[200 opencv routines] 216 Draw polylines and polygons

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【youcans Of OpenCV routine 200 piece 】216. Draw polylines and polygons

function cv.polylines() Used to draw polygonal curves or polylines .
function cv.fillPoly() Used to draw one or more filled polygon areas .
function cv.fillConvexPoly() Used to draw a filled convex polygon .

The function prototype ：

cv.polylines(img, pts, isClosed, color[, thickness=1, lineType=LINE_8, shift=0]) → img
cv.fillPoly(img, pts, color[, lineType=LINE_8, shift=0, offset=Point()]) → img
cv.fillConvexPoly(img, points, color[, lineType=LINE_8, shift=0]) → img

Parameter description ：

• img： Input / output image , Allows single channel grayscale images or multi-channel color images
• pts： Polygon vertex coordinates , A two-dimensional Numpy List of arrays
• points： Polygon vertex coordinates , A two-dimensional Numpy Array
• isClosed： Closing sign ,True Represents a closed polygon ,False Indicates that the polygon is not closed

matters needing attention ：

1. Pay special attention to polygon vertex coordinates pts The format of ：
   pts It's a list , The elements in the list are two-dimensional Numpy Array , Each element represents a set of vertex coordinates .
   A two-dimensional Numpy The shape of the array is (m,2), Each row represents the coordinates of a vertex of the polygon (xi,yi), The data format should be integer .

   for example ：

   points1 = np.array([[200,100], [295,169], [259,281], [141,281], [105,169]], np.int)
   points2 = np.array([[200,400], [259,581], [105,469], [295,469], [141,581]])
   

   points1、points2 It's in the shape of (m,2) Two dimensions of Numpy Array .
   For the function cv.fillConvexPoly, Use 2D Numpy Array points1 or points2 As a parameter .
   For the function cv.polylines And cv.fillPoly, You can't directly put two dimensions Numpy Array points1 or points2 As a function parameter , Instead, use it as an element of the list , Such as ： [points1]、[points2] or [points1, points2].

2. function cv.polylines And cv.fillPoly You can draw or fill one or more polygons .
   When the list pts There is only one element in , It's a two-dimensional Numpy Array time , Draw a polygon ;
   When the list pts There are multiple elements in , That is, multiple two-dimensional Numpy Array time , Draw multiple polygons , Each two-dimensional Numpy The vertex coordinates in the array are treated as a polygon .

3. The closing sign is True Draw a closed polygon , The line segment from the last vertex to the first vertex will be drawn ; The closing sign is False Draw a non closed polyline , There is no connection between the last vertex and the first vertex .

4. function cv.fillPoly And cv.fillConvexPoly You can draw filled polygons .
   cv.fillConvexPoly Running speed ratio of cv.fillPoly Much faster , Especially suitable for filling convex polygons , Often used for contour processing .

5. function cv.fillConvexPoly It can not only fill convex polygons , You can also fill any monotonic polygon that does not intersect itself , That is, the polygon whose contour intersects each horizontal line at most twice （ Although its top and / Or the bottom edge may be horizontal ）.
   This sentence comes from the official document , The contents in brackets “ Top and / Or the bottom edge may be horizontal ” Not easy to understand , You can combine routines 4.7 The bottom right figure understands . The author suggests that in addition to contour processing , Try not to use cv.fillConvexPoly To fill non convex polygons .

routine A4.7： Draw polylines and polygons

   # A4.7  Draw polylines and polygons 
    img = np.ones((980, 400, 3), np.uint8)*224
    img1 = img.copy()
    img2 = img.copy()
    img3 = img.copy()
    img4 = img.copy()

    #  Polygon vertices 
    points1 = np.array([[200,100], [295,169], [259,281], [141,281], [105,169]], np.int)
    points2 = np.array([[200,400], [259,581], [105,469], [295,469], [141,581]])  # (5,2)
    points3 = np.array([[200,700], [222,769], [295,769], [236,812], [259,881],
                     [200,838], [141,881], [164,812], [105,769], [178,769]])
    print(points1.shape, points2.shape, points3.shape)  # (5, 2) (5, 2) (10, 2)

    #  Draw polygon , Closed curve 
    pts1 = [points1]  # pts1  Is a list of , The shape of the list element is  (m,2)  Of  numpy  Two dimensional array 
    cv.polylines(img1, pts1, True, (0,0,255))  # pts1  Is a list of 
    cv.polylines(img1, [points2, points3], 1, 255, 2)  #  You can draw multiple polygons 

    #  Draw a polyline , The curve is not closed 
    cv.polylines(img2, [points1], False, (0,0,255))
    cv.polylines(img2, [points2, points3], 0, 255, 2)  #  You can draw multiple polylines 

    #  Draw filled polygons , Pay attention to the treatment of overlapping parts 
    cv.fillPoly(img3, [points1], (0,0,255))
    cv.fillPoly(img3, [points2, points3], 255)  #  You can draw multiple filled polygons 

    #  Draw a filled polygon , Pay attention to the overlapping part 
    cv.fillConvexPoly(img4, points1, (0,0,255))
    cv.fillConvexPoly(img4, points2, 255)  #  You cannot draw polygons that have self intersections 
    cv.fillConvexPoly(img4, points3, 255)  #  You can draw concave polygons , But be careful with 

    plt.figure(figsize=(9, 6))
    plt.subplot(141), plt.title("closed polygon"), plt.axis('off')
    plt.imshow(cv.cvtColor(img1, cv.COLOR_BGR2RGB))
    plt.subplot(142), plt.title("unclosed polygo"), plt.axis('off')
    plt.imshow(cv.cvtColor(img2, cv.COLOR_BGR2RGB))
    plt.subplot(143), plt.title("fillPoly"), plt.axis('off')
    plt.imshow(cv.cvtColor(img3, cv.COLOR_BGR2RGB))
    plt.subplot(144), plt.title("fillConvexPoly"), plt.axis('off')
    plt.imshow(cv.cvtColor(img4, cv.COLOR_BGR2RGB))
    plt.tight_layout()
    plt.show()

【 At the end of this section 】

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[email protected] Original works , Reprint must be marked with the original link ：(https://blog.csdn.net/youcans/article/details/125468148)
Copyright 2022 youcans, XUPT
Crated：2022-6-26
Welcome to your attention 『youcans Of OpenCV routine 200 piece 』 series , Ongoing update
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210. There are so many holes in drawing a straight line ？
211. Draw vertical rectangle
212. Draw a slanted rectangle
213. Draw a circle
214. Detailed explanation of parameters for drawing ellipse
215. Draw approximate ellipses based on polylines
216. Draw polylines and polygons