I'm trying to calculate the size of an object in pixels in an image, when I have these information:  x * y = the size of the real object in meters q = the quality of the image in ppi d = the distance between object and the camera in meters   Do I have to know the size of image as well? If so, how can I calculate the size of the object in pixels?  I don't know if I need to use the crop factor, sensor size, etc.
If I took a picture of a windmill on the horizon — given that I know the sensor size and the focal length of the lens and other factors to do with the shot — could I calculate how far away an object is from the photographer?
Salesforce REST API authentication? I feel like this should be really easy to do, but I can't find anything about it on the web. Is there a way, through either javascript or a java web servlet, to skip the subsequent authentication?  We are trying to use the REST Api in production, but the problem is, that each time you refresh the page in javascript, or delete the cookies in java, you have to login again to salesforce.  Is there some way to do an ajax call or the login in the background or whatever, so that you can have your application connecting to salesforce right away? Google Sheets has several import functions   IMPORTDATA IMPORTFEED IMPORTHTML IMPORTXML   Sometimes the above functions returns errors like #N/A Imported content is empty and would like to be sure that there isn't a problem with the resource content to be imported.  How do I know if these functions are able to get the content that I looking to import?  I know that there also exist IMPORTRANGE but that function only is able to import content from Google Sheets spreadsheets How do I sort a list of dictionaries by a value of the dictionary? I have a list of dictionaries and want each item to be sorted by a specific value. Take into consideration the list: [{'name':'Homer', 'age':39}, {'name':'Bart', 'age':10}]  When sorted by name, it should become: [{'name':'Bart', 'age':10}, {'name':'Homer', 'age':39}] I've tried to read and understand this:   As a test, since my layout is "Polish, programmer" in the /usr/share/X11/xkb/symbols/pl file I played with remapping the 'q' character to 'x', and it worked just fine.  But what I want, is to remap LWIN (Left Super) to Left Control.   So I tried this: I started editing /usr/share/X11/xkb/symbols/pc file, assuming this is the 'root' of all the other files. Commented out this line:  //key &lt;LWIN&gt; {  [ Super_L       ]   };   and added this one:  key &lt;LWIN&gt; {    [ Control_L     ]   };   and rebooted PC, with no success. I.e. LWIN + C, doesn't copy selected text in text editors to clipboard, instead it just produces the 'c' letter. In the terminal instead of stopping current programm it also just produces the 'c' letter.  Here is my config file:   When I try the xev command and then press the Left Control Key, I see this:  KeyPress event, serial 40, synthetic NO, window 0x5a00001,     root 0x7e, subw 0x0, time 1053321, (374,-259), root:(374,545),     state 0x0, keycode 133 (keysym 0xffe3, Control_L), same_screen YES,     XKeysymToKeycode returns keycode: 37     XLookupString gives 0 bytes:      XmbLookupString gives 0 bytes:      XFilterEvent returns: False  KeyRelease event, serial 40, synthetic NO, window 0x5a00001,     root 0x7e, subw 0x0, time 1053425, (374,-259), root:(374,545),     state 0x0, keycode 133 (keysym 0xffe3, Control_L), same_screen YES,     XKeysymToKeycode returns keycode: 37     XLookupString gives 0 bytes:      XFilterEvent returns: False   BTW. Ask ubuntu suggests me two links to similar questions, but they are old, and suggest using xmodmap, and afaik it's no longer correct answer on Ubuntu >= 16.04 (Xenial) and this is precisely the version I have.  BTW2. I would really like to avoid using apps like Xbindkeys, considering there is a built in solution, which I guess I almost understand, and already spent some time on trying to understand it. Hyperlinks clicked in evince document viewer are not opening, any ideas on how to fix? As it was instructed in another thread here in the forums, I opened the /usr/share/applications/mimeinfo.cache file to check for correct references. And noticed this doesn't seem to be the problem, there even are 3 optional browsers to use.  x-scheme-handler/http=google-chrome.desktop;chromium-browser.desktop;firefox.desktop; x-scheme-handler/https=google-chrome.desktop;chromium-browser.desktop;firefox.desktop;   I already checked that the programs are correctly named, using the "which" command in the terminal, like this:  $ which google-chrome $ /usr/bin/google-chrome   So google-chrome should be the first option and yet the order to open a url doesn't seem to be arriving to the program, not even to the 2nd or 3rd option for that matter anyways.  