transformation | 易学教程

Quaternion rotation without Euler angles

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问题 In this comment it was strongly suggested that we should never use Euler angles. I understand that there are some limitation to Euler angles, most notably gimbal lock, but I'd like to know the best technique, or the set of techniques, that one typically uses in the absence of Euler angles? Most dicussions on this topic involve converting from an Euler angle to a quaternion and that is a simple thing to do. But the only way I have ever read about doing rotation without Euler angles at all is

Velocity Template engine - key-value-map

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问题 I have some problems wo use a key-value-map into Velocity. Someone has an example of this functionality? $myMap ={} $myMap.put("mykey1", "myvalue") $myMap.delete("mykey1") $myMap.getValue("mykey1") 回答1: As Nathan said, you should use: #set ($myMap = {}) to create a new map and assign it to a variable. Now, why is the put call printed. Anything that is not inside a directive, like #set(not printed) or #if(not printed) or #foreach(again not printed) , is printed, including free text, variables,

iOS: Movie player view doesn't rotate

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问题 I want to rotate my movie player view explicitly (not using Autorotation delegate) . I wrote following code for that and also put comments in it. The parent view of movie player does rotate but not movie player view itself. Could someone please assist me here what I am doing wrong? Thanks. #import "CustomMoviePlayer.h" #define degreesToRadian(x) (M_PI * (x) / 180.0) #define radianToDegrees(x) ((x) * 180.0/M_PI) @implementation CustomMoviePlayer @synthesize moviePlayer, myParentViewController;

How to set axis (triad) at fixed position on screen in JavaFX?

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问题 How to set axis (triad) at fixed position on screen in JavaFX? I am currently developing one application in which I want to show axis (triad) at fixed position on my screen (i.e. bottom-left corner). I want rotation of axis should be in sync with the main object. Zoom and Translate operation should not be applied to axis. But I am facing some difficulties to show axis at specific position on screen. I have used screenToLocal method to get fixed position in scene but it only returns Point2D

apply all transform matrices

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问题 I am looking for a possibly fast way to apply all transform matrices of a given svg-graphic. In other words: the algorithm should remove all "transform" attributes and transform all coordinates of the graphic to absolute coordinates. Is their any library that can do this, or is their any SVGDomInterface method that coulld do that? EDIT:: If I call the consolidate method like this: $.each( svg.find( 'path' ), function( i ){ this.transform.baseVal.consolidate(); }); nothing happens, if i call

OpenCV Transform using Chessboard

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问题 I have only just started experimenting with OpenCV a little bit. I have a setup of an LCD with a static position, and I'd like to extract what is being displayed on the screen from the image. I've seen the chessboard pattern used for calibrating a camera, but it seems like that is used to undistort the image, which isn't totally what I want to do. I was thinking I'd display the chessboard on the LCD and then figure out the transformations needed to convert the image of the LCD into the ideal

How to get rotation, translation, shear from a 3x3 Homography matrix in c#

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问题 I calculated the 3x3 homography matrix and I need to get rotation, translation, shear and scale to use them as parameters in the windows8 media element attributes ?! 回答1: see https://math.stackexchange.com/questions/78137/decomposition-of-a-nonsquare-affine-matrix def getComponents(normalised_homography): '''((translationx, translationy), rotation, (scalex, scaley), shear)''' a = normalised_homography[0,0] b = normalised_homography[0,1] c = normalised_homography[0,2] d = normalised_homography

Hibernate SQL transformation fails for Enum field type

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问题 I am using a SQL query and then transforming the result using Hibernates's Transformers.aliasToBean() . One of the columns in my query is an enum. The transformation somehow fails for the enum. What should I do? Which datatype should I use? I want more than 1 character to transform the result into my enum type. This is how the simplified version of my query/code looks like ( b is an enum in the table profiles): session.createSQLQuery("select a, b from profiles").setResultTransformer

Opengl order of matrix transformations

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问题 Let's say I have a blue 3D box (where the top side is red colored). Now I call glScalef(1, 10, 1). Then I call glRotatef(90, 0, 1, 0). Then i render the cube. What i expected is to see the the red side facing and stretched towards the screen (along the Y axis of the model). But what im seeing is this: The red side is facing the screen (as expected). But the stretch is occurring on the Y axis of the view space (not the model). I do know that if I set the scale along the Z axis, then i'll get

The easiest way to transform collection to array?

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Suppose we have a Collection<Foo> . What is the best (shortest in LoC in current context) way to transform it to Foo[] ? Any well-known libraries are allowed. UPD: (one more case in this section; leave comments if you think it's worth to create another thread for it): What about transforming Collection<Foo> to Bar[] where Bar has constructor with 1 parameter of type Foo i.e. public Bar(Foo foo){ ... } ? doublep Where x is the collection: Foo[] foos = x.toArray(new Foo[x.size()]); Alternative solution to the updated question using Java 8: Bar[] result = foos.stream() .map(x -> new Bar(x))