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datahead8888

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  1. I have a series of vectors, each of which is assigned to one of 6 cube map walls and an x/y value on those walls, depending on each vector's direction.   The full set of possible vector directions corresponds to a sphere, while the walls of the cube map are each 2D.   If I want to search for vectors pointing in directions along a circular region along the surface of this sphere, this circle on the surface of the sphere would have to be projected or otherwise transformed onto the surface of the cube map, in order to account for the distortion.  I assume it would be a derived form of a point in circle test ultimately.   Likewise, if I query a rectangular region on the surface of the sphere, this too much be projected or otherwise transformed to account for distortion.   What kind of techniques or relationships might be helpful in transforming this test?  I can't seem to find any lead on it.
  2. Suppose you have a parametric equation for a surface, for example:     x = 3*cos(s)+cos(t)*cos(s) y = 3*sin(s)+cos(t)*sin(s) z = sin(t)   The partial derivative of this wrt s is: dsx = -3*sin(s)-cos(t)*sin(s) dsy = 3*cos(s)+cos(t)*cos(s) dsz = 0   The partial derivative of this wrt t is: dtx = -sin(t)*cos(s) dty = -sin(t)*sin(s) dtz = cos(t)   Which of these is the tangent in the s direction, and which of these is the tangent in the t direction?  I would have thought the tangent in the s direction is the derivative wrt s above and that the tangent in the t direction is the derivative wrt t, but I seem to remember hearing the opposite.
  3. Does anyone know of an open source equivalent to Autodesk Mudbox that allows virtual sculpting of an object?   Simpler is better.  I was interested in using the user interface in such a tool for a programming project...
  4. Okay, if you find out let me know.  I gave up on using the devil debugger for this set of changes but would love to use it for the next set of changes.
  5. I downloaded GLSL Devil in order to try and debug GLSL shader code, here: http://wwwvis.informatik.uni-stuttgart.de/glsldevil/index.html#usage   I want to use it with Visual C++ (2010), but am not sure how to hook up GLSL Devil to Visual C++.   I tried telling GLSL Devil to load both my .vert and .frag files for GLSL, but it does not seem to do anything with them.   I used the shader set up code at - http://www.cse.ohio-state.edu/~hwshen/5542/Site/Slides_files/shaderSetup.C Is this code not saving a binary file to disk that I need to connect GLSL Devil to?   Both my .vert and .frag files work at the moment - they are successfully transforming vertices and applying colors as needed.  I just want to use GLSL Devil to help debug some additional changes I need to make.
  6. This probably would work if I just needed the derivative of something to be applied during a simple physics implementation, but I need to arbitrarily find the Jacobian matrix so that it can be fed into a conjugate gradient implementation that solves a system of equations.  What I'm doing is a bit theoretical, but it would still need be able to be implemented.   Writing a program like this to find it is an interesting idea - I wonder if I could construct some sort of list or other data structure that keeps track of my terms as they're found?
  7. To be clear - the Jacobian I find will be programmed into C++. I'm not creating a system to find Jacobians arbitrarily.
