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原文鏈接：https://developers.google.com/tango/overview/depth-perception
深度感知技術能讓應用感知現實世界中物體之間的距離。想要讓Tango 設備具備該能力，設備生產廠商可以從幾個常見的深度感知技術中選擇一種并實現之：結構光（Structured Light），TOF 相機（Time of Flight），立體相機。（關于這三種技術，參見 《High-Fidelity Augmented Reality Interactions》——譯者注）。其中，前兩種技術需要使用紅外投影儀和紅外線傳感器，而立體相機不需要。
深度感知技術可以應用于諸多場景中：
在游戲中檢測玩家向墻壁或其他物體移動；結合使用深度感知和運動追蹤技術，能夠測量某區(qū)域中同一片點云在不同坐標幀中的距離；結合使用深度數據和色彩圖像數據，在渲染紋理或網格（關于 Unity Mesh 參見 《Unity Mesh 初體驗》——譯者注）時查找點云中的色彩；當前的tango設備是為室內場景設計的，在室內大約 0.5-4米的距離范圍內效果最優(yōu)。這種設計能夠最好的兼顧紅外線和數據計算帶來的耗電，并保證獲取的深度數據最優(yōu)。而對于近距物體掃描或手勢檢測，效果卻不理想。 有些設備是使用相機觀測紅外線來實現深度感知的，這些設備在某些情景下無法實現精確的深度感知。比如，由于日光或白熾燈中含有大量的紅外線，所以日光或白熾燈覆蓋的區(qū)域，以及無法反射紅外線的物體，都是無法被感知的。
tango API 以點云的形式返回深度數據。點云中包含當前環(huán)境中能夠獲取的盡可能多的(x, y, z)坐標，每一維數據都是浮點型，單位是米，表示其在坐標幀中位置。
更多信息，見 TangoPointCloud 結構體。
Depth Perception gives an application the ability to understand the distance to objects in the real world. To implement Depth Perception, manufacturers of Tango devices can choose among common depth technologies, including Structured Light, Time of Flight, and Stereo. Structured Light and Time of Flight require the use of an infrared (IR) PRojector and IR sensor; Stereo does not.
Depth Perception can be useful in a number of ways:
A game might want to detect when the user is approaching a wall or other object in the area and have that be part of the gameplay.By combining Depth Perception with Motion Tracking, the device can measure distances between points in an area that aren’t in the same frame.Depth data can be associated with the color image data to look up the color for a point cloud for texturing or meshing.Current devices are designed to work best indoors at moderate distances (0.5 to 4 meters). This configuration gives good depth at a distance while balancing power requirements for IR illumination and depth processing. It may not be ideal for close-range object scanning or gesture detection.
For a device that relies on viewing IR light using its camera, there are some situations where accurate Depth Perception is difficult. Areas lit with light sources high in IR like sunlight or incandescent bulbs, or objects that do not reflect IR light, cannot be scanned well.
The Tango APIs provide a function to get depth data in the form of a point cloud. This format gives (x, y, z) coordinates for as many points in the scene as are possible to calculate. Each dimension is a floating point value recording the position of each point in meters in the coordinate frame of the depth-sensing camera.
For more information, see the TangoPointCloud struct API reference.
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