I have been doing some tests with the path loss formula and it gives me some pretty good results so far. However, I looked at the original code and saw that the formula used is
distance = Math.pow(10.0, ((-adjustedRssi+txPower)/10*0.35))
where adjustedRssi is RSSI - adjustment. This was giving me very small values for distance so I thought that I must have modified it at some point by accident. After doing the maths and playing around a bit I found that using txPower-adjustment instead of txPower-adjustedRSSI gives me correct distances.
I figured that the error must have been my fault but looking back at an original copy of the library I am seeing that the formula was actually this way all along.
Is this a mistake or am I missing something obvious? Using the formla as is right now gives me wrong results while modifying it the way I did gives right results.
Also, why is the formula only used if the ratio<1. Shouldn't it work in either case?
Yes, you are absolutely right! Reviewing this now, I can see that this was a simple coding error I made when I originally wrote this. I paused work on the path loss formula because I was getting poor results, probably because of this error.
Since this is a development branch of an open source library hosted on Github, it is probably most appropriate to discuss this in that forum. Please feel free to comment directly on the pull request thread here: https://github.com/AltBeacon/android-beacon-library/pull/251. As the lead developer on that project, I would also welcome a pull request with the changes you are making.
Related
I am trying to get the Quickchart Wordcloud API to work, however, I get very spread apart and small text.
This used to work fine (I tested it a few weeks ago), but something seems to have changed to cause the issue you can test below.
Example
Apart from the text, you can see the querystring below:
rotation=0&format=png&height=176px&width=506px&font-family=sans-serif&removeStopwords=true&text=
Any insight into how I can get this to work would be appreciated.
I maintain this API and want to apologize for the trouble you encountered over the last few weeks. This should be fixed now with no action required on your end.
Some background on the trouble: the underlying library, d3-cloud, is a bit finicky and under certain conditions it will not show top words if they are too large. We attempt to resolve this by sizing the words explicitly, but this can be imprecise because we do not have full rendering information. In the long term, I'd like to move to a more robust rendering library but for now we're tuning the workaround.
Related issues in the d3-cloud repo:
https://github.com/jasondavies/d3-cloud/issues/166
https://github.com/jasondavies/d3-cloud/issues/159
https://github.com/jasondavies/d3-cloud/issues/36
Working from the tutorials I wanted to try PID-controlling a second order linear system. I'm running into segfaults when simulating the closed loop. I've put my code over on Gist. It is mostly identical to the example in the dynamical systems tutorial.
Here's what works
Simulating a diagram containing only the second order system
Dropping in PendulumPlant for the second order system and using the controller
Every step up to simulator.AdvanceTo - that's where the segfault occurs
I'm sure I am missing something obvious here. Does anyone with more experience see what's wrong?
Thanks for reporting this. I didn't see anything on quick inspection. I ran your code (both on linux and mac) and was able to reproduce. Absolutely you should never see a silent segfault, so this is a real issue.
I've escalated it here: https://github.com/RobotLocomotion/drake/issues/12497
FTR - I've also opened a PR to improve the PidController documentation. https://github.com/robotlocomotion/drake/pull/12496
I'm investigating this now -- I've also successfully reproduced the bug locally using the provided python, but I've also reproduced it directly in C++. [Reproduced in now defunct branch]
I'll update when I have something concrete.
Update 1: You've got an algebraic loop in these two systems (one that does not exist for the PendulumPlant as its derivatives and output are expressed in terms of its state and not its inputs). In this case, both systems' outputs depend directly on their inputs so, kablooie! The bug, in this case, is figuring out why that isn't communicated to you right up front.
Presumably, you'd also like to know what the right version of this program is that doesn't have an algebraic loop. Stay tuned.
Final update
A patch has gone through to correct the underlying bug. Depending on how you're accessing Drake, it's immediately available in master, or you can wait for the next binary (as to your taste).
Thanks for bringing this issue to our attention.
