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• How to use R-Tree for plotting large number of map markers on google maps

  - by Eeyore

  After searching SO and multiple articles I haven't found a solution to my problem. What I am trying to achieve is to load 20,000 markers on Google Maps. R-Tree seems like a good approach but it's only helpful when searching for points within the visible part of the map. When the map is zoomed out it will return all of the points and...crash the browser. There is also the problem with dragging the map and at the end of dragging re-running the query. I would like to know how I can use R-Tree and be able to achieve the all of the above.

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• Calculating rotation and translation matrices between two odometry positions for monocular linear triangulation

  - by user1298891

  Recently I've been trying to implement a system to identify and triangulate the 3D position of an object in a robotic system. The general outline of the process goes as follows: Identify the object using SURF matching, from a set of "training" images to the actual live feed from the camera Move/rotate the robot a certain amount Identify the object using SURF again in this new view Now I have: a set of corresponding 2D points (same object from the two different views), two odometry locations (position + orientation), and camera intrinsics (focal length, principal point, etc.) since it's been calibrated beforehand, so I should be able to create the 2 projection matrices and triangulate using a basic linear triangulation method as in Hartley & Zissermann's book Multiple View Geometry, pg. 312. Solve the AX = 0 equation for each of the corresponding 2D points, then take the average In practice, the triangulation only works when there's almost no change in rotation; if the robot even rotates a slight bit while moving (due to e.g. wheel slippage) then the estimate is way off. This also applies for simulation. Since I can only post two hyperlinks, here's a link to a page with images from the simulation (on the map, the red square is simulated robot position and orientation, and the yellow square is estimated position of the object using linear triangulation.) So you can see that the estimate is thrown way off even by a little rotation, as in Position 2 on that page (that was 15 degrees; if I rotate it any more then the estimate is completely off the map), even in a simulated environment where a perfect calibration matrix is known. In a real environment when I actually move around with the robot, it's worse. There aren't any problems with obtaining point correspondences, nor with actually solving the AX = 0 equation once I compute the A matrix, so I figure it probably has to do with how I'm setting up the two camera projection matrices, specifically how I'm calculating the translation and rotation matrices from the position/orientation info I have relative to the world frame. How I'm doing that right now is: Rotation matrix is composed by creating a 1x3 matrix [0, (change in orientation angle), 0] and then converting that to a 3x3 one using OpenCV's Rodrigues function Translation matrix is composed by rotating the two points (start angle) degrees and then subtracting the final position from the initial position, in order to get the robot's straight and lateral movement relative to its starting orientation Which results in the first projection matrix being K [I | 0] and the second being K [R | T], with R and T calculated as described above. Is there anything I'm doing really wrong here? Or could it possibly be some other problem? Any help would be greatly appreciated.

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• resetting the image in an NSView

  - by Josan

  I think this is a very simple question, but I’m new to programming so I may be going about it in a wrong-headed way. I have a basic understanding of Objective-C writing terminal applications and am teaching myself how to use the Cocoa GUI. I understand how to use IBOutlet and IBAction to connect a simple button to a method that will repeatedly send random numbers to a textfield . I understand how to add a NSView file, connect it to a custom view in interface builder and draw a path through random points in the view when the application launches. (I’ve been putting this code inside the - (void)drawRect:(NSRect)dirtyRect method that is declared when the file is created). What I can’t seem to figure out is how to connect a button to an action that will then ‘refresh’ the view – in this case repopulate it with another set of random points connected with a path. Looking at the documentation, I think I should somehow be using – (void) setNeedsDisplay(BOOL)flag but nothing I have tried so far had worked. Please tell me, what am I missing here?

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• How to automate the finding of an M value along a route

  - by Heather Taylor

  Kirk Kuykendall had given a script example a few years back in an ESRI forum http://forums.esri.com/Thread.asp?c=93&f=996&t=88246&mc=4 as to how to find the M (measure) value of a point in a shapefile along a route when you clicked on the point. This is very handy, BUT..I have 1500 points that I need M values for. Is there a way to automate this type of thing? I need the M values for the points to create linear events on the route. Note: I am not a programmer, but have people who can help me out.

