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• Polygon area calculation using Latitude and Longitude generated from Cartesian space and a world fil

  - by Heath

  Given a series of GPS coordinate pairs, I need to calculate the area of a polygon (n-gon). This is relatively small (not larger than 50,000 sqft). The geocodes are created by applying an affine transform with data from a world file. I have tried to use a two step approach by doing converting the geocodes to cartesian coordinates: double xPos = (lon-lonAnchor)*( Math.toRadians( 6378137 ) )*Math.cos( latAnchor ); double yPos = (lat-latAnchor)*( Math.toRadians( 6378137 ) ); then I use a cross product calculation to determine the area. The issue is that the results are a bit off in accuracy (around 1%). Is there anything I can look into to improve this? Thanks.

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• Mobile Safari Geolocation API Issues

  - by sph

  Hi, since Mobile Safari's Geolocation API should be an implementation of the W3C Geolocation API I found some bugs. I was wondering if anybody noticed the same. As specified in the W3C Geolocation API the PositionCallback returns a Position object, which contains a Coordinates object. In this object all attributes are of type double. Using navigator.geolocation.getCurrentPosition and checking the Position object in the successCallback the accuracy attribute is always an object, but should be a double. The heading attribute is always -1 when testing in the iPhone simulator, but should be null or between 0 and 360. 2. Setting the options parameter for navigator.geolocation.watchPosition or navigator.geolocation.getCurrentPosition as specified in the W3C Geolocation API has no effect. No matter what is set as the timeout value, the win callback is called every 10 seconds. For example setting the timeout=1000 should immediately call either the successCallback or errorCallback. Thanks

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• Memory footprint of a parsed XML file in Classic ASP?

  - by Pete Duncanson

  Anyone know of a way to find out the amount of memory/size of a XMLDocument once it has parsed a XML file? I've been doing "beer mat" calculations so far but have been asked to come up with some more legit numbers through monitoring some how. I need to create about 1500 XML files (via FreeThreadedXMl-DOM object), which verge between 3-9K in size and store them in Application vars but our SysAdmin is worried about us gobbling up too much memory. Other than the crude method of booting up a fresh IIS instance and then loading everything in and monitoring before and after memory usage in Task Manager I can't think of a way of doing it with a bit more accuracy.

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• how to read specific number of floats from file in python?

  - by sahel

  I am reading a text file from the web. The file starts with some header lines containing the number of data points, followed the actual vertices (3 coordinates each). The file looks like: # comment HEADER TEXT POINTS 6 float 1.1 2.2 3.3 4.4 5.5 6.6 7.7 8.8 9.9 1.1 2.2 3.3 4.4 5.5 6.6 7.7 8.8 9.9 POLYGONS the line starting with the word POINTS contains the number of vertices (in this case we have 3 vertices per line, but that could change) This is how I am reading it right now: ur=urlopen("http://.../file.dat") j=0 contents = [] while 1: line = ur.readline() if not line: break else: line=line.lower() if 'points' in line : myline=line.strip() word=myline.split() node_number=int(word[1]) node_type=word[2] while 'polygons' not in line : line = ur.readline() line=line.lower() myline=line.split() i=0 while(i<len(myline)): contents[j]=float(myline[i]) i=i+1 j=j+1 How can I read a specified number of floats instead of reading line by line as strings and converting to floating numbers? Instead of ur.readline() I want to read the specified number of elements in the file Any suggestion is welcome..

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• Can I use Win32 FreeType without the .dll file?

  - by Khatharr

  Hello. I'm teaching myself OpenGL and I'm implementing ttf text rendering using FreeType 2. I downloaded the library from http://gnuwin32.sourceforge.net/packages/freetype.htm and after a couple of minor issues I got it running properly. The thing that's bothering me is that I have to place a copy of freetype6.dll in the directory with my executable in order for the thing to run. I generally try to avoid a bunch of unnecessary dll files floating around. I'm sort of new to windows programming, but from what I understand most libraries can be built to run fully from a lib rather than requiring a dll at runtime. Looking through the documentation from FT is making my brain melt, so I thought I would ask here to see if there were any devs that have worked with FT before and if so, do they know how to build the library such that no dll is required at runtime. Thank you in advance for any advice or support.

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• AVR Analog Comparator + Internal Pullup?

