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  • minimum enclosing rectangle of fixed aspect ratio

    - by Ramya Narasimha
    I have an Image with many rectangles at different positions in the image and of different sizes (both overlapping and non-overlapping). I also have a non-negative scores associated with each of these rectangles. My problem now is to find one larger rectangle *of a fixed (given) aspect ratio* that encloses as many of these rectangles as possible. I am looking for an algorithm to do this, if anyone has a solution, even a partial one it would be helpful. Please note that the positions of the rectangles in the image is fixed and cannot be moved around and there is no orientation issue as all of them are upright.

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  • Good way to identify similar images?

    - by Nick
    I've developed a simple and fast algorithm in PHP to compare images for similarity. Its fast (~40 per second for 800x600 images) to hash and a unoptimised search algorithm can go through 3,000 images in 22 mins comparing each one against the others (3/sec). The basic overview is you get a image, rescale it to 8x8 and then convert those pixels for HSV. The Hue, Saturation and Value are then truncated to 4 bits and it becomes one big hex string. Comparing images basically walks along two strings, and then adds the differences it finds. If the total number is below 64 then its the same image. Different images are usually around 600 - 800. Below 20 and extremely similar. Are there any improvements upon this model I can use? I havent looked at how relevant the different components (hue, saturation and value) are to the comparison. Hue is probably quite important but the others? To speed up searches I could probably split the 4 bits from each part in half, and put the most significant bits first so if they fail the check then the lsb doesnt need to be checked at all. I dont know a efficient way to store bits like that yet still allow them to be searched and compared easily. I've been using a dataset of 3,000 photos (mostly unique) and there havent been any false positives. Its completely immune to resizes and fairly resistant to brightness and contrast changes.

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  • Apache rewrite_mod: RewriteRule path and query string

    - by 1ace
    I currently have a website with a standard web interface on index.php, and I made an iPhone-friendly version in iphone.php. Both pages handle the same arguments. It works fine when I manually go to .../iphone.php, but I'd like to rewrite anything on .../path/ and .../path/index.php to iphone.php if %{HTTP_USER_AGENT} contains mobile, and optionally add the query string (not sure if/when I'd need to add it). So far, this is what I have in my .../path/.htaccess: RewriteEngine On RewriteCond %{HTTP_USER_AGENT} ^.+mobile.+$ [NC] RewriteRule index.php?(.*) iphone.php?$1 [L] RewriteRule index.php iphone.php [L] The problems are, it matches index.php in any subfolder, and it won't match .../path/?args… Special thanks to anyone who can correct/simplify/optimize anything =)

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  • What does it mean to do/determine something "programmatically"?

    - by Chris Lutz
    Programmatically. (alt. programmically) I've never used it, but I see it in questions a lot, i.e. "How to programmatically determine [insert task here]". Firefox immediately tells me that neither of these two words are real (at least, it doesn't recognize them). I've also never seen them used anywhere but here. 1) What does it mean to do/determine something "programmatically"? 2) Why do so many people ask how to do/determine something "programmatically"? Isn't it assumed that, if you're asking how to do something on a programming help board, you're asking how to do it "programmatically"? 3) Why is it that I've never seen the word "programmatically" anywhere else?

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  • How do you avoid an invalid search space in a genetic algorithm?

    - by Dave
    I am developing a GA for a school project and I've noticed that upon evaluating my functions for fitness, an individual is equivalent to its inverse. For example, the set (1, 1, -1, 1) is equivalent to (-1, -1, 1, -1). To shrink my search space and reach a solution more efficiently, how can I avoid my crossovers from searching in this second half of the search space?

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  • Task vs. process, is there really any difference?

    - by DASKAjA
    Hi there, I'm studying for my final exams in my CS major on the subject distributed systems and operating systems. I'm in the need for a good definition for the terms task, process and threads. So far I'm confident that a process is the representation of running (or suspended, but initiated) program with its own memory, program counter, registers, stack, etc (process control block). Processes can run threads which share memory, so that communication via shared memory is possible in contrast to processes which have to communicate via IPC. But what's the difference between tasks and process. I often read that they're interchangable and that the term task isn't used anymore. Is that really true?

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  • Mutual Information / Entropy Calculation Help

    - by Fillip
    Hi, Hoping someone can give me some pointers with this entropy problem. Say X is chosen randomly from the uniform integer distribution 0-32 (inclusive). I calculate the entropy, H(X) = 32 bits, as each Xi has equal probability of occurring. Now, say the following pseudocode executes. int r = rand(0,1); // a random integer 0 or 1 r = r * 33 + X; How would I work out the mutual information between the two variables r and X? Mutual Information is defined as I(X; Y) = H(X) - H(X|Y) but I don't really understand how to apply the conditional entropy H(X|Y) to this problem. Thanks

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  • Are .NET's regular expressions Turing complete?

