GrassGIS process for DTM of UAV point cloud Using grassGIS I am attempting to produce a DTM (remove buildings and vegetation) from the las point cloud. Unfortunately the point cloud exported from  does not distinguish first and last pulses so the method based on  does not work.    I need an alternative method/tool particularly for removing buildings?  Any recommendations to transform the z-values relative to the drone take-off location to absolute ones (e.g.: sea-level,..)?
Determining bare earth DEM from unclassified LAS file? I have data in LAS format with RGB values created from aerial photogrammetry using a UAV. I am  trying to find a solution to extract the bare earth DEM from the point cloud.   I have tried SAGA, Fusion, MCC-LIDAR, but it is seems they need the LAS file to be already classified (which it naturally isn't). Can anyone point me in the right direction with a brief explanation of the process?   Generally, I would need to process about 100 mill points at a time (can tile them if needed).
Why is usable RAM less than total RAM? My girlfriend bought a laptop last week. It's a core 2 duo with 4 GB  We installed vista 64bit, and one of the first things we did was right click on "My computer" to see gthe properties. Immediately we noticed something strange about her RAM, the line said: Installed memory (RAM): 4,00 GB (3,68 GB usable)  I told her not to worry, thinking it must be something about the laptop hardware (considering her vista installation came from the same DVD as mine, and I never noticed anything like that on my 4 GB desktop). One hour ago, it got worse. We looked at Properties again, and it now says: Installed memory (RAM): 4,00 GB (2,98 GB usable)  What does that mean? Are those 1,02 GB missing or being used by the system?  EDIT: There is a possibility that the sytem information is wrong. I just noticed that it reports an intel T6500 processor, when it's actually a T6400.  How can I find out how much RAM is really available to the system?  EDIT2: Checking the resource monitors, it says 1003 MB are reserved for the hardware. Is that good or bad? Thanks Question: Let $a, b \in \mathbb{R}$ with $a &lt; b$ and let $f: [a,b] \rightarrow [a,b]$ continuous. Show: $f$ has a fixed point, that is, there is an $x \in [a,b]$ with $f(x)=x$.  I suppose this has to do with the basic definition of continuity. The definition I am using is that $f$ is continuous at $a$ if $\displaystyle \lim_{x \to a} f(x)$ exists and if $\displaystyle \lim_{x \to a} f(x) = f(a)$. I must not be understanding it, since I am not sure how to begin showing this... Should I be trying to show that $x$ is both greater than or equal to and less than or equal to $\displaystyle \lim_{x \to a} f(x)$ ? How do I make a table row on a web page look draggable? I have a table on a web page where I need to let the user reorder the rows. I was thinking of letting the user drag the rows to reorder them. But how would I let the user know that he could do that? Should I make an empty cell as the first column with dots or vertical lines like gmail has for each email in the inbox? Where can I get an image like that? Do I use a "grabbing hand" icon for the cursor or a "move" cursor? Do I show the cursor while hovering over the table or just the "grab area"? Do I let the user grab any part of the row to drag? Sigmoid vs Relu function in Convnets How does Earth's interior dynamo work? I'm interested in getting a basic physical understanding of how Earth's magnetic field is generated. I understand that it's a "dynamo" type of effect, driven by convection currents in the molten outer core. These currents cause charges to move, and this generates the field.  However, what I can't find a good explanation of is why there is a separation of charges in the first place. Presumably, moving neutrally charged molten iron would have the same effect as moving any other neutrally charged thing, i.e. it wouldn't create a field.  And presumably, if the fluid wasn't moving then it would become neutral pretty quickly, since molten iron is a good electrical conductor.  So am I right in thinking that the charge separation is the result of positive feedback, in that an intial deviation from neutrality would generate a field, and this would (somehow) cause a greater separation of charges, resulting in a kind of self-maintaining charge separation?  Or is there another explanation?  In either case, does anyone know of a good resource that explains the basic principles in physical terms?  I know that the interior dynamo is a very complex phenomenon, but I'd like something that gives a good physical picture of how the electromagnetic and fluid dynamical phenomena interact, rather than diving straight into partial differential equations. Where can I get images for commercial use? I am running a web site design service for local small business owner. I want avoid legal issues on the images I use. Usually, the images found on Flickr are forbidden for commercial use. Where would be a normal channel to get pictures for commercial use with minimal cost? How can I validate that the picture I used has no legal risk? So, I understand that for a NPN transistor to work the emitter-base junction needs to be forward biased and the collector-base junction needs to be reverse biased.  