Best practice for collecting measurements

I am creating a reference website for professional cornhole bags. My goal is to create a central location to compare standardized measurements between the bags.

I am hoping to use Fiji/ImageJ to measure the horizontal and vertical widths and the radius of the corners but I wanted to ensure I am using the most reproducible and accurate methods. I am taking three measurements of each variable and want to make sure they are consistently taken the same way. My thoughts were to take width measurements every 1/3 of the max. I am stuck trying to figure out how to consistently measure the radius of the corner. I am open to suggestions too. Thank you for taking your time to read this.

If you have any questions, please let me know and I will answer as soon as possible.

Could you elaborate on how you are trying to take these measurements? You say “every 1/3 the max”. What does that mean? Are you looking for an automated way to do this or are you fine with measuring the length of drawn lines? How are you calculating the bag dimensions from the measurements?

I would ultimately love something that could automatically do it to reduce human error.

The bag is about six inches by six inches square with rounded corners. I want to take a maximum measurement of the horizontal and vertical widths. I was thinking about get the X and Y coordinates of the first instance where it starts measuring from to the max X and Y coordinates. Divide the difference by four and then take three measurement every from the first instance. This would give me three measurements from the main portion of the square.

I am fine with taking the length of drawn lines. It would be the same as me measuring it with a ruler.

I saw that you can calibrate the image (Fiji/ImageJ) with a known distance in the picture. I was going to use a digital caliper so that I know the exact distance (+- some amount) on the image. Once calibrated, I could apply that to all the measurements taken.

I plan on taking the pictures from the same height using a tripod.

I hope that is clear, but please ask more clarifying questions as needed.

Again, thank you for taking your time to help in this.

I see. Well, if you are okay with measuring drawn lines, then here is a quick idea on how to get a rough estimate of the radius. Draw a straight line along one side of the bag and allow it to extend beyond the corner you are trying to measure. Do the same with the other side that contributes to the corner. Mark (using the points) the intersection of the two lines as well as where they appear to start diverging from the edges of the bag. Measure the distance between those points.

I did a mock up of your suggestions (I think). I wasn’t able to find a way to draw an arc but I beat fit a circle to the square. Is there a way to automate the box being drawn with - circle in each corner?

Unfortunately, I don’t. Would the corners be more or less the same radii or could some bags have intentionally different corners? If the former, there might be a way to semi-automate the process using auto-thresholding to identify the bag and the bounding rectangle.

Sadly, the radii vary quite drastically on each and between bags.

What would you recommend doing to determine the auto-threshold? That might be a good first step to determine the next step. All bags fall within a specific size range (6 in by 6 in). Would that help?

I found a potential method for making the bounding box that rotates to the orientation of the bag (if tilted). I did have to take a new picture using a white backdrop to create more contrast in the image. I used this image and in ImageJ conducted the following:

  1. Made the image 8-bit
  2. Used the threshold to make it black and white.
  3. Created Selection
  4. Run a Macro to create a tilted bounding box

I am trying to figure out how to get the measurements of those lines that create the box, and then I’ll be able to make some circles for the radii of the corners.

Again, I am not sure this is the easiest method to do this but I hope I get something quicker figured out.

Thank you.

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  1. Made the image 8-bit
  2. Used the threshold to make it black and white.
  3. Created Selection
    Then you do: fitRectangle ->Analyze-> Measure
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Thank you for that suggestion. It works as well. I found that the difference in measuring the tilted rectangle and straightened rectangle differ very little. I believe this is a great option for me.

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