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Search found 439 results on 18 pages for 'accuracy'.

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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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• 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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• 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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• 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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• 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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• 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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• Fade a color to white (increasing brightness)

  - by Jon B

  I want to make a text box in .NET "glow" yellow, and then "fade" to white (basically, by incrementally increasing the brightness). I think Stackoverflow does this after you've posted an answer. I know that increasing brightness is not all that simple (it's not just uniformly increasing/decreasing RGB), but I'm not sure how to do this. Perfect color accuracy is not important for this. I am using C#, although VB examples would be just fine, too. Edit: This is for Winforms.

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• What is the best Java numerical method package?

  - by Bob Cross

  I am looking for a Java-based numerical method package that provides functionality including: Solving systems of equations using different numerical analysis algorithms. Matrix methods (e.g., inversion). Spline approximations. Probability distributions and statistical methods. In this case, "best" is defined as a package with a mature and usable API, solid performance and numerical accuracy. Edit: derick van brought up a good point in that cost is a factor. I am heavily biased in favor of free packages but others may have a different emphasis.

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• Division to the nearest 1 decimal place without floating point math?

  - by John Sheares

  I am having some speed issues with my C# program and identified that this percentage calculation is causing a slow down. The calculation is simply n/d * 100. Both the numerator and denominator can be any integer number. The numerator can never be greater than the denominator and is never negative. Therefore, the result is always from 0-100. Right now, this is done by simply using floating point math and is somewhat slow, since it's being calculated tens of millions of times. I really don't need anything more accurate than to the nearest 0.1 percent. And, I just use this calculated value to see if it's bigger than a fixed constant value. I am thinking that everything should be kept as an integer, so the range with 0.1 accuracy would be 0-1000. Is there some way to calculate this percentage without floating point math?

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• Bash: Check if file was modified since used in script

  - by Thomas Münz

  I need to check in a script if a file was modified since I read it (another application can modify it in between). According to bash manual there is a "-N" test which should report if a file was modified since last read. I tried it in a small script but it seems like it doesn't work. #!/bin/bash file="test.txt" echo "test" > $file cat $file; if [ -N $file ]; then echo "modified since read"; else echo "not modified since read"; fi I also tried an alternative way by touching another file and using if [ "file1" -nt "file2 ]; but this works only on a seconds accuracy which may under rare conditions not be sufficient. Is there any other bash-inbuilt solution for this problem or I do really need to use diff or md5sum?

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• Implementing tracing gestures on iPhone

  - by bmoeskau

  I'd like to create an iPhone app that supports tracing of arbitrary shapes using your finger (with accuracy detection). I have seen references to an Apple sample app called "GestureMatch" that supposedly implemented exactly that, but it was removed from the SDK at some point and I cannot find the source anywhere via Google. Does anyone know of a current official sample that demonstrates tracing like this? Or any solid suggestions on other resources to look at? I've done some iPhone programming, but not really anything with the graphics API's or custom handling of touch gestures, so I'm not sure where to start.

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• Programming with midi, and tuning notes to specific frequencies

  - by froggie0106

  I am working on a project in which I need to be able to generate midi notes of varying frequencies with as much accuracy as possible. I originally tried to write my program in Java, but it turns out that the sound.midi package does not support changing the tunings of notes unless the frequencies are Equal Tempered frequencies (or at least it didn't in 1.4, and I haven't been able to find evidence that this has been fixed in recent versions). I have been trying to find a more appropriate language/library to accomplish this task, but since this is my first time programming with MIDI and my need for specific tuning functionality is essential, I have been having considerable trouble finding exactly what I need. I am looking for advice from people who have experience writing MIDI programs as to what languages are useful, especially for tuning notes to specific frequencies. Any links to websites with API docs and example code would also be extremely helpful.

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• code throws std::bad_alloc, not enough memory or can it be a bug?

  - by Andreas

  I am parsing using a pretty large grammar (1.1 GB, it's data-oriented parsing). The parser I use (bitpar) is said to be optimized for highly ambiguous grammars. I'm getting this error: 1terminate called after throwing an instance of 'std::bad_alloc' what(): St9bad_alloc dotest.sh: line 11: 16686 Aborted bitpar -p -b 1 -s top -u unknownwordsm -w pos.dfsa /tmp/gsyntax.pcfg /tmp/gsyntax.lex arbobanko.test arbobanko.results Is there hope? Does it mean that it has ran out of memory? It uses about 15 GB before it crashes. The machine I'm using has 32 GB of RAM, plus swap as well. It crashes before outputting a single parse tree. The parser is an efficient CYK chart parser using bit vector representations; I presume it is already near the limit of memory efficiency. If it really requires too much memory I could sample from the grammar rules, but this will decrease parse accuracy of course.

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• Java library for converting Word documents to PDFs or images

  - by mieze

  Hey there What I need to do is convert Microsoft Word .doc files to PDFs or images. This has to occur in Java. I have done a fair bit of investigation already. I've tried Davisor Publishor but it doesn't give me the accuracy that I need - for instance text overlapping in the output document. Adobe has something called LiveCycle. Anyone tried this? It looks quite massive and a bit of overkill (its an "integrated server solution"). Sounds expensive. Saying that, it doesn't have to be free, or cheap. Even if you just know some names, please shout them my way. Many thanks in advance. Doug

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• How can I test if a point lies within a 3d shape with its surface defined by a point cloud?

