Select ScatterPlotItem points using ROI

[Jorge Gil]

Hi,

Is it possible to use a ROI to select ScatterplotItemPoints?

The PyQtGraph examples only show ROI interacting with Raster images, not point data.

Thank you,

Jorge

[Luke Campagnola]

On Sun, Mar 30, 2014 at 1:27 PM, Jorge Gil <gil....@gmail.com> wrote:

Is it possible to use a ROI to select ScatterplotItemPoints?

The PyQtGraph examples only show ROI interacting with Raster images, not point data.

In the most general case (for arbitrarily-shaped ROIs), I think you just have to ask whether each point is found inside the ROI shape

For example:

# get ROI shape in coordinate system of the scatter plot

roiShape = roi.mapToItem(scatterPlot, roi.shape())

# Get list of all points inside shape

selected = [pt for pt in scatterPlotPoints if roiShape.contains(pt)]

For simple ROI shapes, you might be able to do something more efficient, like find all points within certain x/y ranges for a rectangular ROI.

Let me know if you need more help with this.

Luke

[Jorge Gil]

Dear Luke,

Thanks for the reply.
From it I understand that there are no built-in functions for point in ROI shape check.

I'll have to decide on the best way to do it considering that I might have many thousands of points and it will get too slow. Might even stick with the rectangle for performance and simplicity.

Once I get back to this problem, and if I need more help, I'll let you know.

Thanks,
Jorge

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[Luke Campagnola]

On Tue, Apr 1, 2014 at 10:52 AM, Jorge Gil <gil....@gmail.com> wrote:

From it I understand that there are no built-in functions for point in ROI shape check.

In the example I provided, QGraphicsItem.shape() returns a QPainterPath, which has a .contains() method for testing whether a point is inside the path. See:

http://qt-project.org/doc/qt-4.8/qgraphicsitem.html#shape

http://qt-project.org/doc/qt-4.8/qpainterpath.html#contains

I'll have to decide on the best way to do it considering that I might have many thousands of points and it will get too slow. 

Might even stick with the rectangle for performance and simplicity.

Try it first, then optimize. A compromise might be to first select all points within the bounding rectangle of the shape (see QPainterPath.boundingRect) because this can be done quickly, and then do the more expensive QPainterPath.contains() with that smaller subset of points. 

[Jorge Gil]

Dear Luke,

Thanks for the examples and links to the documentation, I hadn't realised you were using QGraphicsItem.shape() and contains()! I'm a Qt beginner, as well as pyqtgraph...

I'll follow your suggestions, it sounds very feasible this way.

Best,
Jorge

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