  8. I'm doing it by hand.  It will then be programmed into C++.
  9. I was working on a physics animation, and I need to compute the Jacobian in order to solve a partial differential equation.   Suppose we have a function consisting of a series of matrices multiplied by a vector: f(X) = A * B * b --where X is a vector containing elements that are contained within A, b, and/or b, --A is a matrix, B is a matrix, and b is a vector Each Matrix and the vector is expressed as more terms, ie... X = (x1, x2, x3) A = [ x1 + y1        y4       y7 ] [      y2   x2 + y5       y8 ] ]      y3        y6  x3 + y9 ] B = [      y1   x2 + y4  x3 + y7 ] [x1 +  y2        y5       y8 ] ]      y3        y6       y9 ] b = [y1 y2 y3]'  (' means transposed) Now we want to find the Jacobian of f - ie the partial derivative of f wrt X. One way to do this is to multiply the two matrices and then multiply that by the vector, creating one 3x1 vector in which each element is an algebraic expression resulting from matrix multiplication.  The partial derivative could then be computed per element to form a 3x3 Jacobian.  This would be feasible in the above example, but the one I'm working is a lot more complicated (and so I would also have to look for patterns in order to simplify it afterwards). I was wanting to try to use the chain rule and/or the product rule for partial derivatives if possible.  However, with the product rule you end up with A' * B * b + A * B' * b + A * B * b', where each derivative is wrt to the vector X.  I understand that the derivative of a matrix wrt a vector is actually a 3rd order tensor, which is not easy to deal with.  If this is not correct, the other terms still have to evaluate to matrices in order for matrix addition to be valid.  If I use the chain rule instead, I still end up with the derivative of a matrix wrt a vector. Is there an easier way to break down a matrix calculus problem like this?  I've scoured the web and cannot seem to find a good direction.  
  10. Suppose I have a 2D triangle.  It would have 3 vertices with 2D coordinates - (ua, va), (ub, vb), (uc, vc). How could these be represented with parametric coordinates? For example, if it was an equilateral triangle, what would the parametric coordinates be?   I've looked around for references but never find anything that can easily be applied to triangles.  Most people post guides on parametric equations and polar coordinates, which is a different topic.  
  11. I've been working on an OpenGL program and wanted to create a "video generation mode" where it outputs to a series of numbered targa files that can later be collated with a video editing tool.  I'm using glut with OpenGL (without shaders) and Visual C++ express on Windows.   What I've found is that it works fine when the window is open -- each output targa image is correct.   The moment I close the window, I found that the rendering code keeps running -- if I have cout's they keep printing to the console.  If does not render correctly to the targa images at that point - every other frame it is upside down and swaps red and blue. If I could detect window close events, I could terminate the application on a window close so that it stops outputting targa images, but this version of glut does not have that callback and freeglut is not an option.   The relevant code is below...           //The following section is after the openGL rendering code                 glReadBuffer(GL_BACK); //Tried with and without this line         glFlush();  //Tried with and without this line                 //This does the buffer read         glReadPixels(0, 0, windowWidth, windowHeight, GL_RGBA, GL_UNSIGNED_BYTE, screenBuffer);           //Vertically flip the image in memory - it flips two rows from the screen in memory at a time         //The images will be upside down without this         for (int i = 0; i < windowHeight / 2; i++)         {             if (i != windowHeight - i)             {                 memcpy(temp,(uint8_t *)&screenBuffer[i * windowWidth * 4], windowWidth * 4 * sizeof(uint8_t));                 memcpy((uint8_t *)&screenBuffer[i * windowWidth * 4], (uint8_t *)&screenBuffer[(windowHeight - i) * windowWidth * 4], windowWidth * 4 * sizeof(uint8_t));                 memcpy((uint8_t *)&screenBuffer[(windowHeight - i) * windowWidth * 4], temp, windowWidth * 4 * sizeof(uint8_t));                         }         }           //I used the C targa library at -- http://dmr.ath.cx/gfx/targa/         sprintf(imageFileName, "videoFile%d.tga", frameNumber);         tga_result result = tga_write_rgb(imageFileName, screenBuffer, windowWidth, windowHeight, 32);           frameNumber++;
  12. I was trying to implement Shape Context in order to identify a single textual character. I was trying to achieve rotation invariance. The general approach for shape context is to compute distances and angles between each set of interest points in a given image. You then bin into a histogram based on whether these calculated values fall into certain ranges. You do this for both a standard and a test image. To match two different images, from this you use a chi-square function to estimate a "cost" between each possible pair of points in the two different histograms. Finally, you use an optimization technique such as the hungarian algorithm to find optimal assignments of points and then sum up the total cost, which will be lower for good matches. I've checked several websites and papers, and they say that to make the above approach rotation invariant, you need to calculate each angle between each pair of points using the tangent vector as the x-axis. (ie http://www.cs.berkeley.edu/~malik/papers/BMP-shape.pdf page 513) What exactly does this mean? No one seems to explain it clearly. Also, from which of each pair of points would you get the tangent vector - would you average the two? A couple other people suggested I could use gradients (which are easy to find in toolsets such as Matlab) and use this as a substitute for the tangent points, though it does not seem to compute reasonable cost scores with this. Is it feasible to do this with gradients?