  - by Ben

  Hi I have a collection of points which describe the surface of a shape that should be roughly spherical, and I need a method with which to determine if any other given point lies within this shape. I've previously been approximating the shape as an exact sphere, but this has proven too inaccurate and I need a more accurate method. Simplicity and speed is favourable over complete accuracy, a good approximation will suffice. I've come across techniques for converting a point cloud to a 3d mesh, but most things I have found have been very complicated, and I am looking for something as simple as possible. Any ideas? Many thanks, Ben.

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• For what purpose does java have a float primitive type?

  - by Roman

  I heard plenty times different claims about float type in java. The most popular issues typicaly regard to converting float value to double and vice versa. I read (rather long time ago and not sure that it's actual now with new JVM) that float gives much worse performance then double. And it's also not recommended to use float in scientific applications which should have certain accuracy. I also remember that when I worked with AWT and Swing I had some problems with using float or double (like using Point2D.Float or Point2D.Double). So, I see only 2 advantages of float over double: it needs only 4 bytes while double needs 8 bytes JMM garantees that assignment operation is atomic with float variables while it's not atomic with double's. Are there any other cases where float is better then double? Do you use float's in your applications? It seems to me that the only valuable reason java has float is backward compatibility.

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• Rejigging a floating point equation ...

  - by Jamie

  I'd like to know if there is a way to improve the accuracy of calculating a slope. (This came up a few months back here). It seems by changing: float get_slope(float dXa, float dXb, float dYa, float dYb) { return (dXa - dXb)/(dYa - dYb); } to float get_slope(float dXa, float dXb, float dYa, float dYb) { return dXa/(dYa - dYb) - dXb/(dYa - dYb); } might be an improvement. Suggestions? Edit: It's precision I'm after, not efficiency.

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• Looking for Info on a Javascript Testing framework

  - by DaveDev

  Hi Can somebody fill me in on JavaScript Testing Frameworks? I'm working on a project now and as the JS (Mostly jQuery) libraries grow, it's getting more and more difficult to introduce change or refactor, because I have no way of guaranteeing the accuracy of the code without manually testing everything. I don't really know anything about JavaScript Testing Frameworks, or how they integrate/operate in a .Net project, so I thought I'd ask here. What would a good testing framework be for .Net? What does a JavaScript test look like? (e.g. with NUnit, I have [TestFixture] classes & [Test] methods in a ProjectTests assembly) How do I run a javascript test? What are the conceptual differences between testing JS & testing C#? Is there anything else that would be worth knowing? Thanks Dave

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• Efficiently remove points with same slope

  - 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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• Real-Time Data Streaming to Multiple Clients

  - by AriX

  Hi all, I would like to write an application which will stream data at 2400 baud over the internet from a server to multiple clients. The data will be the same for each client, and it would probably be fine to send it as a UDP stream, since exact data accuracy is not a 100% necessity, as there are checksums built-in to the data format and the data will be sent repeatedly on a loop. What is the best way to do this? I would want to write the server in C, but I don't know how to best multicast this data to the different clients that would be receiving it all over the country. I'm sure this seems like a pretty draconian way to go about my project, as opposed to just using some sort of fetch command, but I'd prefer to do it this way if possible.

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• Floating point precision nuances.

  - by user247077

  Hi, I found this code in NVIDIA's cuda SDK samples. void computeGold( float* reference, float* idata, const unsigned int len) { reference[0] = 0; double total_sum = 0; unsigned int i; for( i = 1; i < len; ++i) { total_sum += idata[i-1]; reference[i] = idata[i-1] + reference[i-1]; } // Here it should be okay to use != because we have integer values // in a range where float can be exactly represented if (total_sum != reference[i-1]) printf("Warning: exceeding single-precision accuracy. Scan will be inaccurate.\n"); } (C) Nvidia Corp Can somebody please tell me a case where the warning would be printed, and most importantly, why. Thank you very much.

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• getting the value of a filter at an arbitrary time

  - by Andiih

  Context: I'm trying to improve the values returned by the iPhone CLLocationManager, although this is a more generally applicable problem. The key is that CLLocationManger returns data on current velocity as and when it feels like it, rather than at a fixed sample rate. I'd like to use a feedback equation to improve accuracy v=(k*v)+(1-k)*currentVelocity where currentVelocity is the speed returned by didUpdateToLocation:fromLocation: and v is the output velocity (and also used for the feedback element). Because of the "as and when" nature of didUpdateToLocation:fromLocation: I could calculate the time interval since it was last called, and do something like for (i=0;i<timeintervalsincelastcalled;i++) v=(k*v)+(1-k)*currentVelocity which would work, but is wasteful of cycles. Especially as I probably want timeintervalsincelastcalled to be measured as 10ths of a second. Is there a way to solve this without the loop ? i.e. rework (integrate?) the formula so I put an interval into the equation and get the same answer as I would have by iteration ?

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