    - by Robert
    Regular expressions are often pointed to as the classical example of a language that is not Turning complete. For example "regular expressions" is given in as the answer to this SO question looking for languages that are not Turing complete. In my, perhaps somewhat basic, understanding of the notion of Turning completeness, this means that regular expressions cannot be used check for patterns that are "balanced". Balanced meaning have an equal number of opening characters as closing characters. This is because to do this would require you to have some kind of state, to allow you to match the opening and closing characters. However the .NET implementation of regular expressions introduces the notion of a balanced group. This construct is designed to let you backtrack and see if a previous group was matched. This means that a .NET regular expressions: ^(?<p>a)*(?<-p>b)*(?(p)(?!))$ Could match a pattern that: ab aabb aaabbb aaaabbbb ... etc. ... Does this means .NET's regular expressions are Turing complete? Or are there other things that are missing that would be required for the language to be Turing complete?

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  • Approximate timings for various operations on a "typical desktop PC" anno 2010

    - by knorv
    In the article "Teach Yourself Programming in Ten Years" Peter Norvig (Director of Research, Google) gives the following approximate timings for various operations on a typical 1GHz PC back in 2001: execute single instruction = 1 nanosec = (1/1,000,000,000) sec fetch word from L1 cache memory = 2 nanosec fetch word from main memory = 10 nanosec fetch word from consecutive disk location = 200 nanosec fetch word from new disk location (seek) = 8,000,000 nanosec = 8 millisec What would the corresponding timings be for your definition of a typical PC desktop anno 2010?

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  • What is the best way to implement this composite GetHashCode()

    - by Frank Krueger
    I have a simple class: public class TileName { int Zoom, X, Y; public override bool Equals (object obj) { var o = obj as TileName; return (o != null) && (o.Zoom == Zoom) && (o.X == X) && (o.Y == Y); } public override int GetHashCode () { return (Zoom + X + Y).GetHashCode(); } } I was curious if I would get a better distribution of hash codes if I instead did something like: public override int GetHashCode () { return Zoom.GetHashCode() + X.GetHashCode() + Y.GetHashCode(); } This class is going to be used as a Dictionary key, so I do want to make sure there is a decent distribution.

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  • O(log N) == O(1) - Why not?

    - by phoku
    Whenever I consider algorithms/data structures I tend to replace the log(N) parts by constants. Oh, I know log(N) diverges - but does it matter in real world applications? log(infinity) < 100 for all practical purposes. I am really curious for real world examples where this doesn't hold. To clarify: I understand O(f(N)) I am curious about real world examples where the asymptotic behaviour matters more than the constants of the actual performance. If log(N) can be replaced by a constant it still can be replaced by a constant in O( N log N). This question is for the sake of (a) entertainment and (b) to gather arguments to use if I run (again) into a controversy about the performance of a design.

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  • Detecting Markers Using OpenCV

    - by Hamza Yerlikaya
    I am trying to detect various objects containing colored markers, so a red blue green marker identifies object A, and a red blue red marker identifies object B. My problem is I can't use template matching cause objects can be rotated, currently I am thinking about check for each color then find the object by checking the distance between colors but it seems inefficient, so my question is there a better way to do this?

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  • How to setup Ubuntu as a backup server for my Windows computer?

    - by derek
    I took my old computer (AMD 5600+, 2GB RAM, 880gt, 250GB SATA, etc) and decided to jump and try Ubuntu for the first time. I have very very little knowledge (Red Hat when I was younger) with Linux in general. My main desktop is Windows 7 and my plan is to use the Ubuntu computer as a file server sort of speak. I want to be able to setup back up schedules from my Windows PC to the Ubuntu PC (plan on leaving this on 24/7 to double as a Seedbox) How do I go on to doing this?

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  • PostgreSQL + Rails citext

    - by glebm
    I am trying to move to heroku which uses PostgreSQL 8.4 which has a citext column type which is nice since the app was written for MySQL. Is there any way to use :citext with rails (so that if the migrations are run on MySQL the citext would just use string/text? I found this ticket, but it seems like it isn't going to be a part of rails for a while: https://rails.lighthouseapp.com/projects/8994/tickets/3174-add-support-for-postgresql-citext-column-type

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  • sql count conditions

    - by user1311030
    there! I have this question, hope you guys can help me out. So i have this table with two fields: type and authorization in type i have 2 different values: Raid and Hold in authorization i have 2 different values: Accepted or Denied I need to make a view that returns values like this: TYPE:RAID ACCEPTED:5 DENIED:7 Basically i need to know how many of the values in TYPE are Raid, and then how many of them are Accepted and Denied. Thank you in advance!!

