Best practice for implementing PTGui panoramas in 3ds max for camera matching?

[Peter Letten]

Hi All,

It'd be mightily appreciated if anyone can point me to a resource regarding implementing PTGui panoramas in 3ds max for camera matching

To provide a little more detail:
I have years of experience creating verifiably accurate 'single frame' montages for visual impact assessment. Increasingly however clients are requesting 180' pano montages.
To date I've created these from a series of individual photomontages then photo stitched into a panorama as a last step. (While I imagine this is the most accurate method, its certainly not the most efficient, and therefore gets expensive for the clients).

A much more elegant solution is to render a single spherical panorama to 180' and camera match that to a projection from  PTGui   .
However, this is throwing up a number of concerns/queries. (I've spent a good few hours on this forum and others. While some of my queries below are answered in part, I feel there has to be a more comprehensive resource out there somewhere).
Queries include:

• Panorama editor - How accurate is the FOV value under cylindrical projection? I imagine there'd be quite a range here depending on the shoot lens/camera/tripod type. From my test file it seems to be out by a good 10-20'... could this be right?
• Panorama editor - it's possible to tilt/shift/bend the projection of the panorama, which is great. But can you do it with a reference image overlaid on top? Currently, I've been doing some trial and error to incrementally tweak the panorama projection until it matches in photoshop my rendered reference points (surveyed points and Lidar data which I know to be true)
• What image aspect ratio and camera type to be using in 3d to best match the panorama (from scouring forums and doing some testing I'm currently using Warped-spherical (old style) and image aspect ratio of 4:1 to match my override settings of FOV 180, and cylinder height of 45.
• How to align the camera in the first place using cylindrical projection. My current workflow is to locate the camera by performing a camera match to a couple of the original single frame images, and the render the cylindrical projection from that point. I've seen posts in 3d forums with people using a spherical environment projection, has anyone had any success using this for cam alignment?

I have more Q's, but as mentioned, I suspect there already exists a well developed thread/resource regarding this topic. If only I could find it!
Any input would be very much appreciated.
Thanks in advance

[PTGui Support]

Hi Peter,

> * Panorama editor - How accurate is the FOV value under cylindrical

> projection? I imagine there'd be quite a range here depending on the
> shoot lens/camera/tripod type. From my test file it seems to be out
> by a good 10-20'... could this be right?

If you're shooting a 360 degree panorama then the field of view will be
very accurate. A 360 degree panorama wraps around at the left and right
hand edge. If PTGui wouldn't correctly estimate the field of view of the
source images, the panorama would not meet at the ends.

For non-360 degree images this is not the case. If you let PTGui
optimize the lens focal length (see the optimizer tab), it can deviate
somewhat from the actual value. In that case it would be best to enter
the focal length of the lens in the Lens Settings tab, and disable the
optimization of the lens focal length. Even then the result may not be
very accurate because the manufacturer specified focal length (or EXIF
focal length) is not very accurate.

You could shoot a 360 degree panorama with the same lens for calibration
purposes, to determine the accurate focal length. The use the calibrated
values in your partial panorama.

> * Panorama editor - it's possible to tilt/shift/bend the projection of

> the panorama, which is great. But can you do it with a reference
> image overlaid on top? Currently, I've been doing some trial and
> error to incrementally tweak the panorama projection until it
> matches in photoshop my rendered reference points (surveyed points
> and Lidar data which I know to be true)

I guess you could add your reference image as a separate source image in
PTGui. Then toggle its visibility using the 'include images' checkboxes
in the Create Panorama tab.

When adding your reference image, make sure it gets its own lens profile
with the proper lens settings in the Lens Settings tab.

> * What image aspect ratio and camera type to be using in 3d to best

> match the panorama (from scouring forums and doing some testing I'm
> currently using Warped-spherical (old style) and image aspect ratio
> of 4:1 to match my override settings of FOV 180, and cylinder height
> of 45.

> * How to align the camera in the first place using cylindrical

> projection. My current workflow is to locate the camera by
> performing a camera match to a couple of the original single frame
> images, and the render the cylindrical projection from that point.
> I've seen posts in 3d forums with people using a spherical
> environment projection, has anyone had any success using this for
> cam alignment?

I don't know, I'm not experienced with 3d modelling software. As far as
I know there are two standard methods to include panoramas in 3d models:
a 360x180 equirectangular 2:1 image, or 6 cube faces. Both can be
exported from PTGui and I assume both can be used in 3ds max. The camera
should always be placed in the middle of the sphere/cube for correct
reprojection.

Joost