{"id":309,"date":"2021-11-15T12:27:54","date_gmt":"2021-11-15T12:27:54","guid":{"rendered":"http:\/\/www.calm-ebsd.com\/?page_id=309"},"modified":"2021-12-26T16:46:19","modified_gmt":"2021-12-26T16:46:19","slug":"projection-center-pc","status":"publish","type":"page","link":"https:\/\/www.calm-ebsd.com\/index.php\/news\/requirements\/projection-center-pc\/","title":{"rendered":"Projection center PC"},"content":{"rendered":"\n

The projection center enables<\/strong> the reverse transformation<\/strong> of a projection<\/strong> image into<\/strong> its original 3-dimensional <\/strong>translation-periodic lattice<\/strong>.
From this becomes clear that the more accurate<\/strong>ly this<\/strong> projection point<\/strong> is determined, the more trustful<\/strong> the<\/strong> result<\/strong>ing reverse transformation can be. <\/p>\n\n\n\n

PC is described by a coordinate triple [PCx<\/sub>,PCy<\/sub>,PCz<\/sub>]<\/strong>. <\/p>\n\n\n\n

\"\"<\/figure>
\n

Projection center as defined in CALM describes the point where the primary electron beam hits the sample surface. The vertical projection onto the detector screen defines the pattern center.<\/em>
Any eucentric<\/span> tilt of the sample does not change PC but any tilt of the detector does.<\/em>

<\/p>\n<\/div><\/div>\n\n\n\n

Pattern center<\/strong>:<\/span> In the past, often this term is used describing only [PCx<\/sub>,PCy<\/sub>]. Then, PCz<\/sub> is either ignored or referred to as detector distance (DD).<\/p>\n\n\n\n

Please note:<\/span> Each commercial EBSD supplier uses<\/strong> his own definition<\/strong>. CALM uses an “aspect-ratio free” input in the user interface matching to DynamicS (Bruker).
Aztec (Oxford Instr.) stores the projection center in the exported tiff-file at the end. It is readable by any ASCII editor, e.g. Notepad++. The coordinate [pcy<\/sub>,pcy,<\/sub>dd] can be transferred into CALM data using the following equations. F represents the form factor of the image, i.e., horizontal numer divided by vertical number of pixels.
OIM (EDAX-TSL) displays the projection center as [x*,y*,z*]. The transformation is identical since for a circular image F=1. \u00b7<\/p>\n\n\n\n

<\/td><\/td><\/td>PCx<\/sub><\/td>PCy<\/sub><\/td>PCz<\/sub><\/td><\/tr>
Aztec<\/td>[pcy<\/sub>,pcy,<\/sub>dd]<\/td> F = 1244\/1024<\/td>pcx<\/sub><\/strong><\/span><\/td>1 \u2012 (pcy<\/sub>\u00b7 F<\/strong><\/span>)<\/td>dd \u00b7 F<\/strong><\/span><\/td><\/tr>
OIM<\/td>[x*,y*,z*]<\/td><\/td>x*<\/span><\/strong><\/td>1 \u2012 y*<\/span><\/strong><\/td>z*<\/span><\/strong><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

[PCx<\/sub>,PCy<\/sub>,PCz<\/sub>] should be preferably entered in CALM before trace and bandwith definition since PC affects both.. <\/p>\n\n\n\n

The use of a reference pattern<\/p>\n\n\n\n

For very precise measurements the exact PC<\/strong> is requested for each<\/strong> individual Kikuchi pattern <\/strong>seperately, i.e. collect for each pattern an additional pattern, preferably from a cubic or a very well-known phase. The acquisition conditions<\/strong> have to be exactly the same<\/strong>.<\/span><\/p>\n\n\n\n

This means…
Either:<\/em><\/span><\/span> Don’t move the beam <\/strong>to the diffracting particle but shift the stage<\/strong> until the particle is in the center of the SEM image.
Or:<\/span> <\/em><\/span>Collect<\/strong> the pattern at very high magnifaction<\/strong>. Then any movement of the beam is comparatively small compared to the size of an image pixel.<\/p>\n\n\n\n

Example:<\/strong> For a detector screen of 38×28 mm (what is slightly bigger than the really captured image size) and a resolution of 1342×1024 pixels the effective distance between two adjacent image pixels is approximately 28\u00b5m. This means, if two measurement positions (between reference and interesting phase) have a distance of 28\u00b5m, their pattern centers are shifted by one pixel against each other. For the hypothetically used pattern this difference changes PC by about \u00b10.001<\/em>. <\/p>\n\n\n\n

Please note:<\/span> Possible charging<\/strong> unpredictably shifts the beam<\/strong> position and so the projection center PC. <\/em> <\/p>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

The projection center enables the reverse transformation of a projection image into its original 3-dimensional translation-periodic lattice. From this becomes clear that the more accurately this projection point is determined, the more trustful the resulting reverse transformation can be. PC Read More …<\/a><\/p>\n","protected":false},"author":3,"featured_media":0,"parent":412,"menu_order":1,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"_links":{"self":[{"href":"https:\/\/www.calm-ebsd.com\/index.php\/wp-json\/wp\/v2\/pages\/309"}],"collection":[{"href":"https:\/\/www.calm-ebsd.com\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.calm-ebsd.com\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.calm-ebsd.com\/index.php\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.calm-ebsd.com\/index.php\/wp-json\/wp\/v2\/comments?post=309"}],"version-history":[{"count":55,"href":"https:\/\/www.calm-ebsd.com\/index.php\/wp-json\/wp\/v2\/pages\/309\/revisions"}],"predecessor-version":[{"id":1758,"href":"https:\/\/www.calm-ebsd.com\/index.php\/wp-json\/wp\/v2\/pages\/309\/revisions\/1758"}],"up":[{"embeddable":true,"href":"https:\/\/www.calm-ebsd.com\/index.php\/wp-json\/wp\/v2\/pages\/412"}],"wp:attachment":[{"href":"https:\/\/www.calm-ebsd.com\/index.php\/wp-json\/wp\/v2\/media?parent=309"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}