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• Is it bad practice to pass instances through several layers?

  - by Puckl

  In my program design, I often come to the point where I have to pass object instances through several classes. For example, if I have a controller that loads an audio file, and then passes it to a player, and the player passes it to the playerRunnable, which passes it again somewhere else etc. It looks kind of bad, but I don´t know how to avoid it. Or is it OK to do this? EDIT: Maybe the player example is not the best because I could load the file later, but in other cases that does not work.

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• Is it a good idea to simplify an character -driven game engine to the point it's unnecessary to learn scripting/programming ?

  - by jokoon

  I remember, and I still think, that one cannot even make a prototyped 3D game to test just simple behaviors without using gigantic tools like unity or knowing extensive C++ programming, design pattern, a decent or basic 3D engine, etc. Now I'm wondering, since I know programming, that I'm still more lucky that the ones who need to learn programming prior to know how to make something: even scripted engines such as unity are not for kids, and to my sense they tend to dictate their ways of doing things, which is not the case with engine like ogre or irrlicht. I remember toying a little with the blender game engine, it was possible to link states or something I don't remember very well. Now I'm thinking that character driven games occupies a big part of the game market. Do you think it is a good idea to make a character-controlled oriented game engine which allows only to build AI instead of anything else ?

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• Earliest use of Comments as Semantically Meaningful Things in a Program?

  - by Alan Storm

  In certain corners of the PHP meta-programming world, it's become fashionable to use PHPDoc comments as a mechanism for providing semantically meaningful information to a program. That is, other code will parse the doc blocks and do something significant with the information encoded in those comments. Doctrine's annotations and code generation are an example of this. What's the earliest (or some early) use of this technique? I have vague memories of some early java Design by Contract implementations doing similar things, but I'm not sure of those folks were inventing the technique, or if they got it from somewhere. Mainly asking so I can provide some historical context for PHP developers who haven't come across the technique before, and are distrustful of it because it seems a little crazy pants.

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• Subscribe/Publish Model in Web-based Application (c#) - Best Practices for Event Handlers

  - by KingOfHypocrites

  I was recently exposed to a desktop application that uses an publish/subscribe model to handle commands, events, etc. I can't seem to find any good examples of using this in a web application, so I wonder if I am off base in trying to use this for web based development (on the server side)? I'm using asp.net c#. My main question in regards to the design is: When using a publish/subscribe model, is it better to have generic commands/events that pass no parameters and then have the subscribers look at static context objects that contain the data relevant to the event? Or is it better to create custom arguments for every event that contain data related to the event? The whole concept of a global container seems so convenient but at the same time seems to break encapsulation. Any thoughts or best practices from anyone who has implemented this type of model in a web based application? Even suggestions on this model out of the scope of my question are appreciated.

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• How to change the state of a singleton in runtime

  - by user34401

  Consider I am going to write a simple file based logger AppLogger to be used in my apps, ideally it should be a singleton so I can call it via public class AppLogger { public static String file = ".."; public void logToFile() { // Write to file } public static log(String s) { AppLogger.getInstance().logToFile(s); } } And to use it AppLogger::log("This is a log statement"); The problem is, what is the best time I should provide the value of file since it is a just a singleton? Or how to refactor the above code (or skip using singleton) so I can customize the log file path? (Assume I don't need to write to multiple at the same time) p.s. I know I can use library e.g. log4j, but consider it is just a design question, how to refactor the code above?

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• Event Aggregator.. not getting a response, how to determine completion?

  - by Duncan_m

  I'm rewriting a vehicle tracking application, a google maps based thing.. The users are able to search for a vehicle by typing a few characters of the vehicles "callsign". My application is based around a sort of "event bus" within Backbone.. when a search occurs I send a message on the bus saying something like "does anyone match this?".. If a marker matches the search term it responds with a sort of "yes, I match!".. My challenge arises when no-one matches, I get no response.. it feels a little hacky to "wait a little while" and check if a response has been recieved.. The application is based around Backbone.js and using the Event Aggregator pattern described in the answer to this question on Stack Overflow: http://stackoverflow.com/questions/7708195/access-function-in-one-view-from-another-in-backbone-js Is there a well defined design pattern that might assist me here? Sending a request for a response and not getting any responses?