I am working with the Persee 3D camera from Orbecc. I am currently having problems with the processing of the bag files. Someone has provided some code here: https://github.com/JaouadROS/bagtodepth. I tried looking over this and I can't quite make heads or tails of this. I really only have two main questions:
1: Where is the output being saved to? Will it be saved into one of his directories or will it be output somewhere else?
2: Is the output a sort of stream or will it just convert the data to a certain point?
I have successful downloaded (catkin_ws directory) and ran the program with the Persee, but it doesn't help if I can't access the output. I am looking to access this matrix in real time and was hoping I could just adapt his code to my project. He does mention something about information being stored at depthclean. Sadly, the guy that has posted this has not replied to any of the messages that I have sent. Thanks!
I have tried to implement the ellipse fitting algorithm descibed in the following paper: “ElliFit: An unconstrained, non-iterative, least squares
based geometric ellipse fitting method”, by Prasad, Leung, Quek. A free version can be downloaded online from http://azadproject.ir/wp-content/uploads/2014/07/2013-ElliFit-A-non-constrainednon-iterative-least-squares-based-geometric-Ellipse-Fitting-method.pdf
The authors did not provide any publicly available implementation.
I have implemented the algorithm in Mathematica, I believe I have implemented it correctly, yet it fails to correctly find the fit parameters. The PDF of the experiment can be downloaded here: http://zvrba.net/downloads/ElliFit-fail-example.pdf
Did somebody else try to implement this particular algorithm and, if yes, what is the key to get it working? Is there a "bug" in the paper? Can somebody take another look at my implementation and see whether there's a bug there?
I know it's been almost a year since this question, but it seems that the authors have now provided public source code for ElliFit, both a MATLAB version and an OpenCV version.
Both are available on the the author's homepage. In case the homepage goes offline for some reason, both source codes are shared on Google and are available here (MATLAB) and here (OpenCV).
At the time of writing, I have not personally tested their code, but am planning to use them for a project. I will post any updates here in the next few days.
EDIT:
I got around to test the code sooner than I expected. I gave the OpenCV code a try. It works pretty well, as demonstrated by the image below (ignore the "almost-closed-ellipses". It's an artifact caused by something else in my code).
As you can see, it works pretty well, most of the times. There are some failure cases too (the small ellipse on the spray bottle next to the cup).
I have tried to use this snippet of code
https://code.msdn.microsoft.com/windowsdesktop/Net-Implementation-of-a-d3ac7b9d
to implement a heap-based implementation of Prim's algorithm to solve the Minimum Spanning Tree (MST) problem in a non-directed connected graph.
after a few iterations, i find that the heap/priority queue is not well maintained anymore.
that is the head of the PriorityQueue doesn't have the lowest Key in the Heap.
PQ 0 [-7230, 309]
...
PQ 146 [-7277, 308]
Has anyone use this code and experienced similar problems ?
I can post a link on GitHub if anyone would be looking at it
My needs are for a heap datastructure which supports deletion of an element in the middle. It looks like Fsharpx.collections doesnt have such a data structure.
does anybody know a good implementation available somewhere ?
thanks
Recently, I ported a MaxHeap from PLINQ to F# here and made it MinHeap. It is array-based and performs much better than any "pure functional" alternative.
However, after a lot of benchmarking, I found that SortedDeque based on just a simple sorted circular buffer performs significantly better on most use cases even when I need to add or delete in the middle.
My answer is inspired by V.B. but here it is in full
I have used another library than FSharpx.collections, it is called
Spreads
read that page for details and instructions.
SortedDeque is the data structure i need for this problem.
I used the same code, just changing from the microsoft blog page code to the library functions and found the good result, so it is indeed some bug in the microsoft blog page code
PS. this spreads library has been designed to format financial data for quantitative analysis and i'm happy i found it !!! IT looks like this library is rather recent and thats why its not on top of Google's search or referenced in any other SO question (or if it is i didn't see it)
FSharpx.Collections is of no use for that problem as you can see from that discussion heap issue in FSharpx.Collections