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Tracing Image scale jump at 0.1 ?

Discussion in 'Using Alibre Design' started by MKR, Oct 21, 2020.

  1. MKR

    MKR Member

    Hi all

    I'm testing "Tracing Image" out, but the scaling is too rough. It jumps by 0.1 even when I use "Calibrate Size". In my case it gives an error of 15 mm. Is there a setting that can give me 3 decimals in the scaling?

    /Michael
     
  2. NateLiqGrav

    NateLiqGrav Alibre Super User

    Does it work with the decimal places set for the part units?
     
  3. MKR

    MKR Member

    In 2D Sketch i got 3 decimal places.

    I had to scale the image to 10% to get an acceptable accuracy. But it gives a very rough picture to trace after.



    scale.jpg decimal.jpg
     
  4. MilesH

    MilesH Alibre Super User

    Using the tracing method in Drawing workspace, you can enter any ratio you need. Are you saying that, using the new feature, if you manually enter any multiplying factor it gets rounded up????
     
  5. DavidJ

    DavidJ Alibre Super User Staff Member

    I've just done an experiment with 2 instances of the same image, on the same plane. One scaled 0.94, one scaled 0.87; both get rounded to 0.9 in the dialogue after entry - but the 2 images are of different size on screen - so this seems to be an issue with displayed precision in the dialogue. Does that fit other's experience?
     
  6. MKR

    MKR Member

    It rounds up / down to the nearest 0.1 in both cases.
     
  7. MilesH

    MilesH Alibre Super User

    Thanks David.

    The important thing is to be able to enter the exact scaling ratio you want, even if it's 0.000094.... If you're tracing an image of an object with a length of 2.5 meters and you're multiplication factor entry is limited to two decimal places, that would only be accurate to the nearest inch! Could you confirm that you can enter a multiplication factor to at least six decimal places and that the scaling reflects this? Whatever rounding up gets displayed in the dialogue afterwards......
    Thanks
     
  8. DavidJ

    DavidJ Alibre Super User Staff Member

    I can enter a 6DP value - not easy to be sure whether that is respected in the actual scaling.

    You can type more than 6DP into the Calibrate Size dimension box.
     
  9. MilesH

    MilesH Alibre Super User

    Thanks David.

    I've attached a 7,000 pixel long image if anyone wants to check. The overall length of the object of the object is 2250 mm so that's what a line traced over it needs to dimension to. Hi Res F5.6 Compressed.jpg
     
  10. DavidJ

    DavidJ Alibre Super User Staff Member

    So - surely use the Calibre Size button and type in 2250mm ?
     
  11. MilesH

    MilesH Alibre Super User

    I don't have the update so, I've no idea how Calibrate works... MKR said in the first post that "It jumps by 0.1 even when I use "Calibrate Size". In my case it gives an error of 15 mm." I expect that the scaling will respect the entered value exactly but I need to be certain about this before I update ;-)
     
  12. DavidJ

    DavidJ Alibre Super User Staff Member

    Miles - I used calibrate size with 2250mm. I then sketched a rectangle trying to match the length of the drawing - extruded it an measured the edge 2250.067mm reported length.

    When zoomed in on the ends of the image, the lines really aren't that sharply defined, and that's likely to be the limitation - both in doing the calibration and in any subsequent tracing. I think users need to be realistic about the potential accuracy of any technique based on images.
     
  13. MilesH

    MilesH Alibre Super User

    Great. That seems to work fine. Does Calibrate work by you choosing 2 points on the image and then entering a value for their distance?

    The drawing is an ink drawing photographed from a distance of 9 metres. That's why it's a bit "fuzzy" :)
     
  14. simonb65

    simonb65 Alibre Super User

    Yes, that's how the scaling works, but it doesn't currently rotate that 'datum' line to a specific angle, you have to guess and enter the rotation manually. That bit is a bit hit and miss at the moment!
     
  15. MilesH

    MilesH Alibre Super User

    Ok. Understood. Thanks Simon.
     
  16. DavidJ

    DavidJ Alibre Super User Staff Member

    Just did another experiment, rotated Miles image by 45 degrees then used calibrate - the Calibrate option copes with the angle of the line (presumably applying necessary uniform scale to get the linear value provided).
     
  17. GIOV

    GIOV Alibre Super User

  18. MilesH

    MilesH Alibre Super User

    From the thread GIOV linked:
    The fact that is not a stored value is good because it means, presumably, that you can tweak the X Y scale ratio after using Calibrate. This is often necessary with images scanned through rollers (Y scale gets stretched).
     
  19. MilesH

    MilesH Alibre Super User

    Great. That makes sense.
     

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