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• When designing an application around Model-View-Controller (MVC), what is in your toolbox?

  - by ericgorr

  There are a lot of great explanations for what the Model-View-Controller design pattern is, but I am having trouble finding good resources showing how to use it in practice. So, when you are starting a new application (doesn't matter what it is), what is in your toolbox? For example, it was suggested that using UML collaboration diagrams ( http://www.objectmentor.com/resources/articles/umlCollaborationDiagrams.pdf ) can be useful when designing an application around MVC, although, I am not certain exactly how or why this might be the case...? So, what is in your toolbox for MVC?

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• Distinguishing between sets of status reports

  - by user1769486

  I am working on an internal database monitoring system and am at a point where I sort of hit the wall in terms of application design. Basically I have an extensible plugin architecture where I shall have an OK, a warning or an error upon running a db verification. My first question whether it is sufficient to have only one status reported with an optional status message or provide the ability to have more than one returned (with attached messages) and then calculate an aggregated overall status. In particular in the latter case my second issue would be how to distinguish between two verification reports with the same status code (as it can come from different triggers). I would need to do this to see whether some change happened between the current and last verification. I could simply have string comparisons of the attached status messages mentioned above but that does not seem very reliable.

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• Wrappers/law of demeter seems to be an anti-pattern...

  - by Robert Fraser

  I've been reading up on this "Law of Demeter" thing, and it (and pure "wrapper" classes in general) seem to generally be anti patterns. Consider an implementation class: class Foo { void doSomething() { /* whatever */ } } Now consider two different implementations of another class: class Bar1 { private static Foo _foo = new Foo(); public static Foo getFoo() { return _foo; } } class Bar2 { private static Foo _foo = new Foo(); public static void doSomething() { _foo.doSomething(); } } And the ways to call said methods: callingMethod() { Bar1.getFoo().doSomething(); // Version 1 Bar2.doSomething(); // Version 2 } At first blush, version 1 seems a bit simpler, and follows the "rule of Demeter", hide Foo's implementation, etc, etc. But this ties any changes in Foo to Bar. For example, if a parameter is added to doSomething, then we have: class Foo { void doSomething(int x) { /* whatever */ } } class Bar1 { private static Foo _foo = new Foo(); public static Foo getFoo() { return _foo; } } class Bar2 { private static Foo _foo = new Foo(); public static void doSomething(int x) { _foo.doSomething(x); } } callingMethod() { Bar1.getFoo().doSomething(5); // Version 1 Bar2.doSomething(5); // Version 2 } In both versions, Foo and callingMethod need to be changed, but in Version 2, Bar also needs to be changed. Can someone explain the advantage of having a wrapper/facade (with the exception of adapters or wrapping an external API or exposing an internal one).

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• dynamic behavior of factory class

  - by manu1001

  I have a factory class that serves out a bunch of properties. Now, the properties might come either from a database or from a properties file. This is what I've come up with. public class Factory { private static final INSTANCE = new Factory(source); private Factory(DbSource source) { // read from db, save properties } private Factory(FileSource source) { // read from file, save properties } // getInstance() and getProperties() here } What's a clean way of switching between these behaviors based on the environment. I want to avoid having to recompile the class each time.

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• QuestionOrAnswer model?

  - by Mark

  My site has Listings. Users can ask Questions about listings, and the author of the listing can respond with an Answer. However, the Answer might need clarification, so I've made them recursive (you can "answer" an answer). So how do I set up the database? The way I have it now looks like this (in Django-style models): class QuestionOrAnswer(Model): user = ForeignKey(User, related_name='questions') listing = ForeignKey(Listing, related_name='questions') parent = models.ForeignKey('self', null=True, blank=True, related_name='children') message = TextField() But what bugs me is that listing is now an attribute of the answers as well (it doesn't need to be). What happens if the database gets mangled and an answer belongs to a different listing than its parent question? That just doesn't make any sense. We can separate it with polymorphism: QuestionOrAnswer user message created updated Question(QuestionOrAnswer) shipment Answer(QuestionOrAnswer) parent = ForeignKey(QuestionOrAnswer) And that ought to work, but now ever question and answer is split into 2 tables. Is it worth this overhead for clearly defined models?

