hello (stef) -
 
is it ok if i don't set up the worldspace? I've got a model that I will re-orient in my cad program later, and i'm wondering how it affects my calibrated space if i don't set up the axes. I've done my reference calibration, and measurements taken elsewhere in the model are reasonably accurate.
 
thanks

Hello mcah,
 
  It's not necessary to set up "your" worldspace, because the calibration is setting one for you automatically. IM chooses a "good" set of locators when calibrating, depending on their location in 3D(not co-planar), their distribution, ...etc...
 It might change over different calibration, if adding new locators, or if moving some locators ...  
If you set yours, it will stay persistent over calibration.
 
Best,
 
Stef

Hi Stef -
 
so if I understand correctly, IM doesn't see the worldspace as a set of constraints - it just orients the data. I was worried that IM used the right-angle info from the worldspace setup to make the calibration more accurate.
 
Another question: I've successfully calibrated a 3d space using only two images, and IM correctly and easily finds points in both images with good accuracy. However my test measurements made from the images indicate that the space is not in fact well calibrated - when i measure a roof, for example, that has constant width in reality, IM tells me that it gets narrower as i recede in space. Any way to deal with this? It would be cool to have not only a right angle constraint but also a parrallel line constraint, to help IM with situations like this.

Hello,
 
  Yes, the worlspace is not a constraint for the calibration.
 
2 images case: If you have only 2 images to calibrate, it is welcome to know a little bit more about your shots or scene:
- focal constant is recommended
or  
- focal known if possible
or
- adding a constraint (corner is the strongest contraint)
 
The best is knowing the internal params of your camera (focal, distortion) from a previous "good" calibration. I did that by calibrating 2 grids in different planes ...
 
Best,
 
Stef

Hi Stef -
 
thanks for the suggestions - can you tell me more about this grid calibration system? I'd like to do it, because I'm not getting the results I would want from 2 images. I'm wondering if I should use the PanoTools plugin called lensfix to correct for the distortion of my lens before putting the image into IM. Another question: I'm assuming that if my lens is a 15mm lens, but shot with a D100 (1.5x focal length factor) I should tell IM that the lens is 22.5 mm, right?
thanks
andrew