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• Can't draw to a pictureBox in a loop

  - by Jason94

  I have a List<Point> where Point contains X and Y. What i want is to loop a list like that and draw a line point to point, i do so by: foreach (List<Point> wps in map.waypoints) { System.Drawing.Pen myPen; myPen = new System.Drawing.Pen(System.Drawing.Color.Black); System.Drawing.Graphics formGraphics = this.pictureBox1.CreateGraphics(); Point startPos = new Point(wps[0].X, wps[0].Y); foreach (Point p in wps) { formGraphics.DrawLine(myPen, startPos.X, startPos.Y, p.X, p.Y); startPos = p; } myPen.Dispose(); formGraphics.Dispose(); } BUT nothing gets drawn! I did the same with the on_click event to the pictureBox but instead if a looping some Points ive just used mouse X and Y. I have verified the lists of points that they dont contain rubish :D

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• The use of GROUP BY in MySQL

  - by Gustav Bertram

  I'm fishing for a comprehensive and canonical answer for the typical "mysql group by?" question. Here is some sample data: TABLE A +------+------+----------+-----+ | id | foo | bar | baz | +------+------+----------+-----+ | 1 | 1 | hello | 42 | | 2 | 0 | apple | 96 | | 3 | 20 | boot | 11 | | 4 | 31 | unicorn | 99 | | 5 | 19 | pumpkin | 11 | | 6 | 88 | orange | 13 | +------+------+----------+-----+ TABLE B +------+------+ | id | moo | +------+------+ | 1 | 1 | | 2 | 99 | | 3 | 11 | +------+------+ Demonstrate and explain the correct use of the GROUP BY clause in MySQL. Touch upon the following points: The use of MIN, MAX, SUM, AVG The use of HAVING Grouping by date, and ranges of dates Grouping with an ORDER BY Grouping with a JOIN Grouping on multiple columns Bonus points for references to other great answers, the MySQL online manual, and online tutorials on GROUP BY.

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• Changing ylim (axis limits) drops data falling outside range. How can this be prevented?

  - by Alex Holcombe

  df <- data.frame(age=c(10,10,20,20,25,25,25),veg=c(0,1,0,1,1,0,1)) g=ggplot(data=df,aes(x=age,y=veg)) g=g+stat_summary(fun.y=mean,geom="point") Points reflect mean of veg at each age, which is what I expected and want to preserve after changing axis limits with the command below. g=g+ylim(0.2,1) Changing axis limits with the above command unfortunately causes veg==0 subset to be dropped from the data, yielding "Warning message: Removed 4 rows containing missing values (stat_summary)" This is bad because now the data plot (stat_summary mean) omits the veg==0 points. How can this be prevented? I simply want to avoid showing the empty part of the plot- the ordinate from 0 to .2, but not drop the associated data from the stat_summary calculation.

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• Directions and Route in iPhone using Bing Map

  - by sagargeo

  Can we load a Bing Map in iPhone and show Route between source and destination points thourgh some waypoints.

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• IIS not serving up .dat files.

  - by Stu

  Hi all, I have a ASP MVC web application that uses a plugin to load images and points for a 3d application. When debugging with the the Visual Studio development server the images and the points are served up great... http://i148.photobucket.com/albums/s19/littleniv/Debugging/local.png Second image: same url but iis.png When running in IIS 7 though the .Dat point files do not serve and produce a 404. I've noticed the caching is marked as private in fiddler, but i don't know what this means. Can anyone help? Cheers, Stu

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• JQuery slideToggle replace image src

  - by Rob

  Hi, This function is called when an up/down arrow is clicked to slide hidden div. If the div is hidden, the arrow points down and changes to up when the div is shown. If the div is shown, the arrow points up to hide div and changes to down when the div is closed. I just wanted to know if there was a more efficient way of doing this or if this is the correct way. Thanks. function showInfo(info_id) { var img_id = '#arrow_'+info_id; var div = '#info_'+appointment_id; $(div).slideToggle('normal',function() { if ($(this).is(':visible')) { $(img_id).attr('src',$(img_id).attr('src').replace('_down','_up')); } else { $(img_id).attr('src',$(img_id).attr('src').replace('_up','_down')); } });}

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• Changeing scaling of Matlab Figure

  - by Phil

  Hi, I have a figure that displays 20.000 points on the x-axis. So it labels the x-axis from 0 .. 20.000. However, now I would like to scale it form 0 to 50. But when I try to do this in the plot window it just shows me the first 50 points, instead of changeing the scale. Is there any straightforward way to do that in Matlab? Many thanks for your help!

