Differences

This shows you the differences between two versions of the page.

--- processing:start [2019/02/08 16:43] – [Grain indexing] matthias
+++ processing:start [2019/06/07 18:00] (current) – [Workflow: Getting a list of grains and their orientations] matthias
@@ Line 5: / Line 5: @@
 {{ ::processing:workflow.jpg?nolink&600 |}}
-===== Software =====
+===== Data collection =====
-The scripts and software you should use for each step are
+Usually, the data is collected in synchrotron facilities by stepwise rotating the sample while the detector is acquiring diffraction images. For more information, click [[dac_experiments:geometry|here]].
-  * Data: you should look at your diffraction data with [[software:fabian|Fabian]]. Pay attention about image orientation and rotation. You can also start looking at diffraction intensity levels, in the background, in the peaks, etc.
-  * Generating backgrounds, median, average images: [[software:imagemath|Image Math]].
-  * Looking at images with background subtracted: [[software:fabian|Fabian]].
-  * Peak extraction: [[software:peaksearch|Peaksearch]]
-  * To be completed...
-===== Workflow for getting grains and their orientations (outline) =====
+===== Workflow: Training with simulated data =====
-The goal of this workflow is to get a list of grains and their specific orientations. You can either start with a simulation to check if your whole workflow is working properly or start with real diffraction data.
+Starting with real data might be complicated if you are a beginner in MGC. Training the actual workflow with simulated data can help you to verify if your workflow is correct. It also makes you familiar with the software. Pitfalls are better visible with artificial data.
-  - Create an input file with the ending //.inp//. It should contain information on instrumentals of the experiment, the grain, the sample, strain, background, peak shape, and so on.
-  - Next you can run the simulation with [[software:polyxsim|PolyXSim]]. This simulation may take a while...
-  - Afterwards, you can look at the output with [[software:fabian|Fabian]].
-  - If you have "real" data, this would be the point when you work on the background (more information on this topic [[software:imagemath|here]]). If you also simulated noise, strain or other things that make your data look more like "real" data, it might be useful to do a background substraction, too.
-  - Now you can search for peaks using the software [[software:peaksearch|PeakSearch]].
-  - In [[software:imaged11|ImageD11]] the found peaks are fitted to the parameters of the sample and experiment, followed by the calculation of the g-vectors.
-  - With the calculated g-vectors, the grains will now be indexed, using [[software:grainspotter|GrainSpotter]].
-  - The calculated g-vectors should then be compared and checked with the simulated g-vectors.
-===== Workflow for getting grains and their orientations (full) =====
+But even when you are working with real data, you can compare your results with the outcome of the simulation to prove if they are reasonable.
-<WRAP center round tip 60%>
+[[processing:workflow_training|Click here to train your workflow with a simulated dataset.]]
-The following chapter deals with the actual use of all the software mentioned above. We describe a path where you can see what you can do with the software when it's working. If you need help with installing or running the software you should check out the wiki pages of the individual software.
-</WRAP>
-==== Producing data by simulation ====
+===== Workflow: Find out the phases in your sample and their cell parameters =====
+This step is actually not part of the MGC but a normal Rietveld refinement. However, it is a necessary step for further processing workflows.
-The purpose of this step is to simulate the outcome of a DAC experiment (grains with random orientations, random strains etc.). It is a possibility to check outcome of an actual experiment. You can also check if your workflow (e.g. the following steps below) is actually working since in a simulation the input parameters are known. When you have real diffraction data already, you can skip this step and open Fabian instead (see below).
+===== Workflow: Getting a list of grains and their orientations =====
+This workflow will provide you with a list of grains, as well as an orientation of each single grain in your sample. [[processing:workflow_dac_data|Click here when you feel ready to rock]]
-The simulation will not only provide 2D diffraction images but also G-vectors, inverse UB matrices (UBi) and some more files. You will get at least 7 different files from the simulation plus the diffraction images. The amount of diffraction images depends on the ω range and the step size you put into the input file. For example, a ω range from -28° to +28° with a step size of 0.5° produces 112 images (numbers from 0 to 111).