  13. I meant programming the 3D movement and rendering of objects, often done in movies but possibly applied to video games (interactive play or in cut scenes). I said computer science because I meant the more technical side of it (programming, math, etc). There is also an "art side" of it, but I wasn't interested in this focus.
  14. I apologize for asking too broad of a question. What I meant to ask is - Do people think Ohio State University or the University of Pennsylvania has a better repuation for animation for computer science now? The University of Pennsylvania seems to have more professors that study topics in animation now, but Ohio State University seems to have had more of a historical influence in years gone by and has more professors in graphics in general now.
  15. I've been applying to several schools for graduate work in computer science. My interests are graphics, physics simulations, interactive simulations, and artificial intelligence. I currently work in Information Technology and could use a lot more training in my computer science areas of interest. These are two of the best looking offers I received. [color=#008000]Does anyone know if the University of Pennsylvania (UPenn) or Ohio State University is better if I decided I wanted to focus on the animation side of graphics programming (possibly interactive)?[/color] It sounds like Ohio State has historically had a strong suit here, but I was concerned some of the animation professors may have left in recent years. Ohio State does have a broader study in graphics, however. [b]UPenn ([/b]http://cg.cis.upenn.edu)[b]:[/b] --Ivy League institution --#17 in Computer Science --3 professors that heavily focus on animation (or games). Also has a more expansive game development program. --4 total graphics professors. It sounds like their graphics and game development programs are very well respected. --They may have stronger AI - I saw 3 computer vision professors --Admission to masters program. This Masters of Science of Engineering is NOT easily transferred to a PhD program at UPenn, but it is possible --Financial support can be applied for but is limited for masters students. Tuition cost is $55,000 for degree (probably 2 - 2.5 years). --Industry connections look very good - Pixar, Dreamworks, Disney, Electronic Arts, Microsoft, Sony, Activision, Blue Sky Entertainment [b]Ohio State University[/b] (http://www.cse.ohio-state.edu/research/graphics/ and http://www.cse.ohio-state.edu/~parent/) --Was noted for being a public institution with a rigor comparable to an Ivy League institution - a "public Ivy" --#28 in Computer Science --Only 1 professor that directly focuses research on animation. They do have more breadth in areas of graphics, however (animation, science, medical, computational geometry). --7 total graphics professors. From what I'm hearing their graphics program is probably premiere. --They don't have as dedicated of a "game development" program but they do have classes in it, and the courses teach the main topics one would need to know. --The AI does look innovative - the computer vision project identifies suspicious behavior of thieves in parking lots. I know they also do sound analysis. --Admission to PhD program. It is possible to downgrade to a masters if necessary by petitioning a committee. --Full tuition waiver and stipend (with PhD program and Graduate Teaching Assistantship position). Without a waiver I think out of state tuition is $26,000 / year, but it may be cheaper. --I have seen very good industry connections - Graphics: Pixar, Dreamworks, EA Games, NVidia, National Labs. AI: BAE, Texas Instruments, Microsoft. Their graphics graduates historically have had a major impact on the film industry. I also received offers for a masters program at Texas A&M (#47 in CS) and the University of Southern California (#20 in CS). One of the main concerns now is the economy and jobs. If I did a masters degree, there is a chance I could perform my current job part time remotely while pursuing the masters degree. As for the PhD it can be useful for becoming a researcher in some companies.