Locate3D Overview: Difference between revisions
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{| class=" | Points of interest (POIs) are features of an object that you want to track in X-ray motion trials. They are most commonly used for radiopaque beads implanted in an object whose motion you want to measure. They are distinguished from landmarks, which are object features whose locations you want to calculate once the object pose is known. A common type of landmark is ligament attachment sites. Thus, POIs are used to determine the pose of an object and landmarks are used to calculate locations dependent on the pose. | ||
The recommended procedure for adding POIs to an object is to use xManager to create them and specify their names, radii, and colors (for display in the GUI). Then use Surface3D to specify their XYZ locations in the image data (usually CT). It is important that each POI have a correctly specified radius so that Locate3D's circle-finding algorithm can estimate its size in the X-ray images. | |||
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Revision as of 01:39, 26 June 2020
Language: | English • français • italiano • português • español |
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Locate3D tracks radiopaque beads in X-ray trials. It is most often used to track objects (e.g., bones and implants) with implanted beads. If the object contains three or more beads in fixed locations, and these 3D locations are known relative to the object's CT coordinate system, then the beads' 2D locations in the X-ray images can be used to calculate the object's 3D pose in the X-ray lab frame. Locate3D is thus similar to X4D, except that it uses multiple beads to determine the pose of an object, instead of the contours of the object itself. Locate3D requires that the configuration of the X-ray equipment has been calculated (with CalibrateDSX), and that the locations of the beads in the object's local frame have been determined (with Surface3D).
Digitizing POIs |
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To digitize a POI for the current reporting time, select the POI by clicking on its name in the table in the Points of Interest widget. The table row will be highlighted in blue, and when you move the cursor into one of the X-ray windows, the cursor will change to a circle inside a square, with the POI name to the right. The circle represents the expected size of the POI on the X-ray image, which is dependent on the pixel size of the image and the radius of the POI, which is specified in the subject file. The square represents the region of the image that will be searched for the center of the POI (some of the outer pixels of the POI can be outside the square). The size of the square is controlled by the Click Search Factor parameter. A larger number makes it quicker and easier to digitize POIs, but you don't want the square to contain more than one POI. When you click the left mouse button, Locate3D will search the X-ray pixels within the square to determine which one is the best candidate for the center of the POI. This is done by using the Centroid Threshold parameter to separate the POI pixels from the background, and the Edge Threshold parameter to determine if these pixels represent a circular POI. The POI is assumed to be a bright circle on a dark background, with the center of the POI being the brightest. The 2D coordinates of the POI center in each view are calculated as the weighted center of the pixels above the Centroid Threshold. Once you digitize the POI in one view (you can start with either one), a yellow line is drawn in the other view. This line is the projection of the point in the first view through the field of view of the second view, and its purpose is to help you identify the POI in the other view. You can then digitize the POI in the second view by clicking on a point near the line. If you make a mistake identifying the proper POI in the first view, you can press the Esc key to cancel the process. If you make a mistake after identifying the POI in the second view, you can remove the POI pose by unchecking the pose box in the POI table. Once you have digitized a POI, Locate3D automatically advances the current POI to the next one in the table that does not already have a pose. Once you have identified the POIs for one or more reporting times, you can have Locate3D attempt to automatically identify them for other reporting times using the Propagate POIs command in the Tools menu. See the wiki entry for this command for more details. |
Tutorials
How To: Track Objects Using Points of Interest
Menus
Options Menu |
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Widgets
Points of Interest | ||||
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Points of interest (POIs) are features of an object that you want to track in X-ray motion trials. They are most commonly used for radiopaque beads implanted in an object whose motion you want to measure. They are distinguished from landmarks, which are object features whose locations you want to calculate once the object pose is known. A common type of landmark is ligament attachment sites. Thus, POIs are used to determine the pose of an object and landmarks are used to calculate locations dependent on the pose. The recommended procedure for adding POIs to an object is to use xManager to create them and specify their names, radii, and colors (for display in the GUI). Then use Surface3D to specify their XYZ locations in the image data (usually CT). It is important that each POI have a correctly specified radius so that Locate3D's circle-finding algorithm can estimate its size in the X-ray images.
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POI Parameters | ||||||||||||
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The POI Parameters widget displays the parameters that govern the digitization of POIs in the X-ray images.
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POI Graphs |
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The POI Graphs widget displays graphs of the X, Y, and Z coordinates of the selected POIs for the current trial. As the cursor is moved around the graph a crosshair shows the current coordinates. If the cursor is close enough to one of the data points for a POI it will snap to it and display that point's coordinates in the POI's color. To move the view of a graph in the Y direction, press the left mouse button and drag the cursor up or down. The mouse wheel can also be used to zoom the graph in the Y direction. Press the R key to reset the graph to the default view. The X axis of the graphs cannot be changed. Data points cannot be added or moved via the graphs, but they can be deleted. To select one or more points, press the Ctrl key and then box-select them (hold the left mouse button down while sweeping the diagonal of a box with the cursor). Press the Delete key to delete the points. Press the Esc key to deselect them. |
X-ray Windows |
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The X-ray windows display the X-rays of each view, as well as POIs, POI trails, reference frames, and landmarks. The Points of Interest widget lets you choose which POIs and POI trails to display on the X-rays. The View menu has commands for toggling the display of the reference frame and landmarks of the current object, and the POIs of all of the other objects. The following mouse and keyboard commands can be used in the X-ray windows:
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Settings |
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