How to detect water edges, and measure length

I’m trying to measure the length of the water sheet and droplet size when two laminar flows are impinged.

The shape formed keeps changing with a change in velocity, and angle of the flow. I want to measure the distance centre orange line, and the yellow lines on both sides. The starting point will be fixed to the place where the two flows collide.

The process I’m following is:
Step 1. To detect the edges and manually select the starting point.

Step 2. Find the endpoint and measure the distance in pixels and later convert it to desired units.

I’m not sure how to do step 2. And also if this is the best approach to do this to find droplet size?

Can someone please suggest what would be the best approach to achieve this?

related: opencv - How to detect water edges from a flow and measure length - Stack Overflow

I does not know the aim of this work, but be aware, you are facing to 3D flow.
Also, your experience must be done in static or dynamic mode ? I think you need to give more details.

For image processing, common algorithm used :

  • to put a black background.
  • apply binary transformation of your image with a threshold value
  • apply findcontours processing
  • iterate in the output list result, & calculate area