[robocup-msrs] Field of View

[Kyle Johns]

Hi Cesar,

Thanks for suggesting a simple experiment to verify the field-of-view.  I think that you are our first user who really cared that this is accurate.

First of all, the FOV shown in the camera entity is the entire FOV and not the half angle.  So 45 degrees represents the entire field of view.  But in the case of a camera that has a wider field of view horizontally than vertically, what does the camera FOV really mean?

We have to rely on the behavior of the XNA CreatePerspectiveFieldOfView matrix function since that is what we are using to define the scene projection.  Its behavior is somewhat different than other graphics systems that I have worked with.  It appears to assign the camera FOV to the vertical dimension.  In other words, for a 320x240 camera with square pixels, the aspect ratio is about 1.33.  A camera FOV of 45 degrees translates to a vertical FOV of 45 degrees and a horizontal FOV of 1.33*45 degrees or about 59.85 degrees.

Cesar,  this is very close to your measured value of 58 degrees.  I attempted to verify this by setting the camera FOV to 68 degrees which should give a horizontal FOV of 90 degrees.  Unfortunately, a camera FOV of about 74 degrees looked much more like a horizontal FOV of 90 degrees.  I'm not sure how to account for the descrepancy.

Bottom line, for the robodugs, the horizontal FOV is around 59 degrees and the vertical FOV is 45 degrees.

-Kyle
________________________________
From: robocup-msrs-bounces at cc.gatech.edu [robocup-msrs-bounces at cc.gatech.edu] On Behalf Of Cesar Flores [cesar7 at gmail.com]
Sent: Wednesday, June 27, 2007 9:56 PM
To: robocup-msrs at cc.gatech.edu
Subject: [robocup-msrs] Field of View


Hi everybody.

We are working in a localization system that uses the horizontal aperture angle. In the robocam there is a variable called FieldOfView = 45. Therefore we assumed that the horizontal aperture angle is 90 degrees as kyle said in another email.

However if this is the correct value, it should be possible to situate the cam in the center of the field and see the center of one goal and the center of one beacon by setting the robudog at 45 from both objects. However the robudog is unable to see both objects at the same time. Instead we calculated by geometry that the horizontal aperture angle is approximately 58 degrees.

We don't know the reason of this. Maybe we understood incorrectly the definition of Field of View. In that case, what does the value FOV of 45 degrees represents?

Thanks!