Author Topic: Using Image-J to quickly measure the area of a fin (or hydrofoil)  (Read 3928 times)

sflinux

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I thought Iíd share what seems to be a quick and easy way to measure the area of a fin.  This could just be easily be used the area of a hydrofoil.

Futures fins typically lists the dimensions of their fins in the specification section.  In that youíll find Area, Height, Base, & foil.  I find this very useful when comparing different fins.  But not all of my fins are futures.  How do you find the area of a fin that is not published? There are countless ways of measuring area.  But in the computer age, I wondered if there was an easy way to do this using a computer, that may actually be quicker. 

If you work with microscopes you may be familiar with a program called ImageJ.  In that program, you set a reference length, then you take a measurement.  Here is an example video:
https://www.youtube.com/watch?v=Qsxvnby7aCM
Available free here:
https://imagej.nih.gov/ij/download.html

To measure the area of a fin we need: a picture with a reference length.
To test this program, I took a picture of a fin on graph paper (10 squares/inch).
#If you have a printer, you can print your own graph paper, see https://print-graph-paper.com/
#note graph paper isnít necessary, just convenient.
I pre-measured the height of the fin, and the length of the base with a ruler.  I opened the picture in Image J. 
With the straight line tool, I drew from top of the fin to the base (base is where the fin meets the glass, ie. Top of fin box).

Analyze/Set Scale, I type in the known distance (height of fin).
With the straight line tool, I drew from the front of the fin to the back of the fin along the base.
Analyze/Measure: Look at the length of each measurement to see that it agrees with base length.
To measure the area, you select the freehand tool and trace the fin. 

Since my fin is on graph paper, I have reference for area.  I traced around blocks of 10 squares by 10 squares.  I used the zoom feature for this.
Analyze/Measure:  This gave me the area I was expecting, cool.
Next measure the area of the fin:
With the freehand tool, carefully trace around the perimeter of the fin. 
Analyze/Measure:  Look at the Area in the units of your measurement.  Mine was in the ballpark of what I was expecting compared to fins of known area.

Next I looked at an online picture of a Need Essential fin.  They only publish the height and base lengths, but do have a picture of the fin next to a scale (i.e ruler).  Can Image J be used to measure the area of a screenshot? 
https://www.needessentials.com/collections/accessories/products/8-single-fin
I took a screenshot of fin with the scale.  I opened the screenshot in image J.  With the straight line tool, I measured from the top of the fin to the base. 
Analyze/Set Scale, I enter in the known distance (height of fin).
With the straight line tool, I drew from front of the fin to the back of the fin along the base.
Analyze/Measure: Look at the length of each measurement to see that it agrees with base length.
Next I selected the freehand tool and traced the fin (donít include the area of the fin that is inside the fin box.
Analyze/Measure:  Look at the Area in the results measurement.  Again the measurement was in the ballpark of what I was expecting.

If you want to easily convert units, check out:
https://www.convertunits.com/from/sq+mm/to/square+inch

#At first I looked into programs like vector drawing programs like Inkscape.  Too complicated and takes too long.  Then I looked at CAD programs like Librecad, same problem. 

If you have an easy way of measuring area that you like to use, please feel free to share.  And happy new year.
« Last Edit: January 02, 2023, 12:15:02 AM by sflinux »
Quiver Shaped by: Joe Blair, Blane Chambers, Jimmy Lewis, Kirk McGinty, and Bob Pearson.
Me: 200#, 6'2"

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Re: Using Image-J to quickly measure the area of a fin (or hydrofoil)
« Reply #1 on: January 02, 2023, 03:19:50 AM »
Have you tried the polycam app?

sflinux

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Re: Using Image-J to quickly measure the area of a fin (or hydrofoil)
« Reply #2 on: January 02, 2023, 07:48:19 AM »
I have not used polycam, can the app measure area?
https://styly.cc/tips/nimi-lidar-polycam-3dscan/
The technology of LIDAR (iphone 12) and photogrammetry should be able to measure area, though I don't see a quick & easy way of doing it.
https://blog.fenstermaker.com/what-cell-phones-have-lidar/
https://www.blickfeld.com/blog/volume-monitoring-using-lidar/
https://www.igeeksblog.com/what-is-lidar-scanner/

Apps like polycam look super useful for getting a 3D model of shapes (wings, surfboards, etc), which would be super useful for 3D printing.  Thanks for sharing.

I used imageJ on a screenshot of a fin at FuturesFins.  I used the published lengths as the reference.  Using the technique mentioned above, I measured the area of the fin 3X and took the average, which is very close to the published measurement.  I am not interested in precision, just want the relative area of fins when comparing different shapes and sizes.
« Last Edit: January 02, 2023, 08:01:59 AM by sflinux »
Quiver Shaped by: Joe Blair, Blane Chambers, Jimmy Lewis, Kirk McGinty, and Bob Pearson.
Me: 200#, 6'2"

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Re: Using Image-J to quickly measure the area of a fin (or hydrofoil)
« Reply #3 on: January 02, 2023, 02:05:38 PM »
Have you tried https://www.finfoil.io ? I found it very useful for few projects.
in progress...

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Re: Using Image-J to quickly measure the area of a fin (or hydrofoil)
« Reply #4 on: January 02, 2023, 03:32:55 PM »
I have not used polycam, can the app measure area?

Only linear measurements in app, but you can bring the resulting file into any program that does. 

sflinux

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Re: Using Image-J to quickly measure the area of a fin (or hydrofoil)
« Reply #5 on: January 03, 2023, 12:04:55 PM »
Have you tried https://www.finfoil.io ? I found it very useful for few projects.
Finfoil.io works, thank you for the suggestion.  Finfoil.io is a very cool program for designing fins.
1) Select template
2) Select "+Camera" icon to load image to trace.  Click to drag image.
3) Fin Properties: Enter Depth
4) Edit the curve

I am a little slow on editing curves.  For that reason, J-image may be faster.  Both seem accurate.
Quiver Shaped by: Joe Blair, Blane Chambers, Jimmy Lewis, Kirk McGinty, and Bob Pearson.
Me: 200#, 6'2"

 


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