VRED HTC Vive - Focal length adjustment

[Anonymous]

We have been using VRED + HTC Vive for full scale automotive reviews for the past few months, with considerable success.

Everything has been functioning correctly, however it appears that the focal length when in VR mode is a little too short or fisheye.

The measured scale in VR is correct, however the level of focal length/lens distortion is resulting in vehicles appearing smaller than reality.

Is there a means of adjusting the VR focal length in VRED?

We are not experiencing this issue in other HTC or Steam based applications, which leads me to believe it may be a VRED related issue.

Adjusting the focal length and/or field of view in in viewsets or cameras does not seem to effect the VR focal length at all.

Does anyone have any suggestions as to how we can adjust the VR mode focal length?

[michael_nikelsky]

We have experienced this as well in some scenarios.However, we are just using the the projection matrix steam vr provides us so it is a bit strange that it works in other applications.

Are the scenes you testet modelled in millimeter in the other applications as well? 

We will take a look at it.

[Anonymous]

Thanks for the quick reply Michael,

In fairness, the other applications we use are really just toys compared to VRED, they are basically creative generation sketch tools (Tilt brush, Gravity sketch). So I would say it is difficult to determine whether the lens distortion is present as the software doesn't have the real-world relativity and scale that VRED has.

To me it looks as though the steam projection matrix has the appearance of about a 20-25mm focal length (at least inside of VRED). This would make sense as the wider view would be ideal for gaming. 

What would be ideal is if there was a way to override the projection matrix inside of VRED to have a VR focal length of around 50mm (narrowing the field of view) to better represent the human eye - this should correct the apparent scale distortion we are experiencing. 

Any ideas?

[michael_nikelsky · Accepted solution]

Hi,

I don´t think this impression is related to the focal length/ field of view. The Field of view for these headsets is fixed and it is usually about 100-110 degree. You can´t compare these values to what you have in a normal camera since your eye is basically a very wide angle lens. As I said, the matrix we use is directly from SteamVR and I compared it to the matrix in their examples and those are identical. 

What is more likely is an incorrect interpupillary distance. We use whatever steamVR provides us for this as well although we usually have to convert it to millimeter. However, if this is not matching your eyes you might get the impression that things are too small or too big. I have not really tested it with the current release but you might try to adjust this manually in the stereo settings. I think there is a way to adjust this in steamVR as well but I am not sure where that is.

Kind regards

Michael

[Anonymous]

Thanks again for the quick reply.

Can you elaborate a little further as to how to adjust the stereo settings manually in VRED? Unfortunately this is a bit beyond my current knowledge.

I can see the Manual Frustrum and Manual Projection Matrix settings in the Advanced camera tabs, however I do not know how to use these manual settings correctly and there does not appear to be any in-depth explanation of the function of these setting options in the VRED manual.

Even if I adjust these settings, will Steam simply override any VRED manual settings once launched into OpenVR OMD mode?

[michael_nikelsky · Accepted solution]

You can adjust this setting under Visualization->Stereo->Stereo Settings  but you have to do this after you started OpenVR. But as I said, it is currently untested.

[Anonymous · Accepted solution]

Thanks for your help Michael,

This solution worked perfectly!

We adjusted the IPD/stereo eye separation to a smaller figure and the scale now feels 100% accurate.

Thank you for your quick responses!

Cheers

[michael_nikelsky]

Good to hear that it worked for you. Just curious: What Eye-Separation did you end up using?

[Anonymous]

We actually found an eye separation of around 50-55 did the job.

Obviously this does not represent any of our physical IPD (it is much smaller), however for some reason it seems to work.

On top of the software adjustment inside VRED, individual users are still adjusting the physical IPD on the HTC Vive unit via the adjustment knob to their personal preference (generally around 63-65mm).

The net results of these 2 adjustments is a much more accurate 'feeling' of real world scale.

Thanks for all your help

[ajl]

Thanks for the tip!  I'll give this a try as we've experienced the same smaller than life feeling in VR.  Our product is smaller than a car so I was able to overlay the VR to the actual product which is about 5 foot tall 3 foot wide and could place the controller on the actual object. In VR the virtual controller sits above the item about 50mm.  I ended up scaling the object in VRED by .04 and it was pretty much dead on.

[michael_nikelsky]

If your controllers don´t match between the real world and VRED your setup is not correct. I just verified it and the I could place the controllers in the virtual world at a specific distance and measure this position in the realworld and it was accurate within 1 mm. Try recalibrating your setup and make sure you set the OpenVR origin in VRED do the correct position as well (if you floor is in the xy-plane you should be fine, otherwise you need to adjust it).

I also did a verification of our view matrices and the eye-separation we use is exact. At the moment, turning the wheel on the vive has no effect during runtime though, so you need to set the correct eye distance before you start the OpenVR session (a fix for that is in the making).

But I can also notice the perceived smaller scale, however I am quite confident that this is actually a psychological effect, much like what you see if you start wearing glasses for the first time. Your brain has to adjust for VR  just like it has to adjust in the real world. Problem here is that you probably don´t spent enough time in VR to actually do this.

Kind regards

Michael

[ajl]

Awesome.. thanks for the info Michael! I’ll play around with the setup. That’s great news that it can be so accurate!

[Anonymous · Accepted solution]

I'd definitely agree with Michael here, a difference in controller height is most likely a mis-calibration on your floor height in room set up.

Re-running your room set-up in Steam VR should fix this.

Regarding the perceived scale issue, again I'd agree with Michael that this is a psychological effect to a degree, however we have found that slightly adjusting the eye separation (via the stereo settings in VRED, not the control knob on the headset), to suit each individual user helps to provide a more accurate perception of real world scale.

Across our team we have now spent 100's of hours in VR, and in our experience, simple acclimation to VR over time is not enough to correct the perceived scale issue. The good news is that the stereo eye separation adjustment definitely helps with this issue. The figure is not consistent for each user, but once an individual user has found a setting that 'feels' correct, it is a simple software adjustment to correct the perception of scale.

Thanks again to Michael for the help.