  - by vicatcu

  I have what I hope is a simple question pertaining to the Atmel AVR microcontrollers. So I want to use the ATTiny85's Analog Comparator to determine if a signal is above or below a threshold. This signal is normally "floating" and grounded when "active" (i.e. it's an active low - open collector signal). If I enable the pullup on the input pin (which is also the comparator input) by doing: DDRB = 0x00; // DDRB.1 = 0 = input PORTB = 0xFF; // PORTB.1 = 1 = internal pullup enabled If i use the analog comparator and select PORTB.1 as AIN1 will the internal pullup be applied to my input signal? I'm hoping someone has personal experience to verify this behavior. Hope this question isn't too 'hardware-oriented' for stack-overflow. Thanks!

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• How do you detect a website visitor's country (Specifically, US or not)?

  - by BigDave

  I need to show different links for US and non-US visitors to my site. This is for convenience only, so I am not looking for a super-high degree of accuracy, and security or spoofing are not a concern. I know there are geotargeting services and lists, but this seems like overkill since I only need to determine (roughly) if the person is in the US or not. I was thinking about using JavaScript to get the user's timezone, but this appears to only give the offset, so users in Canada, Mexico, and South America would have the same value as people in the US. Are there any other bits of information available either in JavaScript, or PHP, short of grabbing the IP address and doing a lookup, to determine this?

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• Where are TFS Alerts stored in the TFS Databases? Receiving duplicate alerts after upgrade 2008 to

  - by MJ Hufford

  I recently performed a migration-upgrade from TFS 2008 to TFS 2010. Almost everything is working properly now. However, our team is getting duplicate emails now. I'm guessing this is because I used the TFS 2008 power tools to setup alerts. After the upgrade, I installed the TFS 2010 power tools and noticed that there were not alerts configured. I setup new alerts and now we get duplicates. Is it possible the old alerts configuration is floating around in the db somewhere?

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• Merge overlapping triangles into a polygon

  - by nornagon

  I've got a bunch of overlapping triangles from a 3D model projected into a 2D plane. I need to merge each island of touching triangles into a closed, non-convex polygon. The resultant polygons shouldn't have any holes in them (since the source data doesn't). Many of the source triangles share (floating point identical) edges with other triangles in the source data. What's the easiest way to do this? Performance isn't particularly important, since this will be done at design time.

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• How to know coordinates in a real image from a scaled image.

  - by ocell

  Hi folks, First of all thanks for your time reading my question :-) I have an original image (w': 2124, h': 3204) and the same image scaled (w: 512, h: 768). The ratio for width is 4.14 (rw) and the ratio for height is 4.17 (rh). I'm trying to know the coordinates (x', y') in the original image when I receive the coordinates in the scaled image (x, y). I'm using the formula: x' = x * rw and y' = y * rh. But when I'm painting a line, or a rectangle always appears a shift that is incremented when x or y is higher. Please anybody knows how to transform coordinates without loosing of accuracy. Thanks in advance! Oscar.

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• .net converting bytearray to double[]

  - by AJ

  Hello, I am working with a database from a legacy app which stores 24 floating point values (doubles) as a byte array of length 192, so 8 bytes per value. This byte array is stored in a column of type image in a SQL Server 2005 database. In my .net app I need to read this byte array and convert it to a array of type Double[24]. I can access the field easy enough reader.GetBytes(...) but how to convert the returned ByteArray to Double[24] Any ideas? Thanks, AJ

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• Good .NET library for fast streaming / batching trigonometry (Atan)?

  - by Sean

  I need to call Atan on millions of values per second. Is there a good library to perform this operation in batch very fast. For example, a library that streams the low level logic using something like SSE? I know that there is support for this in OpenCL, but I would prefer to do this operation on the CPU. The target machine might not support OpenCL. I also looked into using OpenCV, but it's accuracy for Atan angles is only ~0.3 degrees. I need accurate results.

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• pgf/tikz: String Symbols as Input Coordinates

  - by red_lynx

  Hi all, I'm new to pgf so i was trying out some examples from the pgfplot manual. One example is especially relevant for my current task but, alas, it would not compile. Here is the code: \documentclass[11pt]{article} \usepackage{tikz} \usepackage{pgfplots} \begin{document} \begin{tikzpicture} \begin{axis}[symbolic x coords={a,b,c,d,e,f,g,h,i}] \addplot+[smooth] coordinates { (a,42) (b,50) (c,80) (f,60) (g,62) (i,90)}; \end{axis} \end{tikzpicture} \end{document} the compiler quits with the following error: ! Package PGF Math Error: Could not parse input 'a' as a floating point number, sorry. The unreadable part was near 'a'.. I have no clue how to correct this behavior. Other plots (smooth, scatter, bar), which contain only numerical data compile fine. Could anybody give me a hint? Cheers K.