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• Storing CLLocationCoordinates2D in NSMutableArray

  - by Amarsh

  After some searching, I got the following solution : ref: http://stackoverflow.com/questions/1392909/nsmutablearray-addobject-with-mallocd-struct CLLocationCoordinate2D* new_coordinate = malloc(sizeof(CLLocationCoordinate2D)); new_coordinate->latitude = latitude; new_coordinate->longitude = longitude; [points addObject:[NSData dataWithBytes:(void *)new_coordinate length:sizeof(CLLocationCoordinate2D)]]; free(new_coordinate); And access it as: CLLocationCoordinate2D* c = (CLLocationCoordinate2D*) [[points objectAtIndex:0] bytes]; However, someone claims that there is a memory leak here? Can anyone suggest me where is the leak and how to fix it. Further, is there a better way of storing a list of CLLocationCoordinate2D in NSMutableArray? Please give sample code since I am an Objective C newbie.

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• Rewriting a simple Pygame 2D drawing function in C++

  - by Dominic Bou-Samra

  I have a 2D list of vectors (say 20x20 / 400 points) and I am drawing these points on a screen like so: for row in grid: for point in row: pygame.draw.circle(window, white, (particle.x, particle.y), 2, 0) pygame.display.flip() #redraw the screen This works perfectly, however it's much slower then I expected. I want to rewrite this in C++ and hopefully learn some stuff (I am doing a unit on C++ atm, so it'll help) on the way. What's the easiest way to approach this? I have looked at Direct X, and have so far followed a bunch of tutorials and have drawn some rudimentary triangles. However I can't find a simple (draw point).

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• How can a Delphi TPersistent object calculate its own deserialization time?

  - by mjustin

  For performance tests I need a way to measure the time needed for a form to load its definition from the DFM. All existing forms inherit a custom form class. To capture the current time, this base class needs overriden methods as "extension points": start of the deserialization process after the deserialization (can be implemented by overriding the Loaded procedure) the moment just before the execution of the OnFormCreate event So the log for TMyForm.Create(nil) could look like: - 00.000 instance created - 00.010 before deserialization - 01.823 after deserialization - 02.340 before OnFormCreate Which TObject (or TComponent) methods are best suited? Maybe there are other extension points in the form creation process, please feel free to make suggestions.

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• How to discard time intervals with Time Series / XYPlots using JFreeChart?

  - by Alex Arnon

  Hi All, I am building a set of chart displays, one of which is for a month display of daily trading - that is, one point of data per day (closing). Since there is no trade during weekends and holidays, I need to discard these data points. Not only that, but data points should still appear adjacent to each other, regardless of any gaps in time. This can be seen in any such chart e.g. in the 3 month graph for Nasdaq on Yahoo Finance - see how weekends are skipped. My question is: how should one correctly implement this in JFreeChart? Thanks in advance!

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• iOS: How to access the `UIKeyboard`?

  - by MattDiPasquale

  I want to get a pointer reference to UIKeyboard *keyboard to the keyboard on screen so that I can add a transparent subview to it, covering it completely, to achieve the effect of disabling the UIKeyboard without hiding it. In doing this, can I assume that there's only one UIKeyboard on the screen at a time? I.e., is it a singleton? Where's the method [UIKeyboard sharedInstance]. Brownie points if you implement that method via a category. Or, even more brownie points if you convince me why it's a bad idea to assume only one keyboard and give me a better solution.

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• AspectJ join point with simple types

  - by Jon

  Hi! Are there defined join points in arithmetics that I can catch? Something like: int a = 4; int b = 2; int c = a + b; Can I make a pointcut that catches any one of those lines? And what context will I be able to get? I would like to add a before() to all int/float/double manipulation done in a particular method on a class, is that possible. I see in the AspectJ docs that there are defined join points for object initialization and method calls. Is declaring an int an object initialization and does the + operator count as a method call? Thanks!

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• How can I measure TForm deserialization time in Delphi?

  - by mjustin

  For performance tests I need a way to measure the time needed for a form to load its definition from the DFM. All existing forms inherit a custom form class. To capture the current time, this base class needs overriden methods as "extension points": before the beginning of the deserialization process after the completion of deserialization (can be implemented by overriding the Loaded procedure) the moment just before the execution of the OnFormCreate event Which TObject (or TComponent) methods are best suited? Maybe there are other extension points in the form creation process, please feel free to make suggestions.

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• Characteristics of an Initialization Vector

  - by Jamie Chapman

  I'm by no means a cryptography expert, I have been reading a few questions around Stack Overflow and on Wikipedia but nothing is really 'clear cut' in terms of defining an IV and it's usage. Points I have discovered: An IV is pre-pended to a plaintext message in order to strengthen the encryption The IV is truely random Each message has it's own unique IV Timestamps and cryptographic hashes are sometimes used instead of random values, but these are considered to be insecure as timestamps can be predicted One of the weaknesses of WEP (in 802.11) is the fact that the IV will reset after a specific amount of encryptions, thus repeating the IV I'm sure there are many other points to be made, what have I missed? (or misread!)

