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--- other:dsx:x4d:tutorials:track_multiple_bones [2024/07/17 15:43] – removed sgranger
+++ other:dsx:x4d:tutorials:track_multiple_bones [2025/06/04 14:57] (current) – Cleaned up page and added section headers. Added reference to basic guide. wikisysop
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+====== Track Multiple Bones ======
+Before beginning this tutorial, ensure that you are familiar with the steps in the [[other:dsx:x4d:tutorials:basic_bone_tracking|Basic Bone Tracking]] guide.
+===== Overview =====
+Unless the bones overlap in the X-ray images, it is better to track bones one at a time. This is because for each iteration the optimizer randomly positions each bone and then evaluates the fit of all of them together. If one bone was moved to a slightly better pose while the others were moved to worse ones (a common occurrence), the overall fit would be worse and the poses of all bones would be discarded.
+===== Tracking Two Bones =====
+Even if there is overlap of bones, it is often preferable to track them separately. In these cases, a good strategy is to track one bone first, then to lock it in place and track a second bone with the first one still active.
+For example, when tracking the bones at the knee there is often substantial overlap between the femur and the patella. The recommended strategy is as follows:
+  - select just the femur;
+  - track the femur by itself in all frames;
+  - select both the femur and patella;
+  - uncheck the femur box in the [[Other:DSX:X4D:Object_Tracking|Object Tracking]] widget so that the femur remains fixed in its previously calculated poses; and
+  - optimize to track the patella.
+The femur’s DRR will be included in the optimization, but the femur pose will not change in each frame.