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--- dac_experiments:geometry [2019/05/08 17:31] – [Example: How to find out my own O-matrix] matthias
+++ dac_experiments:geometry [2026/08/12 05:35] (current) – smerkel
@@ Line 12: / Line 12: @@
 More precise and detailed calculations are available in this file, extracted from the fable project: {{ :processing:fable_geometry_version_1.0.8.pdf |}}.
+===== Omega rotation direction =====
+Pay attention to the direction of the omega rotation. On many beamlines, the direction of omega is opposite to the drawing above. Simple take a picture of your sample, with a negative omega value, a positive omega value, and cross-check.
+In the [[fileformat:prm|Input file for ImageD11 (prm)]], the omega rotation direction is defined with the parameter **omegasign**.
+If you are performing a DAC experiment, the shadows from the DAC opening can help to figure out whether your omega rotation axis is positive (as in the drawing above) or negative.
 ===== Detector orientation =====
@@ Line 19: / Line 27: @@
 Here is an example, taken from an old Fable manual (Note: one of the example is wrong, I did see that some times ago, seb)
-{{ :processing:fableimageorientexample.jpg?nolink&400 |}}
+{{ :processing:fableimageorientexample.jpg?nolink&400 |Fig. 2: Example for the 8 possible orientations of a 2D image}}
 Fig. 2: Example for the 8 possible orientations of a 2D image.
@@ Line 33: / Line 41: @@
 Let's do it for the image at ω1 = -20°
-{{ :dac_experiments:orientations.png?600 |}}
+Images, such as the one below, can be generated with the [[software:timeless_viewer|TIMEleSS Viewer]].
+{{ :dac_experiments:orientations.png?600 |Fig. 3: Example for different orientations of the same image}}
-Fig. 3: Example for different orientations of the same image.
+Fig. 3: Example for different orientations of the same image. Those were generated in Fabian, but you can now get the same in the more modern implementation of the [[software:timeless_viewer|TIMEleSS Viewer]].
 === Step 1 ===
@@ Line 47: / Line 57: @@
 Have a look at the sample stage. In which orientation is the rotation taking place? Where is the rotation axis pointing?
-I guess in most setups the rotation axis of ω is pointing to the top or to the bottom (see figure 1). From this you can conclude that the shadow in our diffraction image has to be either on the right or on the left side of the image. With this information you can already exclude 4 out of the 8 possible orientations.
+I guess in most setups the rotation axis of ω is pointing to the top or to the bottom (like the Z-direction in figure 1). From this you can conclude that the shadow in our diffraction image has to be either on the right or on the left side of the image. With this information you can already exclude 4 out of the 8 possible orientations.
 === Step 3 ===