Home Forums Software Development Finding the Depth for the Active Display Area Calculator

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    Mark Castle

    I’m trying to set the active display area for my EyeX, but I’m not quite sure that I understand what the depth offset is. Is it just the distance from the front of the screen to the backside of the eye tracker?

    Height and Depth Offset Diagram from Tobii Active Display Area Calculator

    The depth offset should typically be positive, meaning that the eye tracker is in front of the screen.

    The height offset should be zero if the top of the eye tracker is aligned with the bottom of the screen, positive if it is above the bottom of the screen, or negative if it is below the bottom of the screen.

    The diagram shown doesn’t make much sense to me. For example, what are the three shapes supposed to be representing?

    Jenny [Tobii]

    Hi Mark,

    First of all, the reason you are not using the screen setup on the EyeX Settings panel is because you want to use your EyeX Controller without a computer monitor, right? (As stated in this topic: http://developer.tobii.com/community/forums/topic/calibration-without-a-screen/)

    To be able to set the active display area I gather you have downloaded the Tobii Gaze SDK and found your way to the tools folder and displayareacalc.html. The diagram you are referring to is the one in step 3.

    To understand the diagram, please start by taking a look at the diagram of step 2. The colors in the two diagrams are corresponding: the blue color represents the screen area of the monitor, the light gray color represents the monitor frame, and the dark gray color represents the eye tracker.

    When attached to a monitor the eye tracker is placed just below the screen area and slightly tilted upwards so the illuminators and camera are directed towards the eyes of the person in front of the monitor. The depth offset is the distance from the top edge of the front side of the eye tracker to the monitor screen surface (perpendicular to the screen surface).

    The tilt angle is given by the geometry of the housing and the mounting area of the specific eye tracker and has to be specified in step 4. The default values that can be loaded using the buttons assumes the mounting angle that would result from mounting the eye tracker on a monitor frame with a surface parallell to the screen surface.

    I hope this clarifies what the diagrams mean and what you need to measure and calculate for the non-screen case.


    I’m sorry to post here from an old post, I actually haven’t found how to set up a new topic, and maybe it’s just better to do it here.

    I try to understand the content of the paremeters of the tools (the html page referred above) but I just dont get it. Actually, one of them is really unclear to me: the vertical distance optical center to mid front.

    I wanted to test it a bit, and to do so, I have made as if the eye tracker’s front face was parallal to the display and aligned with the middle and bottom of the display. Therefore, in that case, all offset values in step 2 and 3 are 0.
    Then, I only change the default value (using EyeX for instance) of the mounting angle, in the step 4, to 0 since it’s parralal.
    If the display were 200*50 (it is just an example), then I would expect to get the following values:
    Top left: (-100.0, 60.0, 0) mm
    Top right: (100.0, 60.0, 0) mm
    Bottom left: (-100.0, 10.0, 0) mm
    because it is clearly said in the SDK documentation that the active display coordinates are to be expressed in the UCS, which has an origine at the centre of the front face of the eye tracker.

    But, instead, I have :
    Top left: (-100.0, 60.0, 10.3) mm
    Top right: (100.0, 60.0, 10.3) mm
    Bottom left: (-100.0, 10.0, 10.3) mm.
    I can see here the effect of the vertical distance optical center to mid front on the depth, but I just dont understand what it can be. If it is a depth, why it’s not “included” in the the value of the depth in step 3 ?

    As far as I can understand, only the display dimensions, offsets from step 2 and 3, the distance between the top edge of the eye tracker and the centre (“distance mid from to top front” in step 4) and the mounting angle should be needed… Where do I get it wrong ?

    Thanks a lot for your help,

    Best regards,

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