Suggestion to improve needle-camera offset calibration

[mrandt]

I like the way Reeza implemented the "Backoff" calibration using a sheet of paper for reference!

This triggered an idea in me which could help to improve and ease needle-camera offset calibration:

Remember carbon paper - used to create copies when using mechanical typewriters or handwriting? It can still be bought

1. Put piece of carbon paper on table - black side to table surface, maybe a piece of paper underneath it.
2. Probe down needle, this will leave a clearly defined black mark on table or paper
3. Position camera overhead the mark - either manually jogging it there or by using optical detection algorithms (software feature?)

Probably much more accurate than trying to position the needle exactly over a known feature...

If carbon paper is not available, you could also use a pencil to "blacken" a piece of paper - just tried it and the mark is nicely visible on my table surface.

[JuKu]

Good idea, I added that to instructions. Thank you!

[mawa]

Besides programming and electronics I also do some airbrush art.

To prepare my motives I use a pit black aerosol transfer spray called "GHIANT Transfer Spray". Price was € 10.65.
You usually spray the back of a printed photo to transfer the contours to your spray cardboard paper.

That spray really gives you a "tasty" black carbon paper, which really gives good calk results.

Here is my result (zoomed image):

2015-07-11 20_47_44-LitePlacer 2015.png (576.67 KiB) Viewed 2567 times