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• Help naming a class that has a single public method called Execute()

  - by devoured elysium

  I have designed the following class that should work kind of like a method (usually the user will just run Execute()): public abstract class ??? { protected bool hasFailed = false; protected bool hasRun = false; public bool HasFailed { get { return hasFailed; } } public bool HasRun { get { return hasRun; } } private void Restart() { hasFailed = false; hasRun = false; } public bool Execute() { ExecuteImplementation(); bool returnValue = hasFailed; Restart(); return returnValue; } protected abstract void ExecuteImplementation(); } My question is: how should I name this class? Runnable? Method(sounds awkward)?

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• Minimize useless tweaking of a numeric app

  - by Potatoswatter

  I'm developing a numeric application (nonlinear optimizer), with a zillion knobs to tweak and rising. It's not my first foray into this domain, but this time there are even more variables in the code and I'm on a tight schedule. Don't want to waste time fiddling. Days or even months can potentially be wasted adjusting variables, recompiling, and reprocessing benchmark datasets. The resulting data is viewed and trouble spots are checked. The overall quality of the solution is reported by the program but the meaning of the report could change over time. (Numeric units for the report are one thing I'm trying to nail down.) One main problem is organizing result files to identify each with specific code changes. Note taking can be a pain, is there software to help with this? Are there agreed best practices to making this kind of development cycle reliably move forward? The solver package converges to its optimal solution with mechanical determination, but I'm all too familiar with the way an excess of design decisions can mire development.

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• Prioritize compiler functionality/tasks, when designing a new language

  - by Mahdi

  Well, the question should be so hard to ask and I expect couple of down votes, however, I'm really interested to have your ideas and recommendations. :) I've already made a very simple compiler, with a few and limited functionality. Now I'm getting more on it to make it more like a real-world compiler. I definitely need to start over 'cause I've much more experience and ideas in this area rather a few years ago. So, I want to know, right now, from the very first step again, which tasks/features for the new compiler should implement first and which tasks has lower priority rather than others? For example, I'd say, first I'd go to decide about the object-oriented structure for the new language, but you might say, hey, just go for a compiler that could define a variable, when you finished that, then start thinking about OOP designs ... I prefer to hear the pros and cons for your suggestions also. Actually I like to start from Bottom to Top, where I could add simplest tasks first, and later adding more complex ones, but I'm totally open for any new ideas, and really appreciate that. Also please consider that I'm thinking about the design concepts. Actually I expect answers like: Priority from Highest to Lowest: variables, because .... functions, because .... loops, because .... ... Not: define a syntax for your new language, and start parsing your source code ...

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• Struggling with the Single Responsibility Principle

  - by AngryBird

  Consider this example: I have a website. It allows users to make posts (can be anything) and add tags that describe the post. In the code, I have two classes that represent the post and tags. Lets call these classes Post and Tag. Post takes care of creating posts, deleting posts, updating posts, etc. Tag takes care of creating tags, deleting tags, updating tags, etc. There is one operation that is missing. The linking of tags to posts. I am struggling with who should do this operation. It could fit equally well in either class. On one hand, the Post class could have a function that takes a Tag as a parameter, and then stores it in a list of tags. On the other hand, the Tag class could have a function that takes a Post as a parameter and links the Tag to the Post. The above is just an example of my problem. I am actually running into this with multiple classes that are all similar. It could fit equally well in both. Short of actually putting the functionality in both classes, what conventions or design styles exist to help me solve this problem. I am assuming there has to be something short of just picking one? Maybe putting it in both classes is the correct answer?

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• From a DDD perspective is a report generating service a domain service or an infrastructure service?