+===== ... =====
+More to come ...
-Create an input file with the ending //.inp//. For a start, simply modify an existing one like [[fileformat:inp:basic|this]]. Afterwards, you can run the simulation with [[software:polyxsim|PolyXSim]]. Write the following to the Konsole:
-  PolyXSim.py -i 'some_input_file'.inp
-The 7 different files (which were just mentioned above) are usually created quite fast. The time consuming process is the creation of images. This time highly depends on the parameters you put in the input file, e.g. the amount of grains, the peak shape and if you switched on strain tensors or noise. If you just want to test if the software is working it is wise to use an input file with very simple parameters (only 1 grain, no strain tensors, no noise, small ω range etc.).
-While the simulation is running you can already look at the images, which are already created. For this, open a new tab in the Konsole and open Fabian:
-  fabian.py
-This is convenient because you can already see at this point if your simulation works. And in case it does not, you can stop the simulation process right now and you don't need to wait until all images are created, which can take very long time. While you're at it, check also the O-matrix. You find it in Fabian under //Image// --> //Orientation//. Choose the one which is the same as in your input file.
-==== Working on background ====
-To get rid of the background we now add up all the diffraction images and calculate an average and a median image. Then, every image is subtracted by this average/median image which should remove the background. Of course, if you switched off the background in the previous simulation this process won't change anything. But in case you have real data, this procedure is essential!
-For calculating the average and median you use [[software:imagemath|Image Math]]. Type to the Konsole:
-  image_math_petra 'name stem of the .edf file' 'first image number' 'last image number' median
-  or
-  ./image_math_petra.bin 'name stem of the .edf files including their directory path' 'first image number' 'last image number' median
-For more information on which syntax you should use, check the [[software:imagemath|Image Math wiki page]]. The calculation will create three additional //.edf// files which are automatically stored in the same folder. They share the same name with the other //.edf// files except for an additional letter **m** (for median) in the middle of the name. So look carefully not to oversee them. The images are numbered from 1 to 3. Since they are also //.edf// images, you can also have a look at them with Fabian if you like.
-  * Image //m1// is the **average** image
-  * Image //m2// is the **median** image
-  * Image //m3// is the **??** image
-Next, the actual images have to be subtracted by one of these three images. Usually the m2 image (median) is used for this, because it is less affected by outliers. Before you do this, make sure you have a separate folder to avoid mixing up the actual data with the processed data! Raw data should never be modified!
-Look at the images in Fabian, go to //Image// --> //Correction// --> //Subtract background// and choose the m2 image. Now every image which is currently loaded (including those which you can access by clicking on //next// and //previous//) gets subtracted by this m2 image (median). If it is not simulated data without noise etc. you should see a difference. The peaks should appear clearer.
-==== Peak extraction ====
-From these processed images you can now extract the peaks. Look at some random peaks from several images by zooming in (in Fabian) and check out their intensity. Try to estimate a threshold value which defines how intense a peak must be to be seen by the algorithm. Try to define a threshold, which separates peaks from background (everything above the threshold value is a peak, everything below is background). If you are not sure you can also define several threshold values.
-When you defined one (or more) threshold(s) you can start the [[software:peaksearch|PeakSearch]] algorithm:
-  peaksearch.py -n ../'directory'/'name stem' -f 'first image number' -l 'last image number' -d ../'directory'/'median.edf file' -t 'threshold value 1' -t 'threshold value 2' ...
-To check the outcome of PeakSearch, you can load the peaks, which were found, into Fabian and see if they match the actual peak positions. To do this, you have to go click on //CrystTools// --> //Peaks// --> //Read peaks// and choose the //.flt// file which PeakSearch just created. They should appear as red circles on the diffraction image. You can switch on/off the diffraction spots by clicking on //CrystTools// --> //Peaks// --> //Show//.