Also, the 'Get help online...' command in the 'Help' menu doesn't work. So it is not a problem with the specific document file either.  I'm running Ubuntu 12.04 LTS. If you need to ask for more relevant details, please do. It would be nice to have various opinions on how to solve this, thank you :-)  UPDATE: I ran evince from the terminal as asked. This is what I'm getting when trying to open a link:  /opt/google/chrome/google-chrome: line 42: /opt/google/chrome/chrome: Permission denied /opt/google/chrome/google-chrome: line 42: /opt/google/chrome/chrome: Success   Should I try the fix you suggested even if my error log is different?  UPDATE: Tried @maggotbrain's solution and BINGO, now I can study pdf references faster thanks to you bro! I understand the purpose of up/downvoting answers -- some answers are better than others, some answers may be wrong, .etc.  With regard to questions, though, there are other mechanisms to deal with "bad" questions:  comments, close, flag.  A poorly written question should be improved.  A bad question should be closed/deleted.  Often, though I see poorly written questions downvoted. I'm not sure what this accomplishes.  I get loss of rep for offensive or spam questions, but for an off-topic question?  or one that is just poorly written?   Why?  It seems to me that rep ought to be based more on answers on a site of this type.   Fundamentally, it seems that rep ought to be based on what you add to the site, not what you ask of it.  A particularly good question does add to the site, but a poor question doesn't really detract from it in the same way that a bad (wrong) answer does. Sure, go ahead and give people more rep for asking a particularly good question, but why punish people for asking bad questions when there are other ways of handling that.  Why not handle questions more like comments and allow upvotes, but not downvotes?  It seems to me that many, if not most, of the downvoted questions are first timers.  It's more likely that your first introduction to the site will be in asking a question, rather than answering. There is a significant risk to alienating new users when their questions are downvoted -- there's a visceral response to seeing that negative number next to your question.  Why not let the close/flag system weed out questions that don't belong and the comment system work to improve poorly worded questions. Why is my ethernet interface called enp0s10 instead of eth0? When I run ifconfig -a, I only get lo and enp0s10 interfaces, not the classical eth0  What does enp0s10 mean? Why is there no eth0? Simple Past vs. Present Perfect: "was" vs. "has been" Possible Duplicate:          As a English non-native speaker it is difficult for me to understand when I must use present perfect or past simple because in my official language there isn't the present perfect tense. I know that present perfect is related to something that happened in the past but its result is important now. But for instance:        The message has been sent.   The message was sent.      Please help me point me out any examples/contexts where I should use 1. instead of 2. The following identity is true for any given $x \in [-1,1]$: $$\arcsin(x) + \arccos(x) = \frac{\pi}{2}$$  But I don't know how to explain it. I understand that the derivative of the equation is a truth clause, but why would the following be true, intuitively?  $$\int^{x}_{C1}\frac{1\cdot dx}{\sqrt{1-x^{2}}} + \int^{x}_{C2}\frac{-1 \cdot dx}{\sqrt{1-x^{2}}} =\\  \arcsin(x) - \arcsin(C1) + \arccos(x) - \arccos(C2) = 0 \\  \text{while } \arcsin(C1) + \arccos(C2) = \frac{\pi}{2}$$  I can't find the right words to explain why this is true?    Edit #1 (25 Jan, 20:10 UTC): The following is a truth clause: $$ \begin{array}{ll} \frac{d}{dx}(\arcsin(x) + \arccos(x)) = \frac{d}{dx}\frac{\pi}{2} \\ \\ \frac{1}{\sqrt{1-x^{2}}} + \frac{-1}{\sqrt{1-x^{2}}} = 0 \end{array} $$  By integrating the last equation, using the limits $k$ (a constant) and $x$ (variable), I get the following:  $$ \begin{array}{ll} \int^x_k\frac{1}{\sqrt{1-x^{2}}}dx + \int^x_k\frac{-1}{\sqrt{1-x^{2}}}dx = \int^x_k0 \\ \\ \arcsin(x) - \arcsin(k) + \arccos(x) - \arccos(k) = m  \text{ (m is a constant)}\\ \\ \arcsin(x) + \arccos(x) = m + \arcsin(k) + \arccos(k) \\ \\ \text{Assuming that } A = m + \arcsin(k) + \arccos(k) = \frac{\pi}{2} \text{ ,for } x \in [-1,1] \end{array} $$ Using Calculus, why is that true for every $x \in [-1,1]$?    Edit #2:  A big mistake of mine was to think that $\int^x_k0 = m \text{ (m is const.)}$, but that isn't true for definite integrals.  