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annotate OrthancStone/Resources/Documentation/Coordinates.txt @ 1810:b05d5f0d014f

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author Sebastien Jodogne <s.jodogne@gmail.com>
date Thu, 20 May 2021 19:11:44 +0200
parents 20a0aba0ede5
children
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1
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2 Some notes about the coordinate systems
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3 =======================================
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5 Different systems
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6 -----------------
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7
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8 * "World" coordinates refer to (x,y,z) positions, typically expressed
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9 in millimeters (according to the DICOM conventions), which allows to
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10 define volumes and 3D cutting planes.
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11
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12 As explained below, those coordinates actually correspond to
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13 "patient" coordinates if rendering DICOM images.
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15 The "world" coordinates are *not* used by the Stone Web viewer,
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16 because the latter is a 2D application.
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17
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18 * "Scene" coordinates refer to (x,y) positions, typically expressed in
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19 millimeters (as a byproduct of world coordinates), which allows to
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20 define the 2D geometric elements that are part of the scene, and
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21 Y-axis pointing downward.
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22
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23 * "Canvas" coordinates refer to (x,y) subpixel positions that will be
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24 blitted by a compositor onto a drawing canvas. The units are
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25 floating-point pixels, with (0,0) corresponding to the center of the
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26 display surface, and Y-axis pointing downward. The "canvas"
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27 coordinates modify the "scene" coordinates according the zoom/pan
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28 specified by the user.
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29
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30 * "Pixels" coordinates refer to standard integer (x,y) coordinates of
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31 the surface in memory. (0,0) is the top-left pixel.
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34 Relations between 2D and 3D
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35 ---------------------------
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37 * The 3D coordinates are expressed in the PATIENT system, *not* the
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38 "gantry" coordinates. As a consequence, the tags "Image Position
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39 Patient" (0020,0032) and "Image Orientation Patient" (0020,0037)
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40 describe the 3D geometry of a slice.
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42 * The tag "Patient Position" (0018,5100) could be used to convert from
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43 patient coordinates to gantry coordinates, but this would be useful
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44 to device manufacturers, whereas Stone primarly deals with users of
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45 modalities.
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47 * The "Image Position Patient" gives the 3D coordinates of the CENTER
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48 of the top-left voxel of slice.
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50 * In 2D compositors, the origin of a texture corresponds to the CORNER
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51 of the top-left pixel of the texture (*not* to the center of this
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52 pixel). Roughly speaking, the operation "floor()" must be applied to
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53 move from canvas coordinates (floating-point numbers) to pixel
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54 coordinates in the image buffer (integer numbers).
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56 * The classes deriving from "IVolumeSlicer" must pay to attention to
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57 convert from centers of 3D voxels to bounding boxes of 2D pixels.