I understand how current flows from the emitter to the base when forward biased, but I can't seem to wrap my head around how it flows from the emitter, through the base, and into the collector.  From what I understand about the depletion region of a PN junction diode, when forward biased, the electrons in the N-type material are repulsed by the negative charge of the supply (say a battery) and the holes in the P-type material are repulsed by the positive charge from the supply, thus narrowing the depletion region and allowing electrons to flow from the N region to the P region.  I also understand that the holes and electrons are attracted to the source charges when reverse biased, widening the depletion region and blocking any electrons from flowing.  What I don't understand is what happens to the depletion region of the collector-base junction that allows electrons to flow from the emitter to the collector even though the collector-base junction is reverse biased.  Take a simple common emitter circuit for example.  I apparently am not cool enough to post pictures yet so you'll have to use your imagination.  So pretend we have the base connected to the positive terminal on a 1v battery (Vbb).  The collector is connected to the positive terminal on a 10v battery (Vcc).  The emitter and both negative terminals are connected to ground.  Also pretend that there is some kind of current limiting.  How does current get from the emitter through to the collector?  I can see how they are at different potentials, but I don't understand how this overcomes the reverse biasing of the collector-base junction.  Can anyone tell me what actually happens at the junction to allow current flow and how changing Vbb will affect that current? Don't impose delay loading Close dialog when you haven't just loaded it Because of , clicking the "close" link on a question that's been edited (for me usually the edit comes in a half-second before, as I'm reaching for the link) reloads the question instead of opening the Close dialog. Clicking it again to actually open the close dialog says     You may only open the Close dialog every three seconds   I didn't open it, I refreshed the post.  And yes, there are lots of times when the post edit is so trivial it's obvious in less than a second that it doesn't affect the need to close the question. How to find out what init mode system is using? I was looking at this and I'm not sure how to find out which startup service is used on my machine (Ubuntu 14.04 on Digital Ocean). Can it use all of them? (upstart, system v, systemd) How does the /proc//exe symlink differ from ordinary symlinks? If I start a process and then delete the binary of it, I can still recover it from /proc/&lt;pid&gt;/exe:  $ cp `which sleep` . $ ./sleep 10m &amp; [1] 13728 $ rm sleep $ readlink /proc/13728/exe                            /tmp/sleep (deleted) $ cp /proc/13728/exe ./sleep-copy $ diff sleep-copy `which sleep` &amp;&amp; echo not different not different $ stat /proc/13728/exe    File: ‘/proc/13728/exe’ -&gt; ‘/tmp/sleep (deleted)’   Size: 0           Blocks: 0          IO Block: 1024   symbolic link   On the other hand, if I make a symbolic link myself, delete the target and attempt to copy:  cp: cannot stat ‘sleep’: No such file or directory   /proc is an interface to the kernel. So does this symbolic link actually point to the copy loaded in memory, but with a more useful name? How does the exe link work, exactly? ORA-00979 not a group by expression Examples  I've recently found examples of using pairs of enclosing braces {}, with nothing in between the opening and closing braces, as arguments to commands and even to their options:  cat foo | xargs -I{} echo {}  find . -size 0 -exec rm -i {} \;  No Documentation  My problem is that I cannot find a documentation in the  that describes the usage of {} in such context as in the examples above.  I do not think it is a , because a dollar sign must precede the enclosing braces in a parameter expansion as in ${}.  It cannot be a  either, because it takes the form of {x..y[..incr]}, where x and y are not optional.  It also cannot be a  either, because {} is used as arguments.  Questions   What does a pair of enclosing braces {} even mean, in general, as an argument to any command that accepts it? Where can I find a documentation that describes the usage of {} as arguments? How do I remove the Unity launcher? How can we remove the launcher that come with Unity on this new Ubuntu version ? During Winterbash 2014, there was a hat called , which was earned by giving an answer scoring 5 or better to question that had a score of −3 or worse at the time of answering and later rose to a score of +3 or better.  