  - by Songo

  Let assume we have the following service whose responsibility is to generate Excel reports: class ExcelReportService{ public String generateReport(String fileFormatFilePath, ResultSet data){ ReportFormat reportFormat = new ReportFormat(fileFormatFilePath); ExcelDataFormatterService excelDataFormatterService = new ExcelDataFormatterService(); FormattedData formattedData = excelDataFormatterService.format(data); ExcelFileService excelFileService = new ExcelFileService(); String reportPath= excelFileService.generateReport(reportFormat,formattedData); return reportPath; } } This is pseudo code for the service I want to design where: fileFormatFilePath: path to a configuration file where I'll keep the format of my excel file (headers, column widths, number of columns,..etc) data: the actual records returned from the database. This data can't be used directly coz I might need to make further calculations to the data before inserting them to the excel file. ReportFormat: Value object to hold the report format, has methods like getHeaders(), getColumnWidth(),...etc. ExcelDataFormatterService: a service to hold any logic that need to be applied to the data returned from the database before inserting it to the file. FormattedData: Value object the represents the formatted data to be inserted. ExcelFileService: a wrapper top the 3rd party library that generates the excel file. Now how do you determine whether a service is an infrastructure or domain service? I have the following 3 services here: ExcelReportService, ExcelDataFormatterService and ExcelFileService?

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• Implementing a ILogger interface to log data

  - by Jon

  I have a need to write data to file in one of my classes. Obviously I will pass an interface into my class to decouple it. I was thinking this interface will be used for testing and also in other projects. This is my interface: //This could be used by filesystem, webservice public interface ILogger { List<string> PreviousLogRecords {get;set;} void Log(string Data); } public interface IFileLogger : ILogger { string FilePath; bool ValidFileName; } public class MyClassUnderTest { public MyClassUnderTest(IFileLogger logger) {....} } [Test] public void TestLogger() { var mock = new Mock<IFileLogger>(); mock.Setup(x => x.Log(Is.Any<string>).AddsDataToList()); //Is this possible?? var myClass = new MyClassUnderTest(mock.Object); myClass.DoSomethingThatWillSplitThisAndLog3Times("1,2,3"); Assert.AreEqual(3,mock.PreviousLogRecords.Count); } This won't work I don't believe as nothing is storing the items so is this possible using Moq and also what do you think of the design of the interface?

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• Parameterized Django models

  - by mgibsonbr

  In principle, a single Django application can be reused in two or more projects, providing functionality relevent to both. That implies that the same database structure (tables and relations) will be re-created identically in different databases, and most times this is not a problem (assuming the projects/databases are unrelated - for instance when someone downloads a complete app to use in their own projects). Sometimes, however, the models must be "tweaked" a little to better fit the problem needs. This can be accomplished by forking the app, but I wondered if there wouldn't be a better option in cases where the app designer can anticipate the most common customizations. For instance, if I have a model that could relate to another as one-to-one or one-to-many, I could specify the unique property as a parameter, that can be specified in the project's settings: class This(models.Model): other = models.ForeignKey(Other, unique=settings.OTHER_TO_THIS) Or if a model can relate to many others, I could create an intermediate table for each of them (thus enforcing referential integrity) instead of using generic fks: for related in settings.MODELS_RELATED_TO_OTHER: model_name = '%s_Other' % related globals()[model_name] = type(model_name, (models.Model,) { me:models.ForeignKey(find_model_class(related)), other:models.ForeignKey(Other), # Some other properties all intersection tables must have }) Etc. Let me stress out that I'm not proposing to change the models at runtime nor anything like that; once the parameters were defined and syncdb called for the first time, those parameters are not to be changed again (unless you're doing a schema migration). Is this a good design? Are there better ways to accomplish the same thing, or maybe drawbacks I coulnd't anticipate? This technique is meant to be used sparingly (only on apps meant to be reused in wildly different contexts, and only when a specific need of customization can be detected while the app model is being designed).

