QwtPolarPlot radius scale

Hello,
I'm looking for how to create my own major and minor ticks on the scaleId
QwtPolar::Radius.
I tried :

Code:

---

if (!d_prefDlg->get_pasZ_Auto()) {
         /* Récupération du pas choisi
         ****************************/
         double pasz = d_prefDlg->get_pasZ();
 
         /* Ajustement des extrema
         ************************/
         nivmax = pasz*ceil(nivmax/pasz);
         nivmin = pasz*floor(nivmin/pasz);
 
         /* Nombre de pas
         ***************/
         double nbPas = ((int)(((nivmax-nivmin)/pasz)));
 
         /* Recherche du meilleur pas principal
         *************************************/
         double major;
         for(int ii=8; ii>1; ii--) {
                 major = floor(nbPas/ii);
                 if (major > 5)
                         break;
         }
         double pasMajor = major*pasz;
         int nbPasminor = floor(pasMajor/pasz);
         d_polarplot->setScale(QwtPolar::Radius,nivmin, nivmax, pasMajor);
         d_polarplot->setScaleMaxMajor(QwtPolar::Radius, major);
         d_polarplot->setScaleMaxMinor(QwtPolar::Radius, nbPasminor);
 
 
         /* Création des pas principaux et secondaires
         ********************************************/
         QList<double> ticksR[QwtScaleDiv::NTickTypes];
         QList<double> &majorTicksR = ticksR[QwtScaleDiv::MajorTick];
         QList<double> &minorTicksR = ticksR[QwtScaleDiv::MinorTick];
         for (double niveau=nivmin; niveau <= nivmax; niveau=niveau+pasz) {
             if (fmod((niveau-nivmin),major*pasz) == 0) {
                 majorTicksR.append(niveau);
             } else {
                 minorTicksR.append(niveau);
             }
         }
 
         QwtScaleDiv myScaleDivR = QwtScaleDiv(majorTicksR.first(),
 majorTicksR.last(), ticksR);
         d_polarplot->setScaleDiv(QwtPolar::Radius, myScaleDivR);
         if (d_polarplot->scaleDiv(QwtPolar::Radius)->isValid() == false)
             Message("Invalide", false);
 
         } else
             d_polarplot->setScale(QwtPolar::Radius,nivmin, nivmax);

---

With nivmin = -93, nivmax=-39 and pasz=3, I should get the following major
ticks :-93,-75,-57 and -39, with 6 minor ticks between 2 major ticks.

But that did'nt work (see attach file).

Thanks for your help

The boundaries and all major and minor ticks of a scale are defined in a QwtScaleDiv object. You can calculate a QwtScaleDiv object in your application code and pass it to the plot using QwtPolarPlot::setScaleDiv().

A plot widget has a scale engine for each scale, that is able to calculate a QwtScaleDiv object from min/max/stepsize ( + max major steps + max minor steps ). QwtPolarPlot::setScale() calculates internally a QwtScaleDiv using the internal scale engine.

Qwt offers two different types of scale engines: a linear and logarithmic one, both based on decades.

The right solution for your problem depends on whether your plot offers a navigation ( zooming, panning, ... ). If not you can manually calculate your ticks and use QwtPolarPlot::setScaleDiv() - not using the internal scale engine.

But if your plot offers navigation you need to implement an algorithm, that calculates ticks for any random boundaries for your -93 +i * 18 based scale system ( what ticks do you expect from a range -90 -> -89 ? ) in a class derived from QwtScaleEngine.

Uwe

Hello,

I resolved my problem. The QwtPolar documentation indicates that using setScaleDiv the autoscalling is disabled, but in fact you should disable the autoscaling in the QwtPolarGrid:

Code:

---

this->d_grid = new QwtPolarGrid();
if (!d_prefDlg->get_pasZ_Auto()) 
    d_grid->setGridAttribute(QwtPolarGrid::AutoScaling,false);
else
    d_grid->setGridAttribute(QwtPolarGrid::AutoScaling,true);
 
....
d_grid->attach(d_polarplot);

---

Thank a lot