Measuring Width & Height of Bounding Box

measurement

asked 2015-10-04 20:19:43 -0600

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I am a noob in OpenCV and i would like to use OpenCV to take some basic measurement of the object in photos and videos. I have read and tried a sample code about bounding box for contours, however I would like to modify it to measuring the value of the width and height of the bounding box.

Creating Bounding rotated boxes and ellipses for contours

I have read some posts here about this and the most obvious solution is to retrieve the 4 points of the bounding box, however how can i retrieve those variable in the code?

I have very little background in programming, so it would be appreciated if more detailed steps or codes are available. Thanks a lot.

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It is here

LBerger ( 2015-10-05 01:31:06 -0600 )edit

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answered 2015-10-05 05:55:51 -0600

StevenPuttemans

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updated 2015-10-05 06:00:13 -0600

This is actually quite straightforward, just use the getters from the Rect that defines the bounding box.

Code sample

// Make sure that the Rect is filled in any possible way
Rect test;
int x = test.x;
int y = test.y;
int width = test.width;
int height = test.height;
// Now with those parameters you can calculate the 4 points
Point top_left(x,y);
Point top_right(x+width,y);
Point bottom_left(x,y+height);
Point bottom_right(x+width,y+height);

For all of this keep in mind that OpenCV uses a coordinate system where y is pointing downwards and where the origin is in the top left corner of the image.

EDIT: this is offcourse for a standard Rect, if you want to apply to a RotatedRect, then use the functions in the link of @LBerger. A code sample can be.

RotatedRect test;
vector<Point> corners;
corners = test.points;
Point top_left = corners[0];
Point top_right = corners[1];
Point bottom_left = corners[2];
Point bottom_right = corners[3];