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  • How to track the touch vector?

    - by mystify
    I need to calculate the direction of dragging a touch, to determine if the user is dragging up the screen, or down the screen. Actually pretty simple, right? But: 1) Finger goes down, you get -touchesBegan:withEvent: called 2) Must wait until finger moves, and -touchesMoved:withEvent: gets called 3) Problem: At this point it's dangerous to tell if the user did drag up or down. My thoughts: Check the time and accumulate calculates vectors until it's secure to tell the direction of touch. Easy? No. Think about it: What if the user holds the finger down for 5 minutes on the same spot, but THEN decides to move up or down? BANG! Your code would fail, because it tried to determine the direction of touch when the finger didn't move really. Problem 2: When the finger goes down and stays at the same spot for a few seconds because the user is a bit in the wind and thinks about what to do now, you'll get a lot of -touchesMoved:withEvent: calls very likely, but with very minor changes in touch location. So my next thought: Do the accumulation in -touchesMoved:withEvent:, but only if a certain threshold of movement has been exceeded. I bet you have some better concepts in place?

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  • Convolve a column vector

    - by Geoff
    This is an OpenCV2 question. I have a matrix: cv::Mat_<Point3f> points; representing some space curve. I want to smooth it (using, for example a Gaussian kernel). I have tried using: cv::Mat_<Point3f> result; cv::GaussianBlur(points, result, cv::Size(4 * sigma, 1), sigma, sigma, cv::BORDER_WRAP); But I get the error: Assertion failed (columnBorderType != BORDER_WRAP)

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  • Fastest way to find the rotation of a vector

    - by kriss
    I have two 2D vectors, say u and v, defined by cartesian coordinates. Imagine that vectors are needles of a clock. I'm looking for the fastest way to find out, using python, if v is after or before u (or in other words find out in wich half plane is v, regarding to position of u). For the purpose of the problem if vectors are aligned answer should be before. It seems easy using some trigonometry, but I believe there should be a faster way using coordinates only. My test case: def after(u, v): """code here""" after((4,2), (6, 1)) : True after((4,2), (3, 3)) : False after((4,2), (2, 1)) : False after((4,2), (3, -3)) : True after((4,2), (-2, -5)) : True after((4,2), (-4, -2)) : False

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  • Why should "miter" joints be slower than others?

    - by Hanno Fietz
    I'm having a graphics problem on drawing lines in Flash Player, where two lines drawn on top of each other with different thickness don't align properly if I use any other JointStyle than MITER. For pictures of the effect, and for the graphics oriented part of the question, see my post over on doctype. However, there's also a second angle on this problem, which is: why should drawing the "mitered" joints be so much slower than others? This seems to be a problem since at least FP 8, but I couldn't find any detailed info on what the problem might be. Is this just an ordinary bug that didn't get fixed yet, or is there something inherently slower about drawing these joints? For example, they seem to have something to do with square roots, but I seriously lack understanding of what this joint style thing is all about, technically. It just looks like some minor detail a graphic designer might worry about. I'm asking because I'm wondering if I can do something to mitergate, er, mitigate, the problem.

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  • Is it correct to add booleans in order to count the number of true values in a vector?

    - by gerrit
    Is it conceptually correct to sum a vector of booleans? From a mathematical point of view, I would argue it's not: True + True != 2. But it's quite practical to do so still! Example using the vectorised Python library numpy: In [1]: X = rand(10) In [2]: large = X>0.6 In [3]: large.dtype Out[3]: dtype('bool') In [4]: large.sum() Out[4]: 7 I don't like it, but it's very practical. Is this a good practice? Update: the aim is to count the number of true values in a vector.

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  • Animate a e.Graphics.DrawLine with arrowhead

    - by Fer
    I need to "animate" an arrow. It can go in any direction (up, down, left, right and diagonals) and the arrowhead will be at the end. It needs to appear as if it is growing from orgin to the end. To make matters more complicated it has to be in a user control so it is possible to add to the controls collection in the forms and remove it to delete it from the screen, and its background is really transparent (no color.transparent) so i can't paint the background to "clear" the previous line. I have it static already (drawn from origin to end) but i can't animate it. I tried to add a timer in the user control but I fail to get a correct algorithm to calculate the intermediate ends of the line while it is growing. Any help would be appreciated. Thanks

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  • How do I put a vector inside of a struct in Go?

    - by Brian T Hannan
    I'm trying to put a vector variable inside a struct in Google's Go programming language. This is what I have so far: Want: type Point struct { x, y int } type myStruct struct { myVectorInsideStruct vector; } func main(){ myMyStruct := myStruct{vector.New(0)}; myPoint := Point{2,3}; myMyStruct.myVectorInsideStruct.Push(myPoint); } Have: type Point struct { x, y int } func main(){ myVector := vector.New(0); myPoint := Point{2,3}; myVector.Push(myPoint); } I can get the vector to work in my main function just fine, but I want to encapsulate it inside a struct for easier use.

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  • How to interpret situations where Math.Acos() reports invalid input?