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• Handling Types for Real and Complex Matrices in a BLAS Wrapper

  - by mga

  I come from a C background and I'm now learning OOP with C++. As an exercise (so please don't just say "this already exists"), I want to implement a wrapper for BLAS that will let the user write matrix algebra in an intuitive way (e.g. similar to MATLAB) e.g.: A = B*C*D.Inverse() + E.Transpose(); My problem is how to go about dealing with real (R) and complex (C) matrices, because of C++'s "curse" of letting you do the same thing in N different ways. I do have a clear idea of what it should look like to the user: s/he should be able to define the two separately, but operations would return a type depending on the types of the operands (R*R = R, C*C = C, R*C = C*R = C). Additionally R can be cast into C and vice versa (just by setting the imaginary parts to 0). I have considered the following options: As a real number is a special case of a complex number, inherit CMatrix from RMatrix. I quickly dismissed this as the two would have to return different types for the same getter function. Inherit RMatrix and CMatrix from Matrix. However, I can't really think of any common code that would go into Matrix (because of the different return types). Templates. Declare Matrix<T> and declare the getter function as T Get(int i, int j), and operator functions as Matrix *(Matrix RHS). Then specialize Matrix<double> and Matrix<complex>, and overload the functions. Then I couldn't really see what I would gain with templates, so why not just define RMatrix and CMatrix separately from each other, and then overload functions as necessary? Although this last option makes sense to me, there's an annoying voice inside my head saying this is not elegant, because the two are clearly related. Perhaps I'm missing an appropriate design pattern? So I guess what I'm looking for is either absolution for doing this, or advice on how to do better.

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• Best practice to collect information from child objects

  - by Markus

  I'm regularly seeing the following pattern: public abstract class BaseItem { BaseItem[] children; // ... public void DoSomethingWithStuff() { StuffCollection collection = new StuffCollection(); foreach(child c : children) c.AddRequiredStuff(collection); // do something with the collection ... } public abstract void AddRequiredStuff(StuffCollection collection); } public class ConcreteItem : BaseItem { // ... public override void AddRequiredStuff(StuffCollection collection) { Stuff stuff; // ... collection.Add(stuff); } } Where I would use something like this, for better information hiding: public abstract class BaseItem { BaseItem[] children; // ... public void DoSomethingWithStuff() { StuffCollection collection = new StuffCollection(); foreach(child c : children) collection.AddRange(c.RequiredStuff()); // do something with the collection ... } public abstract StuffCollection RequiredStuff(); } public class ConcreteItem : BaseItem { // ... public override StuffCollection RequiredStuff() { StuffCollection stuffCollection; Stuff stuff; // ... stuffCollection.Add(stuff); return stuffCollection; } } What are pros and cons of each solution? For me, giving the implementation access to parent's information is some how disconcerting. On the other hand, initializing a new list, just to collect the items is a useless overhead ... What is the better design? How would it change, if DoSomethingWithStuff wouldn't be part of BaseItem but a third class? PS: there might be missing semicolons, or typos; sorry for that! The above code is not meant to be executed, but just for illustration.

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• Classes as a compilation unit

  - by Yannbane

  If "compilation unit" is unclear, please refer to this. However, what I mean by it will be clear from the context. Edit: my language allows for multiple inheritance, unlike Java. I've started designing+developing my own programming language for educational, recreational, and potentially useful purposes. At first, I've decided to base it off Java. This implied that I would have all the code be written inside classes, and that code compiles to classes, which are loaded by the VM. However, I've excluded features such as interfaces and abstract classes, because I found no need for them. They seemed to be enforcing a paradigm, and I'd like my language not to do that. I wanted to keep the classes as the compilation unit though, because it seemed convenient to implement, familiar, and I just liked the idea. Then I noticed that I'm basically left with a glorified module system, where classes could be used either as "namespaces", providing constants and functions using the static directive, or as templates for objects that need to be instantiated ("actual" purpose of classes in other languages). Now I'm left wondering: what are the benefits of having classes as compilation units? (Also, any general commentary on my design would be much appreciated.)

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• DB Object passing between classes singleton, static or other?

