Is there a way to store x,y coordinates from the brush tool in app designer in an app designer edit field (2021b)?

I have a UI figure in my app with plotted data. With the current version of app designer, I can use the brush tool to obtain x,y coodinates from a point on the plotted data, but I only know how to do this with manual export (to variable, command line, etc.). Is there a way to code a brush tool click (or a button that activates brush tool) that would store the selected x,y values in an edit field in the app?

[Kevin Holly]

Below is a semi-automated approach. However, it does not automate the selection of the data nor the exportation of the selected data.

Create scatterplot

scatter(app.UIAxes,rand(20,1),rand(20,1),'g')
hold(app.UIAxes,'on')
scatter(app.UIAxes,(rand(20,1),rand(20,1),'b')

There is a way to active the brush tool programatically. You can use the brush command as shown below:

brush(app.UIAxes,'on')

This would be the same as clicking on the the paintbrush icon (see image below) that shows up in the top right of the axes.

After selecting the datapoint, you can right click and select "Export Brushed..."

Select data you are interested in and select "OK"

Then choose a variable name for your data.

[RGB85]

Kevin, thanks for the response. The "Export Brushed" approach was what I had come up with as well. Is there not a way to programatically access the x,y data of a single point selected with the brush?

I'm trying to select a single point (using the paintbrush tool) and then click a button within the app to grab those x,y values and store them as a variable. I was hoping to use "app.UIAxes.Children.BrushData" but that comes out in uint8.

Any advice?

Answer 1

[Kevin Holly]

Try the following to recieve the x and y coordinates.

index = app.UIAxes.Children.BrushData;
xcoord = app.UIAxes.Children.XData(logical(index))
ycoord = app.UIAxes.Children.YData(logical(index))

[RGB85]

That's exactly what I needed. Thanks!

[RGB85]

As a follow up, how do I clear the values in brush data? I have several buttons that each pick a specific point using the same form of the code you posted. When I move the brush and activate the second button, I get the error:

Intermediate dot '.' indexing produced a comma-separated list with 2 values, but it must produce a single value when followed by subsequent indexing operations.

It seems like I'm accumulating values in the brush data? I'd like to clear it each time after saving the values.

I've tried manually clearing the brush data (right clicking the point and "clear all brushing") and the following code approaches.

cla(app.UIAxes.Children.BrushData);
%%
app.UIAxes.Children.BrushData.cla
%%
app.UIAxes.Children.BrushData = [];
index = [];

[Kevin Holly]

Maybe you can make all the BrushData values zero?

app.UIAxes.Children.BrushData = uint8(zeros(size(app.UIAxes.Children.BrushData)));

If you knew the location of the datapoints you wanted to select within the array, you could select the datapoints automatically.

 app.UIAxes.Children.BrushData(2)=1; %Let's select the 2nd datapoimt

I created a for loop going through each of the datapoints.

% Run for loop after initially selecting data with brush
for i = 1:length(app.UIAxes.Children.BrushData)
    app.UIAxes.Children.BrushData = uint8(zeros(size(app.UIAxes.Children.BrushData)));
    app.UIAxes.Children.BrushData(i)=1;
    pause(1)
end

After plot/scatterplot is created and assuming only one child for app.UIAxes, you could do the following:

app.UIAxes.Children.BrushData = uint8(zeros(size(app.UIAxes.Children.XData)))

Let's experiment:

for i = 1:length(app.UIAxes.Children.BrushData)
app.UIAxes.Children.BrushData = uint8(zeros(size(app.UIAxes.Children.XData)));
app.UIAxes.Children.BrushData(i)=1;
pause(1)
end

Answer 2

[RGB85]

The end user won't know the location of the data points to select. Essentially, there will be 3 buttons and 3 user-picked points of interest on the same UIAxes plot. The user can select a point, see the x,y coords in an edit field, and see the point visually on the plot. I want to include functionality for the user to be able to reset/repick each point if not satisfied with the first pick. Each button has the following code:

        function SelectPointButton_3Pushed(app, event)
            index = app.UIAxes1.Children.BrushData;
            xcoord = app.UIAxes1.Children.XData(logical(index));
            ycoord = app.UIAxes1.Children.YData(logical(index));
            
            app.x1EditField_2.Value = xcoord;
            app.y1EditField_2.Value = ycoord; 

            hold(app.UIAxes1,"on")
            plot(app.UIAxes1, app.x1EditField_2.Value,app.y1EditField_2.Value,"Color",'b','Marker','.','MarkerSize',15)             
        end

When I add the statement to zero BrushData, I'm getting the following errors:

app.UIAxes.Children.BrushData = uint8(zeros(size(app.UIAxes.Children.BrushData)));

Error using size

Dimension argument must be a positive integer scalar or a vector of positive integers.

Error in CalcCc/SelectPointButton_3Pushed (line 182)

app.UIAxes.Children.BrushData = uint8(zeros(size(app.UIAxes.Children.BrushData)));

Error while evaluating Button PrivateButtonPushedFcn.

I'm getting a similar error for "length" using the loop approach. If there's a way to reset all of the values in BrushData to 0, I think that would accomplish my goal. Is there any way I can just delete and/or reintialize brush data? I also tried clearing the whole axes,

cla(app.UIAxes);

and replotting everything. As BrushData is a child of UIAxes, I thought this would also clear BrushData, but it does not.

[Kevin Holly]

Your app.UIAxes probably has more than one child. This could cause that error when finding size(app.UIAxes.Children.BrushData)

try:

app.UIAxes.Children(1).BrushData = uint8(ones(size(app.UIAxes.Children(1).BrushData)))

I'm assuming your scatteplot/plot was the last thing added to app.UIAxes.

So, you could add a "Clear" button with a callback as such:

        % Button pushed function: ClearButton
        function ClearButtonPushed(app, event)
            app.UIAxes.Children(1).BrushData = uint8(zeros(size(app.UIAxes.Children(1).BrushData)));
        end        

Edit:

I decided to look at this again and noticed the above may not fix the problem as I see you are using a hold on after finding BrushData. You could save the brushdata as a property variable, so you don't have to keep track of the order of the children.

        properties (Access = public)
            index
        end

         function SelectPointButton_3Pushed(app, event)
            app.index = app.UIAxes1.Children.BrushData;
            xcoord = app.UIAxes1.Children.XData(logical(app.index));
            ycoord = app.UIAxes1.Children.YData(logical(app.index));
            
            app.x1EditField_2.Value = xcoord;
            app.y1EditField_2.Value = ycoord; 
            hold(app.UIAxes1,"on")
            plot(app.UIAxes1, app.x1EditField_2.Value,app.y1EditField_2.Value,"Color",'b','Marker','.','MarkerSize',15)             
        end

        % Button pushed function: ClearButton
        function ClearButtonPushed(app, event)
            app.index = uint8(zeros(size(app.index)));
        end        

[RGB85]

Apologies for the delay in response - I was on leave last week.

I've tried the making index a property and using the clear button, but I'm still getting the error:

Intermediate dot '.' indexing produced a comma-separated list with 2 values, but it must produce a single value when followed by subsequent indexing operations.

[Kevin Holly]

Please see the app attached. Let me know if this helps. I made the "select point" button, so the coordinates are not drawn until the user selects them after pressing the "Brush" button.

[RGB85]

I've integrated this approach into my code and it works. Thanks for all of your help!