    - by Sean Ochoa
    Hey all. I'm computing the angle between two vectors, and sometimes Math.Acos() returns NaN when it's input is out of bounds (-1 input && input 1) for a cosine. What does that mean, exactly? Would someone be able to explain what's happening? Any help is appreciated! Here's me method: public double AngleBetween(vector b) { var dotProd = this.Dot(b); var lenProd = this.Len*b.Len; var divOperation = dotProd/lenProd; // http://msdn.microsoft.com/en-us/library/system.math.acos.aspx return Math.Acos(divOperation) * (180.0 / Math.PI); }

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  • Scalling connected lines

    - by Hristo
    Hello, I have some kind of a shape consisting of vertical, horizontal and diagonal lines. I have starting X,Y and ending X,Y (this is my input - just 2 points defining a line) of each line and I would like to make the whole shape scalable (just by changing the value of a scale ratio variable), so that I can still preserve the proper connection of the lines and the proportions as well. Just for getting a better idea of what I mean: it'd be as if I had the same lines in a vector editor. Would that be possible with an algorithm, and could you please, give me another possible solution if there is no such algorithm ? Thank you very much in advance!

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  • How to resize pdf graphics produced in R using Illustrator

    - by user1648516
    I am making plots in R using the pdf() command. Graphs look perfect and resize nicely in Acrobat Reader. My usual workflow includes manipulating labels etc. in Illustrator, saving as .eps for submission to publishers or inserting in Word. All works fine for single graphs. Now I am trying to combine 4 graphs into one by manually putting them together in an A4 Illustrator document. However, when I resize the standard 7x7 inches pdf graph in Illustrator to fit in one column of an A4 page (ca 3.4 inches wide), all proportions get screwed up, e.g. lines and symbols outlines become way too thick. Using pdf(..., width=3.4, height=3.4) in R messes up all the symbol and font sizes so carefully chosen to produce the original graph. Why can't I resize the graph within Illustrator the same way I can resize the pdf e.g. in Acrobat Reader?

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  • Separating text and graphics in an image

    - by avd
    I dont know whether should I post this question here or not? But if someone knows it, please answer? What are the algorithms for determining which region in an image is text and which one is graphic? Means how to separate such regions? (figure or diagram)

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  • How can I send an std::vector<std::string> over a UNIX socket?

    - by Mike
    For my application, I need to be able to send an std::vector<std::string> over a UNIX socket(local), and get a copy of the vector on the other end of the socket. What's the easiest way to do this with O(1) messages relative to the size of the vector(i.e. without sending a message for each string in the vector)? Since this is all on the same host, and because I control both ends of the socket, I'm not concerned with machine-specific issues such as endinness or vector/string representation.

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  • R graphics plotting a linegraph with date/time horizontally along x-axis

    - by user2978586
    I want to get a linegraph in R which has Time along x and temperature along y. Originally I had the data in dd/mm/yyyy hh:mm format, with a time point every 30 minutes. https://www.dropbox.com/s/q35y1rfila0va1h/Data_logger_S65a_Ania.csv Since I couldn't find a way of reading this into R, I formatted the data to make it into dd/mm/yyyy and added a column 'time' with 1-48 for all the time points for each day https://www.dropbox.com/s/65ogxzyvuzteqxv/temp.csv This is what I have so far: temp<-read.csv("temp.csv",as.is=T) temp$date<-as.Date(temp$date, format="%d/%m/%Y") #inputting date in correct format plot(temperature ~ date, temp, type="n") #drawing a blank plot with axes, but without data lines(temp$date, temp$temperature,type="o") #type o is a line overlaid on top of points. This stacks the points up vertically, which is not what I want, and stacks all the time points (1-48) for each day all together on the same date. Any advice would be much appreciated on how to get this horizontal, and ordered by time as well as date.

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  • Normalized Device Coordinates to window coordinates

    - by okoman
    I just read some stuff about the theory behind 3d graphics. As I understand it, normalized device coordinates (NDC) are coordinates that describe a point in the interval from -1 to 1 on both the horizontal and vertical axis. On the other hand window coordinates describe a point somewhere between (0,0) and (width,height) of the window. So my formula to convert a point from the NDC coordinate system to the window system would be xwin = width + xndc * 0.5 * width ywin = height + ynfv * 0.5 * height The problem now is that in the OpenGL documentation for glViewport there is an other formula: xwin = ( xndc + 1 ) * width * 0.5 + x ywin = ( yndc + 1 ) * height * 0.5 + y Now I'm wondering what I am getting wrong. Especially I'm wondering what the additional "x" and "y" mean. Hope the question isn't too "not programming related", but I thought somehow it is related to graphics programming.