  - by Stephen

  So I'm designing a reporting system at work it's my first project written OOP and I'm stuck on the design choice for the DB class. Obviously I only want to create one instance of the DB class per-session/user and then pass it to each of the classes that need it. What I don't know it what's best practice for implementing this. Currently I have code like the following:- class db { private $user = 'USER'; private $pass = 'PASS'; private $tables = array( 'user','report', 'etc...'); function __construct(){ //SET UP CONNECTION AND TABLES } }; class report{ function __construct ($params = array(), $db, $user) { //Error checking/handling trimed //$db is the database object we created $this->db = $db; //$this->user is the user object for the logged in user $this->user = $user; $this->reportCreate(); } public function setPermission($permissionId = 1) { //Note the $this->db is this the best practise solution? $this->db->permission->find($permissionId) //Note the $this->user is this the best practise solution? $this->user->checkPermission(1) $data=array(); $this->db->reportpermission->insert($data) } };//end report I've been reading about using static classes and have just come across Singletons (though these appear to be passé already?) so what's current best practice for doing this?

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• Tips for Making this Code Testable [migrated]

  - by Jesse Bunch

  So I'm writing an abstraction layer that wraps a telephony RESTful service for sending text messages and making phone calls. I should build this in such a way that the low-level provider, in this case Twilio, can be easily swapped without having to re-code the higher level interactions. I'm using a package that is pre-built for Twilio and so I'm thinking that I need to create a wrapper interface to standardize the interaction between the Twilio service package and my application. Let us pretend that I cannot modify this pre-built package. Here is what I have so far (in PHP): <?php namespace Telephony; class Provider_Twilio implements Provider_Interface { public function send_sms(Provider_Request_SMS $request) { if (!$request->is_valid()) throw new Provider_Exception_InvalidRequest(); $sms = \Twilio\Twilio::request('SmsMessage'); $response = $sms->create(array( 'To' => $request->to, 'From' => $request->from, 'Body' => $request->body )); if ($this->_did_request_fail($response)) { throw new Provider_Exception_RequestFailed($response->message); } $response = new Provider_Response_SMS(TRUE); return $response; } private function _did_request_fail($api_response) { return isset($api_response->status); } } So the idea is that I can write another file like this for any other telephony service provided that it implements Provider_Interface making them swappable. Here are my questions: First off, do you think this is a good design? How could it be improved? Second, I'm having a hard time testing this because I need to mock out the Twilio package so that I'm not actually depending on Twilio's API for my tests to pass or fail. Do you see any strategy for mocking this out? Thanks in advance for any advice!

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• 7 Web Design Tutorials from PSD to HTML/CSS

  - by Sushaantu

  Some time back when I was looking for some tutorials to create a website from scratch i.e. the process from designing the PSD to slice it and CSS/XHTML it, then not many quality results appeared. But that was like almost an year back and a lot of water has flown down the river Thanes since then. In this list I will give you links to some wonderful tutorials teaching you in a step by step way to design a website. These tutorials are ideal for someone who is learning web designing and has grasp of basic CSS, XHTML and little designing on Photoshop. How to Design and Code Web 2.0 Style Web Design Design a website from PSD to HTML Designing and Coding a Grunge Web Design from Scratch Creating a CSS layout from scratch Build a Sleek Portfolio Site from Scratch Designing and Coding a web design from scratch Design and Code a Dark and Sleek Web Design

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• Mission 26 Captures Endeavour’s Last Trip in Stop Motion

  - by Jason Fitzpatrick

  On September 21, 2012 the Space Shuttle Endeavour was delivered to the Los Angeles International Airport and spent the next three days being slowly transported 12 miles to the California Science Center. One dedicated team of photographers captured the whole thing. Lead by Matthew Givot, the group followed the shuttle for three straight days, photographing it around the clock. The Endeavor started on Thursday night and went on until Sunday night, with very little sleep to no sleep. The only thing that kept us going was pure love of the art and adrenaline. One thing that stood out the most for me, while I was shooting, was the people of Los Angeles. It was so powerful to see the excitement on peoples faces and the pride of their home town. No matter how many times I would see the Shuttle it would never get old. This has been an amazing experience that I will never forget. My hope is that this film will show you the amount of dedicated people and teamwork that it took to get the Endeavour to its new home. Enjoy. The end result of their labor is the above video, a beautiful time-lapse video of Endeavour’s journey from the airport to its hanger at the California Science Center. Can Dust Actually Damage My Computer? What To Do If You Get a Virus on Your Computer Why Enabling “Do Not Track” Doesn’t Stop You From Being Tracked

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