Issue with calibrating photo canvas

[bmartinek]

Looking for some suggestions. I'm trying to model the underside interface for this bike saddle and took 3 images to capture and made sure to try and take them dead on as possible. Then I went to calibrate the first one and matched the other images to it visually. when I was working on the back I noticed the dimensions were way off the real item. So I went to the side and rear and they are just way too small, but they dimensions are accurate. Any suggestions. I mean the bottom and side view should match in overall length for sure. A bit confused:

Attaching file as it's a bit hard to see I think

[jeff_strater]

@bmartinek - I think the problem is that the "Seat back" canvas is too small.  I think the points indicated by the arrows here should match up and they don't:

[bmartinek]

Hi @jeff_strater , thanks for the reply, but this is the crux of the issue. I did have it scaled to match the first image like this:

Then I went to calibrate it and I get this:

Much smaller than the image in the horizontal plane. Both images have the same 72 DPI. 

Is there a way to correct this so I can model the curvature and cutouts accurately? 

[davebYYPCU]

72 dots per inch????  How do you know what size any part of this file is?

Your 3 canvass have no common size evident.

Your model has no Dimensions, so I am unable to help, even to start from scratch.

First step with canvass is to import it, then right click that canvass in the browser and select Calibrate, 

Any source size is lost when imported, so has to be done by Fusion - real early,

then pick two points on the graphic, and add the dimension of the real world item, 

Example  load the back view, and on the picture, dimension the widest part, same as the real world part.

Step 2, the Canvass will no longer relate to the File Origin, so you Right click the Canvas and Select Edit, and position the canvass onto the Origin where it makes the most sense.

Might help.....

[Anonymous]

What points on the saddle are you using to calibrate? I don't fully understand your problem but here are some things to know about using using photo canvases:

• dpi has no relation to the object size, that's why you need to calibrate a canvas at the start. 
• Always start by calibrating the canvas. If you need to move the image relative to a sketch or something just move them around in the timeline. 
• perspective is a thing so any sketch to be somewhat dimensionally accurate needs to be on the same plane that calibration was done on. And that plane needs to be perpendicular to a line from the camera lens to the object. 
• Even if you control for perspective perfectly a camera image still has curvilinear perspective because the plane is actually more like a section of a sphere flattened. This means things will still be a little off the further you go from the center of the image. 
• You can reduce the perspective if you take the image as far away from the object as possible and zoom in. 

[jeff_strater]

see the screencast below (just a link, then I'll re-post it embedded).  I show how I would go about both calibrating and aligning these 3 images.  Of course, you would use the real measurements of the seat length, but I just rounded to a value of 230.  Here is the basic flow I used:

1. calibrate the top/bottom view length to 230mm (seat front to back)
2. calibrate the side view to the same length (again front to back)
3. edit the side view position so that the front and back points are aligned
4. go back to the top/bottom view, and use calibrate again, just to measure the seat width (don't change it)
5. calibrate the back view so that the width matches what is measured in #4

at this point, the canvases are all approximately the right size and position.  You would want to do this more carefully in a real workflow.

screencast:  https://knowledge.autodesk.com/community/screencast/bf0b5b9a-eaff-42b9-986d-edc16a1d0795 

[bmartinek]

This was helpful. in all the examples for canvas calibration I've never seen it done in two dimensions. The Seat bottom and top now work correctly together. I will still need to work with the rear which has been more difficult and the dimensions still don't seem to line up. Will experiment. Thanks for the assist.