MATLAB: How does getPosition work in impoly

Image Processing Toolboximpoly

Hello,

i've been using impoly for drawing polygon in a blank figure, and then use the pos=getPosition(h) function to get the position of the drawn polygon. but the problem is, when i changed the corner of the drawn polygon, the "h=getPosition" function won't retrieve (update) the new position, is there a way to update the position while we change the corner?.

also, suppose that i draw a few polygon in a figure using only "h=impoly" then i want to delete one of the previous polygons (by choosing one of the drawn polygons to be deleted). i have used the "delete(h)" command but only the previous body that can be deleted.

thanks in advance 🙂

Best Answer

I'm not seeing the behavior you observe. You wrote the "h=getPosition" function, so I'm wondering if you're overwriting your h variable (so it no longer refers to the impoly object)? Or maybe that you have multiple ones (given your second question) and you're changing one, but that's not the one your h variable refers to.

Anyway, to address both questions:

imshow('street1.jpg')
h(1) = impoly(gca,[20,20;80,20;80,80;20,80])
h(2) = impoly(gca,[200,200;280,200;280,280;200,280]);
x1 = getPosition(h(1))
%  Move one of the corners of the first polygon
x2 = getPosition(h(1))
x1 - x2

Note that h is a 2-element impoly object (1 element per shape). x1 and x2 are numeric arrays of the coordinates.

EDIT TO ADD: OK, didn't understand the (first) question at all, sorry! The answer to the second part stands: just make h an array of impoly objects (or, of course, just have multiple objects with different variable names, but that's harder to maintain).

For the first part, about updating xy whenever you move a vertex, how about this:

addNewPositionCallback(h(1),@(p) assignin('base','xy',p));

This is dangerous, in that you are clobbering anything in the base workspace with the name xy. And if you want this in a function, then don't use the base workspace.

Also, I just realized I didn't fully answer the second part, about deleting. The point I was making was that if you keep all the handles in an array, you can delete any of them:

delete(h(1))

Related Solutions

MATLAB: Editing impoly polygons in a GUIDE app

"after this function has executed, I don't see any way to get to that polygon again to detect changes"

Once the callback function is finished, all variable values within the function are lost forever unless you save them (exceptions are global and persistant variables which are not recommended).

You can use guidata() to save variables to your GUI so when you enter a callback function, those values can be retreived. Here's a demo that stores/retreives data in/from the GUI figure itself but you could chose any GUI object.

function myCallbackFunction(hObject, event, handles)
h = impoly(. . .); 
dat = guidata(handles.figure); %assuming the handle to your figure is named 'figure' 
if ~isfield(dat,'PolyHandles')
    % add the field if it doesn't exist already
    dat.PolyHandles = []; 
end
dat.PolyHandles(end+1) = h; %add new handle to end
guidata(handles.figure,dat); %store the updated data 
end

To clear the handles,

dat = guidata(handles.figure); 
dat.PolyHandles = []; 
guidata(handles.figure,dat);

Once you have the handles, you can do everything in your question: edit them, copy them to another image, etc.

MATLAB: How to extract the ROI using impoly

Hi,

You should use either imcrop, or impoly.

Using imcrop, you can select a rectangular region of interset. By the way, there is also a syntax "IMG2 = imcrop(IMG);". You can use like this:

   grayImage = imread('pout.tif');
   figure, imshow(grayImage);
   img2 = imcrop;
   imshow(img2)

Using impoly, you can select a polygonal region of interest. This polygon can be represented as an ordered list of vertex coordinates. You can then convert this polygon into a binary mask by using "roipoly" function.

regards, David

Best Answer

Related Solutions

MATLAB: Editing impoly polygons in a GUIDE app

MATLAB: How to extract the ROI using impoly

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