Thus the equations from "Edit #1" should be as follows: $$ \begin{array}{ll} \int^x_k\frac{1}{\sqrt{1-x^{2}}}dx + \int^x_k\frac{-1}{\sqrt{1-x^{2}}}dx = \int^x_k0 \\ \\ \arcsin(x) - \arcsin(k) + \arccos(x) - \arccos(k) = 0\\ \\ \arcsin(x) + \arccos(x) = \arcsin(k) + \arccos(k) \\ \\ A = \arcsin(k) + \arccos(k) = \frac{\pi}{2} \text{ ,for } x \in [-1,1] \end{array} $$ Using Virtual Box, how can I install an OS to a secondary, physical disk, and boot it in both (at separate times) Virtual Box, and as a typical secondary OS install? Here is what I'd like to achieve in QGIS.   Is there a processing tool to remove the overlapping part of polygons?    It is also very important that they do not get merged during the process and that they keep their original attributes since I need to work with them afterwards. Samsung netbook NP300E5A dimming on battery My Samsung netbook NP300E5A screen is continually dimming.  The screen is forty percent dim on battery, but if I plug in the charger, the screen will be normal. I have tried all I know and I could not fix it. What should I do? what am trying to explain  is that the system is dimming like flooricent light  the screen resolution systems are all ok. When I pluging my charge the dimming we stop but when is on battery it look like flashing someone  light when driving The vast majority of intelligent species in the Star Trek universe are bipedal, humanoid creatures.  From the lot I've seen of TOS, TNG, DS9, Voyager, Enterprise, and the movies, it seems that this coincidence goes largely unquestioned.  Metaknowledge grants that it is much easier to have human actors portray human-like beings, and so this was probably done due to budgetary/technological limitations.  However, I'm wondering if an in-universe reason for this was ever given or explored? Make it clearer when looking at a question if I've already voted to close it Since "" we now have the possibility to retract close votes.   However, as mentioned in "" there is no indication when looking at a question to see if I have already cast such a close vote.  Therefore, could we have a UI improvement to show this? Adding some image with freehand circles to improve visibility. Sums and products of algebraic numbers How does one go about proving that the sums and products of two algebraic numbers over a field $F$ (say $a,b\in K$, where $K/F$ is a field extension) is also algebraic?   If we call $f_a$ and $f_b$ the min. poly's of $a$ and $b$, then I'm assuming the answer involves such polynomials. Perhaps looking at their roots in splitting fields for both of them? And finding a "big" splitting field, constructed from those two other ones?      In particular, I'd like a way of explicitly constructing the minimal polynomials $\ f_{ab}$ of $ab$ and $f_{a+b}$ of $a+b$.     I read somewhere that $g(x)=\Pi_j\Pi_i (x-\alpha_i\beta_j)$ works for $ab$, where the $\alpha_i$ and $\beta_j$ are the roots of $f_a$ and $f_b$, respectively, but I do not know why $g(x)\in F[x]$.  Similar remarks for $a+b$ What happens when my aasimar Celestial warlock has overlapping class and racial features? If you are an Aasimar warlock whose otherworldly patron is The Celestial, you will know the light cantrip from both race and class. Additionally, once you reach 6th level in warlock you will have resistance to radiant damage from both race and class.  Is there any ruling on what happens when you have overlapping class and race features? What does a "real" quantum computer need for cryptanalysis and/or cryptographic attack purposes? The cryptographic world has been buzzing the word "quantum" for a while now (even the NSA is currently preparing itself for a post-quantum crypto world) and quantum-related hardware engineering is evolving constantly. For example: the 5-qubit quantum computer created at MIT by using the technique of ion traps succeeded in prime-factorizing 15. Does that mean that since it succesfully managed that, that it is a all-purpose quantum computer which could be used for cryptanalysis and/or cryptographic attacks?   If that's not the case, what exactly would a "real" quantum computer need (think: rough description of expected technical abilities, aka specs) to enable its users to use it for cryptanalysis and/or cryptographic attack purposes? And - ignoring rumours about potentially existing but confidential governmental projects - does any such system already exist today? What was the origin of Star Trek's Borg? Apt-get 403 Forbidden, but accessible in the browser Attack moving or Attack Canceling I watch streams sometimes and i see the high elo Ranged AD move between each shot. Do they gain anything with this? And if so whats a good way to practice it.