Gaze and Fixation Data Streams returning negative coordinates?

[Manveer]

Hi,

I’m currently working on a test application to collect the gaze and fixation x and y coordinates when a user looks at a full screen image. I understand the difference between Client and Screen coordinates from the SDK guide, and in this case, I want to use the screen coordinates since I want to get the coordinates of the actual pixels on the screen.

I looked at the samples Minimal Gaze Data Stream and Minimal Fixation Data Stream, and both seem to return negative coordinates for x and y at various points.

For instance, the x and y values of TX_GAZEPOINTDATAEVENTPARAMS is negative.

I’m using only one monitor (windows 7 laptop with 1600×900), and my screen DPI value is at a default 100%.

Therefore, I wanted to know if the negative values I’m seeing are only because tobii has seen that the exact coordinate is off the screen? Since I noticed that the negative coordinates only occur really near the borders of the screen, but I cannot be sure of this.

Please help me clarify if it’s supposed to return negative values for the coordinates, and if not, what could possibly be the problem?

Thanks in advance with all your help, I really appreciate it!

[Jenny [Tobii]]

Hi Manveer,

The coordinates of the Gaze Point data stream and the Fixation data stream are (x,y) points in pixels on the Virtual Screen. This is how the Virtual Screen is described on MSDN:
https://msdn.microsoft.com/en-us/library/dd145136(v=vs.85).aspx

Since (0,0) is the upper left corner of the primary screen, whenever you look to the left or above the primary screen’s borders you will get negative values for the x and/or y coordinate in these EyeX data streams.

[Author]

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