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• So does Apple recommend to not use predicates and sort descriptors in an NSFetchRequest?

  - by dontWatchMyProfile

  From the docs: To summarize, though, if you execute a fetch directly, you should typically not add Objective-C-based predicates or sort descriptors to the fetch request. Instead you should apply these to the results of the fetch. If you use an array controller, you may need to subclass NSArrayController so you can have it not pass the sort descriptors to the persistent store and instead do the sorting after your data has been fetched. I don't get it. What's wrong with using them on fetch requests? Isn't it stupid to get back a whole big bunch of managed objects just to pick out a 1% of them in memory, leaving 99% garbage floating around? Isn't it much better to only fetch from the persistent store what you really need, in the order you need it? Probably I did get that wrong...

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• C++ double division by 0.0 versus DBL_MIN

  - by wonsungi

  When finding the inverse square root of a double, is it better to clamp invalid non-positive inputs at 0.0 or MIN_DBL? (In my example below double b may end up being negative due to floating point rounding errors and because the laws of physics are slightly slightly fudged in the game.) Both division by 0.0 and MIN_DBL produce the same outcome in the game because 1/0.0 and 1/DBL_MIN are effectively infinity. My intuition says MIN_DBL is the better choice, but would there be any case for using 0.0? Like perhaps sqrt(0.0), 1/0.0 and multiplication by 1.#INF000000000000 execute faster because they are special cases. double b = 1 - v.length_squared()/(c*c); #ifdef CLAMP_BY_0 if (b < 0.0) b = 0.0; #endif #ifdef CLAMP_BY_DBL_MIN if (b <= 0.0) b = DBL_MIN; #endif double lorentz_factor = 1/sqrt(b); double division in MSVC: 1/0.0 = 1.#INF000000000000 1/DBL_MIN = 4.4942328371557898e+307

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• Perl Math::Business::EMA help

  - by Dustin

  Script pulls data from mysql: $DBI::result = $db->prepare(qq{ SELECT close FROM $table WHERE day <= '$DATE' ORDER BY day DESC LIMIT $EMA }); $DBI::result->execute(); while($row = $DBI::result->fetchrow) { print "$row\n"; }; with the following example results: 1.560 1.560 1.550... But I need to work out the EMA using Math::Business::EMA; and I'm not sure how to calculate this while maintaining the accuracy. EMA is weighted and My lack of Perl knowledge is not helping.

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• Handling Datetime with decimal '2010-02-14 20:18:58.313000000'

  - by AaronLS

  In SQL Server I have some textual data in varchar fields I am trying to convert to datetime's. The funny thing is this data at some point was in a datetime field, exported to flat file, and now I am reimporting it. The problem is it is in this format 2010-02-14 20:18:58.313000000 and the conversion to datetime fails. I have no idea how it ended up like this when it was originally extracted from a datetime column. Basically a table was exported to a flat file by someone else. The original table was lost. I am reimporting back from the flatfile. I could just drop the decimal but this would be like throwing out some of the data. I'd like to maintain as much precision as possible. How can I import this data from the varchar column back into a datetime column and preserve as much accuracy as possible?

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• margin between content and div overflow scrollbar

  - by ben

  I am using the following bits of code to keep my menu items fixed while allowing for the scrolling of content because it seems to be the most stable method across all browsers. body { overflow: hidden; } div.content { height: 100%; overflow: auto; } My problem is simple, and yet I can not seem to figure it out, the content inside the tag butts up against the scrollbar for the div area and it makes reading much more difficult. How can I get a margin between them (apart from floating a transparent image to the right to create space, there HAS to be a better way)?

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• How precise is the internal clock of a modern PC?

  - by mafutrct

  I know that 10 years ago, typical clock precision equaled a system-tick, which was in the range of 10-30ms. Over the past years, precision was increased in multiple steps. Nowadays, there are ways to measure time intervals in actual nanoseconds. However, usual frameworks still return time with a precision of only around 15ms. My question is, which steps did increase the precision, how is it possible to measure in nanoseconds, and why are we still often getting less-than-microsecond precision (for instance in .NET). (Disclaimer: It strikes me as odd that this was not asked before, so I guess I missed this question when I searched. Please close and point me to the question in that case, thanks. I believe this belongs on SO and not on any other SOFU site. I understand the difference between precision and accuracy.)