-==== Experimental parameters ====
-From these peaks you can now fit the experimental parameters. To do this, open [[software:imaged11|ImageD11]] by typing the following to the Konsole:
-  ImageD11_gui.py
-To load the PeakSearch file click on //Transformation// --> //Load filtered peaks// and choose the //.flt// file from the separate folder with the processed data. Although the image is loaded, it is not plotted automatically, because there are two different ways of plotting. One plotting option is the 2D diffraction image which is similar to Fabian (y/z plot). The other possibility is a cake plot (tth/eta plot). Both options can be accessed by clicking on //Transformation//. Note that plotting both options at once is not making sense because the software is using the same scale for both images (which makes it look weird). To switch from one plot to the other just click on the //Clear// button (bottom of the window) and then plot the other one. //Clear// does only erase the plot, the data is still there.
-Before you check the plots you should enter the measurement parameters. Go to //Transformation// --> //Edit parameters// and enter all parameters for your sample. Remove all check marks from the vary boxes and press //Ok//.
-Next you can have a look at the //tth/eta plot//. Most of the peaks should appear to be on imaginary vertical lines. Zoom in and check, if these lines are completely vertical. If not, you might have strain in your sample. If the line looks like a sinus curve of exactly one period this is due to a wrong beam center. To fix this, go back to //Edit parameters// and activate the check marks for the //y-position// and //z-position// of the detector. Press //Ok// and click on //Fit// for several times until the spots don't move anymore. The imaginary lines should now be completely straight (if you don't have strain). If they are not, you can try to fit other parameters.
-At some point you can click on //Transformation// --> //Add unit cell peaks//. Red tick marks will appear which indicate the expected positions of the vertical lines. With this you can check whether your input parameters (cell parameters, detector distance, ...) were correct.
-==== Grain indexing ====
-This step is necessary to get the G-vectors from your grains.
-In ImageD11, click on //Indexing// --> //Assign peaks to powder rings// (nothing will happen), then click on //Transformation// --> //Compute g-vectors// and finally //Transformation// --> //Save g-vectors//. Make sure the file gets the ending //.gve//.
-To index the grains you need [[software:grainspotter|GrainSpotter]] and an //.ini// file. If you previously did a simulation with [[software:polyxsim|PolyXSim]], you already have an //.ini// file which you can modify for your purposes. Make sure to keep the original and do only modify a copy. For details on what this //.ini// file should contain, check out the [[software:grainspotter|GrainSpotter wiki page]], the [[fileformat:ini|.ini wiki page]] or the [[GrainSpotter manual]]. Make sure the //.ini// file contains the right //.gve// file (the one you just created).
-To start GrainSpotter, type the following to the Konsole:
-  GrainSpotter.0.90 'some_file_name'.ini
-  or
-  grainspotter 'some_file_name'.ini
-For more information on which syntax you should use, check the [[software:grainspotter|GrainSpotter wiki page]].
-The outcome of the GrainSpotter algorithm is three files: a //.gff// file, a //.ubi// file and a //.log// file. These files contain information on the amount of grains it found, their UBi matrices and some more info. If you are already working with real data, you can now interpret what you got.
-==== Check your workflow ====
-If you did a simulation in advance, this is the time to check if you (and the software) did a good job or not. Open the //.gve// file which was just created by GrainSpotter and compare the g-vectors with the ones which were created by the simulation at the very beginning. The UBi matrices can be in a different order but should be the same. Remember that some rows or columns within the matrix can be inverted due to symmetry.
-<WRAP center round box 60%>
-**Example**: The following two matrices are created by PolyXSim (left) and by GrainSpotter (right). The symmetry of the material is tetragonal. This means that //a-axis// and //b-axis// are identical and cannot be distinguished by the software. So row 1 and row 2 are exchangeable. In addition to that, their sign is opposite. But the software cannot distinguish the polarity of the grain either. So based on this the two UBi matrices are identical.
-  From PolyXSim             From GrainSpotter
-.582  2.186 -0.098       4.411  0.360  1.912
-  -4.411 -0.360 -1.912      -3.582 -2.186  0.098
-.133  1.995  0.247       0.133  1.995  0.247
-</WRAP>
-If all the simulated UBi matrices match the calculated ones, you can be quite sure that your workflow is running properly. In a next step you can work with real data.