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  • how to merge file lines having the same first word in python?

    - by user1377135
    I have written a program to merge lines in a file containing the same first word in python. However I am unable to get the desired output. Can anyone please suggest me the mistake in my program? input "file.txt" line1: a b c line2: a b1 c1 line3: d e f line4: i j k line5: i s t line6: i m n ` output a b c a b1 c1 d e f i j k i s t i m n my code a = [line.split() for line in open('file.txt')] L=[] for i in range(0,len(a)): j=i while True: if a[j][0] == a[j+1][0]: L.append(a[j]) L.append(a[j+1]) j=j+2 else: print a[i] print L break

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  • Optimally place a pie slice in a rectangle.

    - by Lisa
    Given a rectangle (w, h) and a pie slice with start angle and end angle, how can I place the slice optimally in the rectangle so that it fills the room best (from an optical point of view, not mathematically speaking)? I'm currently placing the pie slice's center in the center of the rectangle and use the half of the smaller of both rectangle sides as the radius. This leaves plenty of room for certain configurations. Examples to make clear what I'm after, based on the precondition that the slice is drawn like a unit circle: A start angle of 0 and an end angle of PI would lead to a filled lower half of the rectangle and an empty upper half. A good solution here would be to move the center up by 1/4*h. A start angle of 0 and an end angle of PI/2 would lead to a filled bottom right quarter of the rectangle. A good solution here would be to move the center point to the top left of the rectangle and to set the radius to the smaller of both rectangle sides. This is fairly easy for the cases I've sketched but it becomes complicated when the start and end angles are arbitrary. I am searching for an algorithm which determines center of the slice and radius in a way that fills the rectangle best. Pseudo code would be great since I'm not a big mathematician.

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  • How to do motion tracking of a object using video

    - by Niroshan
    Could someone direct me to a tutorial or guide me how to track motion of a object moving with 6 DOF. I am planing to use a video stream of a moving toy car. I want to calculate displacement and rotation angle of the toy car. I came across some research papers but couldn't find any libraries to the job. Is there a way to do this using OpenCV or Matlab or some other freely available software? Thank you

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  • Determine an elements position in a variable length grid of elements

    - by gaoshan88
    I have a grid of a variable number of elements. Say 5 images per row and a variable number of images. I need to determine which column (for lack of a better word) each image is in... i.e. 1, 2, 3, 4 or 5. In this grid, images 1, 6, 12 and 17 would be in column 1 while 4, 9 and 15 would be in column 4. 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 What I am trying to do is apply a background image to each element based on it's column position. An example of this hard coded and inflexible (and if I'm barking up the wrong tree here by all means tell me how you'd ideally accomplish this as it always bugs me when I see someone ask "How do I build a gold plated, solar powered jet pack to get to the top of this building?" when they really should be asking "Where's the elevator?"): switch (imgnum){ case "1" : case "6" : case "11" : value = "1"; break; case "2" : case "7" : case "12" : value = "2"; break; case "3" : case "8" : case "13" : value = "3"; break; case "4" : case "9" : case "14" : value = "4"; break; case "5" : case "10" : case "15" : value = "5"; break; default : value = ""; } $('.someclass > ul').css('background','url("/img/'+value+'.png") no-repeat');

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  • How do I construct a 3D model of a room from 2 stereo cameras? What is the determining factor to an

    - by yasumi
    Currently, I have extracted depth points to construct a 3D model from 2 stereo cameras. The methods I have used are openCV graphCut method and a software from http://sourceforge.net/projects/reconststereo/. However, the generated 3D models are not very accurate, which leads me to question: 1) What is the problem with pixel-based method? 2) Should I change my pixel-based method to feature-based or object-recognition-based method? Is there a best method? 3) Are there any other ways to do such reconstruction? Additionally, the depth extracted comes only from 2 images. What if I am turning the camera 360 degrees to obtain a video? Looking forward to suggestion on how to combine this depth information. Thank you very much :)

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  • Is there a mean to specify specialization-genralization (inheritance) of actors in UML?

    - by Ivan
    I am just starting to use UML and have came to the following question: Some actors clearly are specialized versions of a natural entity. For example I've got Administrator and User actors which are clearly nothing but different roles of a user, Authorizer and Dispatcher which are services (and are going to be implemented this way). Should I just ignore these facts while modelling actors and use cases or specify it some way? I think I could make good use of such a specification to facilitate code generation.

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