## >>> 星瞳科技-OpenMV中文教程网 <<<

（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）

实际长度和摄像头里的像素成反比

# 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.