Period 3
  
Hey there!! We continue to develop our expertise in 3-view drawings. Since last time the students have learned to dimension their drawings. 


Orthographic projection




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This article is about technical drawings. See Orthographic projection (geometry) for linear transformations and Orthographic projection (cartography) for maps. For the language concept, see orthography. 





Image of a three-dimensional object inside a box with transparent walls




Example of orthographic drawing from a US Patent (1913), showing two views of the same object. Third angle projection is used. 



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Example of orthographic drawing from a US Patent (1913), showing two views of the same object. Third angle projection is used.


Orthographic projection is a means of representing a three-dimensional object in two dimensions. It uses multiple views of the object, from points of view rotated about the object's center through increments of 90°. Equivalently, the views may be considered to be obtained by rotating the object about its center through increments of 90°.


The views are positioned relative to each other according to either of two schemes: first-angle or third-angle projection. In each, the appearances of views may be thought of as being projected onto planes that form a transparent "box" around the object:










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[edit] First-angle projection


In first-angle projection, each view of the object is projected in the direction (sense) of sight of the object, onto the interior walls of the box; that is, each view of the object is drawn on the opposite side of the box:


Image of object in box, with views of object projected in the direction of sight onto walls using first-angle projection


A two-dimensional representation of the object is then created by "unfolding" the box, to view all of the interior walls:


Similar image showing the box unfolding from around the object


Image showing orthographic views located relative to each other in accordance with first-angle projection


This produces two plan views and four side views.




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