I’ve already shared the . Those cases give me a great deal of confidence that this would be a challenging badge trigger that would produce good behavior with a minor tweak. Here are the Red Barons earned on other sites:    (Logan Maingi) Mathematics  (Mike Miller) Mathematics  (Hugo) English Language and Usage  (tchrist) English Language and Usage  (Mr. Shiny and New 安宇) English Language and Usage  (Darth Satan) Science Fiction and Fantasy  (DVK) Science Fiction and Fantasy  (rolfl) Code Review  (Heslacher and Hosch250) Code Review  (Edward) Code Review  (janos and Manny Meng) Code Review  (Mark Mayo, Rory Alsop and MeNoTalk) Travel      (DJClayworth) Christianity  (McMagister) Puzzling   Looking through the timelines, I’m convinced that the answerer’s votes should be excluded from the pre-answer question score calculation. Doing that would have reduced the number of Red Barons to 16 across the network. However, the cost of making a badge harder to obtain is worth the benefit of avoiding giving people an incentive to manipulate question scores¹.  To wrap up, the hat seemed to have encouraged a number of great answers and rescued some questions that would otherwise have been lost to time. My outstanding questions are:   Were there any problems on questions where people were attempting to earn the hat, but failed? (Or any other problems I didn’t observe.) If not, should we  or create a new badge? If we create a new badge, what should it be called?   I’m especially interested in feedback that counters my own bias in favor of this idea. If I’m missing any problems, I’d like to know about them now.    ¹ Several questions were downvoted, answered, edited (sometimes trivially)  and upvoted by the user who earned the hat. What is the highest power of n in $(n^r-1)!$ where $n$, $r$ are positive integers? The answer supplied is $\frac{n^r-nr+r-1}{n-1}$   The highest power of $n$ in $n^r!  = r +$ the highest power of $n$ in $(n^r-1)!$ as $n^r$ contributes $r$ powers.    So,  the highest power of $n$ in $n^r!$ needs to be $\frac{n^r-nr+r-1}{n-1} + r =\sum_{1≤t&lt;r}n^t $.    This is clearly true if $n$ were prime according to .  Again,  if $r=1$, $\frac{n^r-nr+r-1}{n-1}$ becomes $0$.    But according to , the  highest power of composite $n$ in $(n-1)! ≥ 1 $.  So, the answer does not seem to hold for $r=1$ if $n$ is composite. If $n=\prod p_i^{a_i}$, where $p_i$ are distinct primes,  $n^r=\prod p_i^{ra_i}$  So, the highest power $(q_i)$ of $p_i$ in  $n^r!$ is  $$\sum_{1≤t&lt;∞}\left\lfloor\frac{n^r}{p_i^t} \right\rfloor =\sum_{1≤t≤ra_i}\frac{n^r}{p_i^t} +\sum_{ra_i+1≤t&lt;∞}\left\lfloor\frac{n^r}{p_i^t} \right\rfloor$$  as $p^t|n^r$ for $t≤ra_i$.  So, the highest power of $p_i^{a_i}$ in  $n^r!$ is $\left\lfloor \frac{q_i}{a_i} \right\rfloor=P_i$(say).   So, the highest power of n=$\prod p_i^{a_i}$ in  $n^r!$ is $min(P_i)$  I could not proceed anymore. A site (or scraper) is copying content from Stack Exchange. What should I do? of Stack Overflow, all content posted on Stack Exchange sites by their users (i.e. you wonderful people) has been provided to the whole universe under . For my fellow non-lawyers, that license basically means:   Anyone can use any Stack Exchange posts at any time without having to ask for permission Making money off of the copied content is permitted You don't even have to copy stuff from here verbatim; you can just use it as a starting point and make whatever edits you want There are just two rules you have to follow:   You have to provide . Simple links to the original post and author info are just fine. You have to  and allow other people to use your content, as long as they follow these very same rules. How meta!    (If you ever forget any of that, and want to refresh your memory, the license info is linked to in the footer of every page.)  There are, in fact, a lot of people who republish varying amounts of our content for assorted reasons. Unfortunately, there are some Stack Content Republishers Attributing Poorly and/or Excelling at Ranking (SCRAPERs, for short).  In this context, "attributing poorly" means any use that doesn't follow our attribution rules or make any other reasonable attempt at give credit. This can get pretty egregious; I've seen SCRAPERs that not only don't link back to SE originals, but also use fake author info and post dates to make it harder to find originals. By "excelling at ranking," I'm referring to copycat sites that end up higher in Google results than the original SE sites do for the same content. That's not necessarily wrong, but in some cases, it indicates inappropriate SEO hackery.  So, the question is: what can you do if you spot a SCRAPER? Every finite group is isomorphic to some Galois group for some finite normal extension of some field. How can I measure the actual memory usage of an application or process? This question is covered  in great detail. How do you measure the memory usage of an application or process in Linux? From the blog article of , ps is not an accurate tool to use for this intent.  Why ps is &quot;wrong&quot; Depending on how you look at it, ps is not reporting the real memory usage of processes. What it is really doing is showing how much real memory each process would take up if it were the only process running. Of course, a typical Linux machine has several dozen processes running at any given time, which means that the VSZ and RSS numbers reported by ps are almost definitely wrong. Why is area of a surface of revolution integral $2\pi y~ds$? not '$dx$'? Confidence bands in case of fitting ARIMA in R?