美國陸軍，工兵部隊，MS-1 反射式3D立體讀圖鏡《Black Water Museum Collections | 黑水博物館館藏》
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- 2023年10月18日
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United States Army Corps of Engineers MS-1 MAP READING MIRROR STEREOSCOPE
美國陸軍，工兵部隊，MS-1 反射式3D立體讀圖鏡《Black Water Museum Collections | 黑水博物館館藏》
8-10. STEREOVISION
One of the limitations of the vertical aerial photograph is the lack of apparent relief. Stereoscopic vision (or as it is more commonly known, stereovision or depth perception) is the ability to see three-dimensionally or to see length, width, and depth (distance) at the same time. This requires two views of a single object from two slightly different positions. Most people have the ability to see three-dimensionally. Whenever an object is viewed, it is seen twice—once with the left eye and once with the right eye. The fusion or blending together of these two images in the brain permits the judgment of depth or distance.
a. In taking aerial photographs, it is rare for only a single picture to be taken. Generally, the aircraft flies over the area to be photographed taking a series of pictures, each of which overlaps the photograph preceding it and the photograph following it so that an unbroken coverage of the area is obtained (Figure 8-20). The amount of overlap is usually 56 percent, which means that 56 percent of the ground detail appearing on one photo also appears on the next photograph. When a single flight does not give the necessary coverage of an area, additional flights must be made. These additional flights are parallel to the first and must have an overlap between them. This overlap between flights is known as side lap and usually is between 15 and 20 percent (Figure 8-21).
8-10. 立體視覺 (STEREOVISION)
垂直航空照片的局限性之一，在於缺乏明顯的地形起伏感。立體視覺（Stereoscopic vision，或更常被稱為 Stereovision 或深度知覺）是指能夠以立體方式觀看，或同時看見長度、寬度和深度（距離）的能力。這需要從兩個些微不同的位置來觀察同一個物體。大多數人都具備立體視覺的能力。每當觀察一個物體時，其實是看到了兩次——一次是用左眼，一次是用右眼。這兩個影像在大腦中的融合或交匯，使我們能夠判斷深度或距離。
a. 在拍攝航空照片時，很少只拍攝單張照片。通常，飛機會飛越目標攝區並拍攝一系列照片，每一張照片都會與前一張及後一張照片重疊，以獲取該區域完整無間斷的影像覆蓋（圖 8-20）。重疊率通常為 56%，這意味著一張照片中出現的地面細節，有 56% 也會出現在下一張照片中。當單條航線無法提供該區域所需的覆蓋範圍時，就必須進行額外的飛行航次。這些額外的航線會與第一條航線平行，且彼此之間必須有重疊。這種航線之間的重疊稱為旁向重疊 (side lap)，通常介於 15% 到 20% 之間（圖 8-21）。
b. The requirement for stereovision can be satisfied by overlapping photographs if one eye sees the object on one photograph and the other eye sees the same object on another photograph. While this can be done after practice with the eyes alone, it is much easier if an optical aid is used. These optical aids are known as stereoscopes. There are many types of stereoscopes, but only the two most commonly used are discussed in this manual.
(1) Pocket Stereoscope. The pocket stereoscope (Figure 8-22), sometimes known as a lens stereoscope, consists of two magnifying lenses mounted in a metal frame. Because of its simplicity and ease of carrying, it is the type used most frequently by military personnel.
(2) Mirror Stereoscope. The mirror stereoscope (Figure 8-23) is larger, heavier, and more subject to damage than the pocket stereoscope. It consists of four mirrors mounted in a metal frame.
c. One method to orient a pair of aerial photographs for the best three-dimensional viewing is as follows (Figure 8-24):
b. 若一隻眼睛觀看某張照片上的物體，而另一隻眼睛觀看另一張照片上的同一物體，便能透過重疊的照片滿足立體視覺的要求。雖然經過練習後，單憑肉眼（裸眼）也能做到這點，但若使用光學輔助工具會容易許多。這些光學輔助工具稱為立體鏡 (stereoscopes)。立體鏡種類繁多，但本手冊僅討論最常用的兩種。
(1) 袖珍立體鏡 (Pocket Stereoscope)。
袖珍立體鏡（圖 8-22），有時稱為透鏡式立體鏡 (lens stereoscope)，由安裝在金屬框架上的兩個放大透鏡組成。由於構造簡單且易於攜帶，它是軍事人員最常使用的類型。
(2) 反光立體鏡 (Mirror Stereoscope)。
反光立體鏡（圖 8-23）比袖珍立體鏡體積更大、重量更重，且較容易損壞。它由安裝在金屬框架上的四面鏡子組成。
c. 若要定向一對航空照片以獲得最佳的立體觀測效果，可採用以下方法（圖 8-24）：
(1) Arrange the selected pair of photos in such a way that the shadows on them generally appear to fall toward the viewer. It is also desirable that the light source enters the side away from the observer during the study of the photographs.
(2) Place the pair of photographs on a flat surface so that the detail on one photograph is directly over the same detail on the other photograph.
(3) Place the stereoscope over the photographs so that the left lens is over the left photograph and the right lens is over the right photograph.
(4) Separate the photographs along the line of flight until a piece of detail appearing in the overlap area of the left photograph is directly under the left lens and the same piece of detail on the right photo is directly under the right lens.
(5) With the photograph and stereoscope in this position, a three-dimensional image should be seen. A few minor adjustments may be necessary such as adjusting the aerial photographs of the stereoscope to obtain the correct position for your eyes. The hills appear to rise and the valleys sink so that there is the impression of being in an aircraft looking down at the ground.
(6) The identification of features on photographs is much easier and more accurate with this three-dimensional view. The same five factors of recognition (size, shape, shadow, tone, and surrounding objects) must still be applied; but now, with the addition of relief, a more natural view is seen.
(1) 排列選定的一對照片，使照片上的陰影大致朝向觀測者投射。此外，在研讀照片時，光源最好是從遠離觀測者的一側（即照片上方）射入。
譯註：讓陰影朝向觀測者是為了避免「地形反轉」的錯覺（即山峰看起來像山谷，山谷看起來像山峰）。
(2) 將這對照片放置於平坦表面上，使一張照片上的地物細節直接疊在另一張照片的相同細節之上（完全重疊）。
(3) 將立體鏡置於照片上方，使左透鏡位於左側照片上方，右透鏡位於右側照片上方。
(4) 沿著航線 (line of flight) 方向將照片左右分開，直到左側照片重疊區內的某個地物細節直接位於左透鏡下方，而右側照片上的同一細節則直接位於右透鏡下方。
(5) 當照片與立體鏡處於此位置時，應能看見立體影像。可能需要進行些許微調，例如調整航空照片或立體鏡的位置，以取得適合雙眼觀測的焦距與位置。此時山丘會呈現隆起狀，山谷則會凹陷，給人一種彷彿置身飛機上俯瞰地面的感覺。
(6) 透過此種立體視野，識別照片上的地物特徵會變得更加容易且準確。雖然判讀的五大要素（大小、形狀、陰影、色調及周圍相關物體）仍然適用，但現在加上了地貌起伏感 (relief)，能觀察到更自然的景象。
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