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About jkflying

  • Birthday 10/07/1989

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    Cape Town, South Africa

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    LabVIEW 2011
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  1. asbo, ShaunR: How would you suggest I place clusters within clusters within clusters within... (dynamically)? I'm desperate for speed, and if it means sacrificing OOP design I'm willing to try it, but as far as I can tell LV specifies cluster contents pretty rigidly. Doing a prev/next doesn't work in a kd tree because we have a large number of dimensions... and implicit kd trees will give this type of structure but use huge amounts of memory (curse of dimensionality and all that). As you'll see in my project, I've already tried a simple brute force method with a simple array subtract/square/sum/min for finding the nearest point, and if it isn't fast enough with raw arrays it definitely won't be fast enough with clusters. Unless I've completely misunderstood you... sam: The recursive implementation is simply because I can't think of any other way to move into a tree of unknown depth in a data-flow environment without doing a copy of each subtree as we go. Sure,i could use a while loop, but it would be really slow as it would require copying each subtree onto the stack as I go. Aristos Queue Thanks for the feedback. I've gone through and implemented the ideas you've given, excepting the parent_kdtree class, and I've almost doubled my performance, but it's still 50x slower than the .Net. As I'm not really concerned about concurrent access, would you then recommend getting rid of the DVR-on-a-stack technique and instead go for a recursive unbundle/bundle without any DVRs at all then? I thought the casting might be slow so I tried changing the data type in the queue to just straight kdtree DVRs and it slowed me down about 4x. Not sure why, but it seems that is the wrong thing to do. mje: A kd-tree is a tree that works in more than one dimension, ie. for a k-dimensional point cloud. It is typically used for fast nearest-neighbor lookup. Check out http://en.wikipedia.org/wiki/K-d_tree. The one described on Wikipedia isn't quite what I'm using, as I don't store points on lower parts of the tree, just the leaves, and at each leaf I keep an array of points. I also have some optimizations such as keeping track of the hyperrect containing each subtree and only traversing that tree if that hyperrect could contain a closer point. A bit abstract, I know I just tried profiling, and I spend more time in Exemplar:getSqDist than I do in the entire .Net lookup algorithm. So maybe I'll try a C++ .dll instead... sigh.
  2. I am writing a performance-sensitive application which requires the use of a nearest-neighbor lookup. Originally I used a brute-force method, but unfortunately this gets to be very slow as the data size increases . I have a point cloud of ~100k points in 2D, and need around 50k nearest neighbor lookups per second as a minimum performance requirement. As a solution I wrote a kd-tree in .Net and used LabView to call the .Net dll. However, I discovered that each .Net transaction carries with it about a 0.5ms delay. I've tried bunching the data up into groups, but this only helps so much, as I am using an iterative process. Armed with my new-found kd-tree knowledge, I then wrote the kd-tree in LV-OOP, using DVRs for both subtrees and leaf values. However, my LV implementation is still 100x slower than the .Net implementation, and 20x slower than brute force. And this is with just 10k points. I'm fairly new to LV (about 6 months in an academic environment) and I'm fairly sure I've made a massive blunder somewhere, but I don't have any idea what it might be. http://robowiki.net/...d-tree_Tutorial is the tutorial that I used for writing both trees - note that I've only implemented a 1-NN lookup method, so have no need for the priority queue. Just some notes: I found using in-place data structure unbundle-bundle was much faster than using normal unbundle-bundle for all of the read/writes. The tree started out with pure by-value subtrees and data, so was even slower before I changed to DVRs. The lookup uses a queue as a stack, rather than being recursive. Not sure if this is good or bad. The add element uses recursion. Again, not sure if this is good or bad. I've written speed tests for brute force, .Net and LV lookups with names like with test_...... .vi if you want to compare performance. kd_tree Folder.zip Thanks in advance for any help Julian Kent
  3. What will happen for multi-dimensional arrays? Will only one terminal be required?
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