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• Counting distinct and duplicate attribute values in an array

  - by keruilin

  I have an array of users that's sorted in descending order based on total_points. I need to find the rank of each user in that array. The issue is that more than one user can have the same total points and, thus, the same rank. For example, three users could be in 3rd place with 200 Points. Here's my current code: class Leader < ActiveRecord::Base def self.points_leaders all_leaders = all_points_leaders # returns array of users sorted by total_points in desc order all_leaders_with_rank = [] all_leaders.each do |user| rank = all_leaders.index(user)+1 all_leaders_with_rank << Ldr.new(rank, user) # Ldr is a Struct end return all_leaders_with_rank end end How must I modify the code so that the correct rank is returned, and not just the value of the index position?

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• Shortest distance between two line segments

  - by Frank

  I need a function to find the shortest distance between two line segments. A line segment is defined by two endpoints. So for example one of my line segments (AB) would be defined by the two points A (x1,y1) and B (x2,y2) and the other (CD) would be defined by the two points C (x1,y1) and D (x2,y2). Feel free to write the solution in any language you want and I can translate it into javascript. Please keep in mind my geometry skills are pretty rusty. I have already seen http://stochastix.wordpress.com/2008/12/28/distance-between-two-lines/ and I am not sure how to translate this into a function. Thank you so much for help.

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• 3D line plane intersection, with simple plane

  - by clamp

  hello, i have two points in 3D space which have X-coordinates with different signum. so one of them lies definitely on one side of the X-plane and one on the other. now i want to find the intersection of this plane and the line made up by the two points in the most simple and optimized way. i know how to do general line plane intersection, but since in this case the plane is just the x-plane, i think there should be some shortcuts i can take. thanks!

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• Table alias -- Unkown column in field list

  - by Jason

  Hi all, I have a sql query which is executing a LEFT JOIN on 2 tables in which some of the columns are ambiguous. I can prefix the joined tables but when I try to prefix one of the columns from the table in the FROM clause, it tells me Unknown column. I even tried giving that table an alias like so ...From points AS p and using "p" to prefix the tables but that didn't work either. Can someone tell me what I'm doing wrong. Here is my query: SELECT point_title, point_url, address, city, state, zip_code, phone, `points`.`lat`, `points`.`longi`, featured, kmlno, image_url, category.title, category_id, point_id, lat, longi, reviews.star_points, reviews.review_id, count(reviews.point_id) as totals FROM (SELECT *, ( 3959 * acos( cos( radians('37.7717185') ) * cos( radians( lat ) ) * cos( radians( longi ) - radians('-122.4438929') ) + sin( radians('37.7717185') ) * sin( radians( lat ) ) ) ) AS distance FROM points HAVING distance < '25') as distResults LEFT JOIN category USING ( category_id ) LEFT JOIN reviews USING ( point_id ) WHERE (point_title LIKE '%Playgrounds%' OR category.title LIKE '%Playgrounds%') GROUP BY point_id ORDER BY totals DESC, distance LIMIT 0 , 10

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• Pre-packaged Rails applications

  - by Craig

  Seems like most Rails applications have similar 'base' functionality. As such, it seems that there would be value in having pre-build Rails applications at various functionality points such as: basic User model with authentication using Authlogic #1 + openid integration #2 + authorization using declarative_authorization #3 + Administration module #4 + a Profile model Themes (useful stylesheets and such) Friendship model Geocoding ... In addition to the basic MVC stuff, these applications would include: testing harnesses seed data git support One could choose start from any of these functionality points. Other than the sample application that are available with the various gems/plugins, are there projects such as these? If not, I would certainly be willing to contribute what I have.

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• How to calculate a point with an given center, angle and radius?

  - by mystify

  In this SO question, someone asked for calculating an angle from three points. I need to do the opposite thing. I want to draw a clock, and I have tiny tick images. An art dude made 60 of them, each with an individual and accurate shadow. So there are 60 distinct images at 10x10 points in size, already correctly rotated in the center of that square. So every 6 degrees one tick image has to be placed. I would just need to calculate the x/y coordinate based on a center point, an radius and an angle. So I have: an center point an radius an angle Is there an easy way to calculate the x/y coordinate with this? Maybe cocoa-touch already has a useful function or method for this?

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