Targeting and contact geometry

Windows uses contact geometry data for the targeting. When the touch hardware reports accurate and reliable contact geometry data, this improves the user's targeting experience. Each digitizer reports the point that it deems to have been intended by the user. When this point does not fall over a valid target, Windows will look at any reported geometry data to identify the most probable target.

Contact geometry

Contact geometry data is used throughout the operating system to disambiguate touch targets and improve users' ability to reliably hit on-screen UI. Applications make use of geometry in painting scenarios and they can use the contact geometry to implement palm rejection or palm detection scenarios in their application layer.

Digitizer must report contact geometry where T (x,y), C (x,y), h' and w' are required variables to represent contact geometry.

HID requirement

The following table summarizes the HID requirement to report contact geometry.

Variable Definition

Tx, Ty

Intended target coordinate

Cx, Cy

Center of the mass X/Y coordinate of the finger contact area. At the same time, this is the center of the rectangle bounding the finger contact area. Can be equal to T.

h'

Height of the oriented (pink) rectangle bounding the finger contact area Reported in physical units (mm). This has the accuracy requirement of +/- 1mm.

Do not report zero.

w'

Width of the oriented (pink) rectangle bounding the finger contact area

Reported in physical units (mm)

This has the accuracy requirement of +/- 1mm.

Do not report zero.

Angle

Counter clock Angle of the oriented (pink) rectangle against the X axis.

Range [0, 360)

Optional Variable. If omitted, assumed axis-aligned.

 

The following figure shows the parameters to represent a contact.

Parameters that represent a contact

 

 

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