Basic Shape Detection from an Image

Code Flow Overview:

Step 1: Include all neccessary libraries and read the image. 

Step 2: Convert the image into grayscale to simplify the shape detection process. 

Step 3: Contour Processing
    3a: Draw contours and find out the number of contours draw for each shape. 
    3b: Calculate the centroid in order place the text appropriately. 

Step 4: Identification of the shape 
    4a: TRIANGLE IDENTIFICATION
        -- Triangles have three vertice; if the approximation has three vertices it's likely a triangle. 
    
    4b: SQUARE & RECTANGLE IDENTIFICATION
        -- Both squares and rectangles have four vertices. 
        -- Calculated based on their aspect ratio 
        -- If aspect ratio is close to 1, it is considered a square; else it is considered as a rectangle, 

    4c: TRAPEZIUM IDENTIFICATION
        -- Trapeziums have four vertices. 
        -- Trapeziums are neither a square nor a rectangle but has nearly equal opposite sides. 
        -- Calculated by comparing the length of the opposite sides. 
        -- If opposite sides are not of equal length then it is a trapezium. 
    
    4d: PENTAGON IDENTIFICATION
        -- Pentagons have five vertices. 
        -- If approximation has five vertices, it is then identified as a pentagon. 
    
    4e: HEXAGON IDENTIFICATION
        -- Hexagons have six vertices. 
        -- If the approximation have six vertices, it is then identified as a hexagon. 

    4f: OCTAGON IDENTIFICATION
        -- Identified basis the side lengths using the Euclidean's distance.
        -- Length of the side is computed via the Euclidean Distance between the consecutive vertices. 
        -- If all the side lengths are roughly equal the shape is considered as an octagon. 
        -- If not, then it is considered as a rectangle (Use Case: Rectangles with curved surface edges).
        -- If the absolute difference between any side length and the first length exceeds the threshold, then it is a rectangle. 
        -- If it does not exceed the limit then it is an octagon. 

    4g: CIRCLE & ELLIPSE IDENTIFICATION
        -- Circles and ellipses are calculated basis their aspect ratio. 
        -- If the ratio of the minimum to maximum diameter is very close to 1, it is considered as a circle. 
        -- If the ratio is not close to 1, it is then called as an ellipse. 

Step 4: Displaying the result over the annotated shapes. 

NOTE: Input image file can be accessed via the include folder.