>>> 星瞳科技|OpenMV中国官方网站 <<<

>>> 星瞳科技店铺地址|OpenMV中国官方代理,全球九大代理商之一 <<<

>>> OpenMV3 Cam M7 官方高配版上市啦~戳我戳我戳我~ <<<

>>> 星瞳科技-OpenMV中文教程网 <<<

本节分享一下,如何通过摄像头里乒乓球的大小,计算摄像头与乒乓球之间的距离。

众所周知,乒乓球距离摄像头越远,摄像头里乒乓球的大小就越小,那么问题来了?
这个关系到底是什么呢?
(注:此处的数学几何问题,仅涉及到高中数学三角函数部分,不想看的,直接看结论也可)

为了简化问题,我们看一下图:

由左边的摄像头里的几何关系可得知:

所以有(1式)

由右边的真实环境里的几何关系得知:

带入(1式),可得(结论公式):

上面就是最终我们想知道的关系啦!
这是什么意思呢?
等号左边的Lm是长度,Bpix是摄像头中,球所占的像素(直径的像素)。等号右边呢,Rm是球真实的半径,Apix是是固定的像素,a是视角的一半。
所以!所以!所以!所以!所以!所以!所以!
这个公式告诉我们的就是:
实际长度和摄像头里的像素成反比
简化就是距离 = 一个常数/直径的像素

好啦,我们已经知道关系啦,而且还是这么的优雅简单!
具体操作步骤呢,就是先测出这个常数的值,怎么测不用说了吧,就是先让球距离摄像头10cm,打印出摄像头里直径的像素值,然后相乘,就得到了k的值!

然后 距离=这个常数/摄像头里像素点,so easy.

我这里贴出OpenMV的代码:

# Measure the distance
#
# This example shows off how to measure the distance through the size in imgage
# This example in particular looks for yellow pingpong ball.

import sensor, image, time

# For color tracking to work really well you should ideally be in a very, very,
# very, controlled enviroment where the lighting is constant...
yellow_threshold   = ( 56,   83,    5,   57,   63,   80)
# You may need to tweak the above settings for tracking green things...
# Select an area in the Framebuffer to copy the color settings.

sensor.reset() # Initialize the camera sensor.
sensor.set_pixformat(sensor.RGB565) # use RGB565.
sensor.set_framesize(sensor.QQVGA) # use QQVGA for speed.
sensor.skip_frames(10) # Let new settings take affect.
sensor.set_whitebal(False) # turn this off.
clock = time.clock() # Tracks FPS.

K=5000#the value should be measured

while(True):
    clock.tick() # Track elapsed milliseconds between snapshots().
    img = sensor.snapshot() # Take a picture and return the image.

    blobs = img.find_blobs([yellow_threshold])
    if len(blobs) == 1:
        # Draw a rect around the blob.
        b = blobs[0]
        img.draw_rectangle(b[0:4]) # rect
        img.draw_cross(b[5], b[6]) # cx, cy
        Lm = (b[2]+b[3])/2
        length = K/Lm
        print(length)

    #print(clock.fps()) # Note: Your OpenMV Cam runs about half as fast while
    # connected to your computer. The FPS should increase once disconnected.

成果是这样的,通过串口把距离打印出来。