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Archive for August 6th, 2015

Corner detection on Strokes and Strokes annotations on Matplotlib

August 6th, 2015 2 comments

Following my proposal for the Google Summer of Code 2015, an algorithm to detect corners on strokes was implemented and it is going to be polished and tested with a template matching classifier. This implementation follows Wolin approach in his paper: “ShortStraw: A Simple and Effective Corner Finder for Polylines” which can be downloaded from: http://faculty.cse.tamu.edu/hammond/publications/pdf/2008WolinSBIM.pdf

A brief explanation of the algorithm consists on sampling each one of the points in order to have equal distance between them. Then a window of +/-3 points is used and the average or mean of the distances is calculated. The distance between the initial point and the last point of the window form a straw. The straw is smaller in the cases that the window of points contain a corner.

corners strokesFrom the figure can be seen that pretty much corners are being detected. However a post processing still needs to be performed. In addition, a stroke canvas behavior was added to a figure canvas widget so annotations can be done on top of the graphs as can be seen in the figure below. The yellow background and the blue dots are just debugging information.

backend_kivy with annotations

backend_kivy and backend_kivyagg working with matplotlib 1.4.3, python2 and python3.

August 6th, 2015 No comments

Initially backend_kivy was implemented using matplotlib 1.5.1dev which is an unstable release. Small modifications were made based on the changes matplotlib has between 1.4.3 (stable) and 1.5.1dev. Some of the main points that were updated were the generation of MathText and the lines rendering in draw_path. Additionally in the case of backend_kivyagg a read-only memory view was sent from the agg renderer to the kivy backend, a writable copy had to be created due to an exception in cython for loading read-only buffers. Some other improvements involve a bug when the application was being closed which was fixed by adding an on_close event in the app and setting the global var app to None, another improvement is the generation of images from the plots. In the case of backend_kivy the figure canvas widget is being exported to png using the export_to_png(filename). A bug was reported when the FigureCanvasKivy is added to a BorderLayout and the window is resized. For instance if we have a button on top of the figure canvas, when resized the figure canvas is resized to the size of the window moving the button up but then is scaled down again and the dimensions are right. This arises in the backend_kivy due to a small delay that keeps the calculation of the positions in this case of the button out of the canvas. In backend_kivyagg this does not happen due to a fast transition so the button position is calculated correctly. (still an open issue and working on that for backend_kivy.)

Navigation Toolbar with matplotlib events connected

August 6th, 2015 No comments

NavigationToolbar is the last visual aspect from the backend that has been added with all the possible events connected to matplotlib. The main changes performed on the implementation involved to connect each one of the toolbar elements to the respective matplotlib calls. Additionally, the figure canvas is separated from the toolbar and both are children of a Float Layout inside an app generated via pyplot. The FigureCanvasKivy can be called independently of the NavigationToolbar but not in the opposite direction.

# updated version of the toolbar generation.
def _init_toolbar(self):
        basedir = os.path.join(rcParams['datapath'], 'images')
        actionview = ActionView()
        actionprevious = ActionPrevious(title="Navigation", with_previous=False)
        actionoverflow = ActionOverflow()
        actionview.add_widget(actionprevious)
        actionview.add_widget(actionoverflow)
        actionview.use_separator = True
        self.actionbar.add_widget(actionview)
        for text, tooltip_text, image_file, callback in self.toolitems:
            if text is None:
                actionview.add_widget(ActionSeparator())
                continue
            fname = os.path.join(basedir, image_file + '.png')
            if text in ['Pan', 'Zoom']:
                action_button = ActionToggleButton(text=text, icon=fname)
            else:
                action_button = ActionButton(text=text, icon=fname)
            action_button.bind(on_press=getattr(self, callback))
            actionview.add_widget(action_button)

Navigation Toolbar Kivy

For matplotlib users the interface can look very familiar. However, I consider a brief explanation is necessary on the function of each button:

Home: Resets the plot axes to the initial state.
Left: Undo an operation performed.
Right: Redo an operation performed.
Pan: Allows to drag the plot.
Zoom: Allows to define a rectangular area to zoom in.
Configure: Not implemented yet but, loads a pop up for repositioning elements.
Save: Loads a Save Dialog to generate an image.
Configure and Save will be added at some point the next week.

Categories: GSOC2015, kivy, matplotlib Tags: , ,