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  • Basic C++ code for multiplication of 2 matrix or vectors (C++ beginner)

    - by Ice
    I am a new C++ user and I am also doing a major in Maths so thought I would try implement a simple calculator. I got some code off the internet and now I just need help to multiply elements of 2 matrices or vectors. Matrixf multiply(Matrixf const& left, Matrixf const& right) { // error check if (left.ncols() != right.nrows()) { throw std::runtime_error("Unable to multiply: matrix dimensions not agree."); } /* I have all the other part of the code for matrix*/ /** Now I am not sure how to implement multiplication of vector or matrix.**/ Matrixf ret(1, 1); return ret; }

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  • C/C++ Bit Array or Bit Vector

    - by MovieYoda
    Hi, I am learning C/C++ programming & have encountered the usage of 'Bit arrays' or 'Bit Vectors'. Am not able to understand their purpose? here are my doubts - Are they used as boolean flags? Can one use int arrays instead? (more memory of course, but..) What's this concept of Bit-Masking? If bit-masking is simple bit operations to get an appropriate flag, how do one program for them? is it not difficult to do this operation in head to see what the flag would be, as apposed to decimal numbers? I am looking for applications, so that I can understand better. for Eg - Q. You are given a file containing integers in the range (1 to 1 million). There are some duplicates and hence some numbers are missing. Find the fastest way of finding missing numbers? For the above question, I have read solutions telling me to use bit arrays. How would one store each integer in a bit?

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  • R from java with no graphics: is it worth moving to JRI

    - by LH
    I have a system set up that's been happily running R from a java servlet, spawning processed & hooking into the process's stdin, stdout, and stderr streams, as in the second andwer to this question. After a system upgrade (that included glibc), the input is no longer reaching the R process.* Until now, 'R --vanilla --slave -f [file] ...' was working fine for me. I also have no swing dependencies right now, so I'm somewhat reluctant to add them. (I may actually not be able to add swing dependencies; am I right that using REngine automatically brings swing in? The examples import all of swing.) Are there advantages to switching to JRI? What changes would I need to make to my R script? (It currently reads from stdin and writes to stdout). I'm not finding the provided examples terribly helpful for how to use JRI in this situation. Thanks for your help & comments. *I can't even tell if the problem is data being written too soon or too late, but that's a separate issue/question; if I move to JRI I'm hoping it all becomes moot.

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  • Rotation in a Vector2d class in Java

    - by wanstein
    I've been working on this for one hour, just can't get it. I have a Vector2d class: public class Vector2d { public double x = 0.0; public double y = 0.0; .... } This vector class has a rotate() method which is causing me trouble. The first snippet seems to make the x and y values smaller and smaller. The second one works just fine! Am I missing something simple here? public void rotate(double n) { this.x = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); this.y = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); } This works: public void rotate(double n) { rx = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); ry = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); x = rx; y = ry; } I just can't spot any difference there

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  • Why use third-party vector libraries at all?

    - by Patrick Powns
    So I'm thinking of using the Eigen matrix library for a project I'm doing (2D space simulator). I just went ahead and profiled some code with Eigen::Vector2d, and with bare arrays. I noticed a 10x improvement in assigning values to elements in the array, and a 40x improvement in calculating the dot products. Here is my profiling if you want to check it out, basically it's ~4.065s against ~0.110s. Obviously bare arrays are much more efficient at dot products and assigning stuff. So why use the Eigen library (or any other library, Eigen just seemed the fastest)? Is it stability? Complicated maths that would be hard to code by yourself efficiently?

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  • Find consecutive sub-vectors of length k out of a numeric vector which satisfy a given condition

    - by user3559153
    I have a numeric vector in R, say v= c(2,3,5,6,7,6,3,2,3,4,5,7,8,9,6,1,1,2,5,6,7,11,2,3,4). Now, I have to find all the consecutive sub-vector of size 4 out of it with the condition that each element of the sub-vector must be greater than 2 and all sub-vector must be disjoint in the sense that non of the two sub-vector can contain same index element. So my output will be: (3,5,6,7),(3,4,5,7),(5,6,7,11). [Explanation: c(2,3,5,6,7,6,3,2,3,4,5,7,8,9,6,1,3,2,5,6,7,11,2,3,4) ]

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  • Quickest way to compute the number of shared elements between two vectors

    - by shn
    Suppose I have two vectors of the same size vector< pair<float, NodeDataID> > v1, v2; I want to compute how many elements from both v1 and v2 have the same NodeDataID. For example if v1 = {<3.7, 22>, <2.22, 64>, <1.9, 29>, <0.8, 7>}, and v2 = {<1.66, 7>, <0.03, 9>, <5.65, 64>, <4.9, 11>}, then I want to return 2 because there are two elements from v1 and v2 that share the same NodeDataIDs: 7 and 64. What is the quickest way to do that in C++ ? Just for information, note that the type NodeDataIDs is defined as I use boost as: typedef adjacency_list<setS, setS, undirectedS, NodeData, EdgeData> myGraph; typedef myGraph::vertex_descriptor NodeDataID; But it is not important since we can compare two NodeDataID using the operator == (that is, possible to do v1[i].second == v2[j].second)

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  • possible to create custom scrollbar graphics without flash?

    - by Joel
    A friend is wanting me to help her convert her flash based website to html. She has an embedded textbox with a scrollbar that is using a flower instead of a normal scrollbar. Avoiding the obvious question of why a user would want a non-standard element to do this task, is it possible to do this without flash?

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