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• Geocode multiple addresses

  - by ace2600

  I need to geocode around 200 addresses per request and do around 3,000 request per day. I will be doing this server side using PHP. I have looked at http://stackoverflow.com/questions/98449/how-to-convert-an-address-to-a-latlon, but could not find a way for either Google Maps HTTP Request API or the Yahoo Geocoding REST API (cannot use JavaScript as this is server side) to send multiple addresses. I will be primarily using this to sort addresses based on the coordinates and if the API supports, fill in any missing data for each address. The addresses will be in the United States only. The addresses to geocode will be from user input, so be free form, like "street address, postal code", or "city, state", etc. Accuracy is not too important for the coordinates, say within five hundred feet or so. Is there a free API to handle this? Is there a way to get Yahoo or Google to do multiple locations in a request?

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• Redundancy algorithm for reading noisy bitstream

  - by Tedd Hansen

  I'm reading a lossy bit stream and I need a way to recover as much usable data as possible. There can be 1's in place of 0's and 0's in palce of 1's, but accuracy is probably over 80%. A bonus would be if the algorithm could compensate for missing/too many bits as well. The source I'm reading from is analogue with noise (microphone via FFT), and the read timing could vary depending on computer speed. I remember reading about algorithms used in CD-ROM's doing this in 3? layers, so I'm guessing using several layers is a good option. I don't remember the details though, so if anyone can share some ideas that would be great! :) Edit: Added sample data Best case data: in: 0000010101000010110100101101100111000000100100101101100111000000100100001100000010000101110101001101100111000101110000001001111011001100110000001001100111011110110101011100111011000100110000001000010111 out: 0010101000010110100101101100111000000100100101101100111000000100100001100000010000101110101001101100111000101110000001001111011001100110000001001100111011110110101011100111011000100110000001000010111011 Bade case (timing is off, samples are missing): out: 00101010000101101001011011001110000001001001011011001110000001001000011000000100001011101010011011001 in: 00111101001011111110010010111111011110000010010000111000011101001101111110000110111011110111111111101 Edit2: I am able to controll the data being sent. Currently attempting to implement simple XOR checking (though it won't be enough).

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• Site hosted with Blogger has some display problems in IE

  - by dafactopedia

  Hello guys..My site url is : Da Factopedia It opens up perfectly in all browsers Firefox, Opera, Safari, Chrome. Even in IE 8 the Home page is perfectly displayed . But if you click on any post page like this one : http://www.dafactopedia.com/2010/03/7-surprising-facts-about-sleep.html the right sidebar starts acting up. It starts floating within the main post area and I have no clue why this happens. Here is the template xml code in a txt file : http://www.opendrive.com/files/6244724_nPpSE_bf53/template.txt in xml format : http://www.opendrive.com/files/6244723_40eAI_3e95/template-6257961483006208180(4).xml

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• Static struct in C++

  - by pingvinus

  Hi, I want to define an structure, where some math constants would be stored. Here what I've got now: struct consts { //salt density kg/m3 static const double gamma; }; const double consts::gamma = 2350; It works fine, but there would be more than 10 floating point constants, so I doesn't want to wrote 'static const' before each of them. And define something like that: static const struct consts { //salt density kg/m3 double gamma; }; const double consts::gamma = 2350; It look fine, but I got these errors: 1. member function redeclaration not allowed 2. a nonstatic data member may not be defined outside its class I wondering if there any C++ way to do it?

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• How to improve performance

  - by Ram

  Hi, In one of mine applications I am dealing with graphics objects. I am using open source GPC library to clip/merge two shapes. To improve accuracy I am sampling (adding multiple points between two edges) existing shapes. But before displaying back the merged shape I need to remove all the points between two edges. But I am not able to find an efficient algorithm that will remove all points between two edges which has same slope with minimum CPU utilization. Currently all points are of type PointF Any pointer on this will be a great help.

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• Most efficient algorithm for mesh-level, optimal occlusion culling?

  - by Fredriku73

  I am new to culling. On a first glance, it seems that most occlusion culling algorithms are object-level, not examining single meshes, which would be practical for game rendering. What I am looking for is an algorithm that culls all meshes within a single object that are occluded for a given viewpoint, with high accuracy. It needs to be at least O(n log n), a naive mesh-by-mesh comparison (O(n^2)) is too slow. I notice that the Blender GUI identifies the occluded meshes for you in real-time, even if you work with large objects of 10,000+ meshes. What algorithm is used there, pray tell?

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