAxis2->setRange(0, mModelPtr->frameSize().width());
customPlot->xAxis2->grid()->setVisible(true);

customPlot->xAxis->setRange(0, mModelPtr->frameSize().width());
customPlot->yAxis->setLabel("Y-Position (pixel)");
customPlot->yAxis->setRange(0, mModelPtr->frameSize().height());
customPlot->yAxis->setRangeReversed(true);

customPlot->yAxis2->setVisible(true);
customPlot->yAxis2->setRange(0, mModelPtr->frameSize().height());
customPlot->yAxis2->grid()->setVisible(true);
customPlot->yAxis2->setRangeReversed(true);
customPlot->addGraph(customPlot->xAxis2, customPlot->yAxis);

QVector<QVector<double>> data = createDataMap(mModelPtr->points());
customPlot->graph()->setData(data.at(0), data.at(1), true);

setTheme(customPlot, false);
}

thank you

(english is not my first langage)

标签： c++qcustomplot

Answer 1

The QCPGraph seems to be used for sorted data with only value per key. From QCustomPlot documentation, it looks like the QCPCurve would be a better match in order to plot a trajectory graph (multiple value for the same key).

From the QCPCurve description:

Unlike QCPGraph, plottables of this type may have multiple points with the same key coordinate, so their visual representation can have loops. This is realized by introducing a third coordinate t, which defines the order of the points described by the other two coordinates x and y.