Hi,

This is my first using Inkspace and posting in the forum. So if I am doing it anything wrong or posting in a wrong place kindly let me know.
For last few days I searched the internet extensively on this subject both with Inkspace and GIMP.

What I want to get done with inkspace is to input an image with an airfoil and get the cordinates of it.
The steps I thought of using to get it done is as follows

1. Import Bitmap or JPG image of an airfoil.
ex:
http://2.bp.blogspot.com/_NN-IjvHwReE/S ... F-1015.png
https://karoliinasalminen.wordpress.com ... y/nlf1015/

2. Then use a tool like "Trace bitmap" or "Trace pixel art" tool to convert it to a vector image
(I did it because I think it will increase the accuracy of the final result)

3. Get the cordinates of the path of this vector image to a text file.

What I tried so far

1. Tried to get cordinates from the SVG file directly. But this automatic path creation seems to make the curve so complicated. So there are many paths with many different curves. Its almost a nightmare to make all these curves back by myself to get like 120 points. As a side note I am going to redraw the path from the cordinates with a quadratic spline once I get the cordinates.

2. viewtopic.php?f=5&t=8826

With the image file given on top of this message I used this extension but what I got is this.

21.180939,-8.5597531
5.862105,-18.021749
94.305939,-37.728471
176.98413,-23.550893
180.30747,-16.224081
151.84795,-14.278358
64.930939,-8.0539281
21.180939,-8.5597531
21.180939,-8.5597531

Including handles:
21.180939,-8.5597531 21.180939,-8.5597531 2.571118,-11.181624
0.38447263,-12.532252 5.862105,-18.021749 16.890206,-29.07374
55.87558,-37.760314 94.305939,-37.728471 123.61092,-37.704191
149.28658,-33.301353 176.98413,-23.550893 196.21001,-16.782739
196.43725,-16.281747 180.30747,-16.224081 172.6083,-16.196551
159.80151,-15.320979 151.84795,-14.278358 116.97331,-9.7066921
100.04843,-8.4946421 64.930939,-8.0539281 44.649689,-7.7994061
24.962189,-8.0270281 21.180939,-8.5597531 21.180939,-8.5597531
21.180939,-8.5597531 21.180939,-8.5597531 21.180939,-8.5597531

I am not sure how can I get X-Y cordinates from this.

Is there anyway to get what I discribed above done in an easy doable way ?
What I thinking doing is to get the XY cordinates from the object shown in the screan directly itself if there is any possible method of extracting it.

Can you kindly let me know whether any posibiliy for this ..?

Thanks so much

Welcome aboard!

You seem to have a good search, yet I'm not entirely sure how would that be beneficial in a later design stage.
Using the trace bitmap can be fast, but may not result in the best node placement.

Bézier curves are like parabolas, thus making a circular arc perfect is not possible.
For a manual tracing I would put nodes wherever the curvature changes notably, and pull handles about 1/3 of the segment -making it sure that the overall turn is less than 90°.

How to go on when you have a nice vector shape?
Using coordinates like 2,571118 is painful manually.
If you need this for a cad program, exporting to dxf, or, importing the svg there wouldn't be possible?
If you need this to reproduce the shape, why can't you import the exact path?

Problem with the coordinates is that inkscape -and the svg specs suggests for that matter- use a viewbox to scale the drawing to real world units, and keeping all the other stored information in pixels -meaning those coordinates you see in the xml editor may not be what you are after.

There are extensions to visualize path. With that, handles can be plotted.
There is another one too, that numbers nodes.
If they don't work for you, I'm guessing it wouldn't take too much editing a new extension from those two that can plot the coordinates.
(Even though I'm not sure how to deal with the real world units or making a correct code myself.)

Hi.

Your extracted coordinates are what you want,
what you got is x and y coordinates for an airfoil Excellent research!

If you look at the list of coordinates you will see some duplicates - the last two lines are the same as the first.
Depending on what you want to use the coordinates for you can remove the last line in a text editor before you "process" the file any further.
(To make a closed curve you want the first and last set of coordinates to be the same.)

If you just want to plot the shape you can use Veusz - an excellent program for plotting.

To get a smoother curve when importing into another application (CAD program) you can increase the number of coordinates in inkscape by
selecting your shape -
Press F2 - to get into node edit mode
Select All Nodes - Ctrl A -
Inssert Nodes - by clicking on the Plus Sign Icon in the upper corner of the main inkscape window or use the plus key on the numerical keypad.

A better and more accurate approach (Pun Intended) for plotting your airfoil is to figure out the profile by studying the aircraft spec, most use one of the NACA airfoils.
You can find coordinates for most (all?) NACA airfoils on the net:
http://m-selig.ae.illinois.edu/ads/coord_database.html

You can also create your own:
http://airfoiltools.com/

Please post images of your "finished product" here!!

Hi,

Thanks so much for your help and sorry for the late reply

I am working on modifiying the extention. The suggestion you gave really helped me to increase the number of points resulting greater accuracy.
At this moment I am stuck with XFLR5.

The dat file I got works in XFOIL but not in XFLR5. I will find the result and link the final result soon.

Thanks again.