I am trying to export a Sentinel-1 mosaic with the code below. I keep getting this missing data gap between the two images. Even when I export the images separately, and mosaic them myself in ArcGIS, I still have this problem.      var start_date = ee.Date('2019-08-01'); var finish_date = ee.Date('2019-08-15'); var orbit = 'ASENDING';  // Get the VV collection. var collectionS1 = ee.ImageCollection('COPERNICUS/S1_GRD')     .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))     .filter(ee.Filter.eq('instrumentMode', 'IW'))     //.filter(ee.Filter.eq('orbitProperties_pass', orbit))     .filterDate(start_date, finish_date)     .filterBounds(polygons);   // Get the VV collection. var collectionVH = collectionS1.select('VH');  var VH = ee.Image(collectionVH.median());  Map.centerObject(polygons, 7); Map.addLayer(VH, {min: -25, max: 5}, 'VH', true);  //Import Tool var batch = require('users/fitoprincipe/geetools:batch');  // Change Folder Name  var folder = 'GEE_EXPORT';   // Download Collections batch.Download.ImageCollection.toDrive(collectionVH, folder,           {name: 'VH_'+orbit+'_'+'{id}',                scale: 10,               region: polygons,                      fileFormat: 'GeoTIFF',                   maxPixels: 1e13,               type: 'float'});
Some months ago I posted  about exporting Sentinel 1 scenes from a collection and was successful with help from .   I now have a new region of interest, which sits on the overlap between 2 scene footprints (sequential images in descending orbit). When I make a mosaic of the 2 scenes I get a small no data gap and lack of alignment between the 2 images:  // Create a geometry representing an export region. var roi = ee.Geometry.Rectangle([-62.67, -8.31, -63.25, -8.85]); var zoomPoint = ee.Geometry.Point([-62.35, -8.06])  // Load the Sentinel-1 ImageCollection. var sentinel1 = ee.ImageCollection('COPERNICUS/S1_GRD') .filterBounds(roi);   // Filter by metadata properties. var IW_H = sentinel1  // Filter to get images with VV and VH dual polarization. .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VV')) .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))  // Filter to get images collected in interferometric wide swath mode. .filter(ee.Filter.eq('instrumentMode', 'IW'))  // Filter IWs to get High res. .filter(ee.Filter.eq('resolution', 'H'))  // Filter IW-Highs to get 10m res .filter(ee.Filter.eq('resolution_meters', 10));  // Filter to get images from different look angles var col_desc = IW_H.filter(ee.Filter.eq('orbitProperties_pass', 'DESCENDING'));  // Spatially mosaic the images in the collection and display var col = col_desc.mosaic(); var colVV = col.select(0) Map.addLayer(colVV, {min:-17, max:-3}, "VV"); Map.centerObject(zoomPoint, 20);   What am I missing?  Are these scenes not acquired sequentially?
During self-study, I ran across the question of how many ways six numbers can be chosen from the numbers 1 - 49 without replacement, stipulating that no two of the numbers be consecutive.  I can obtain a simple lower bound by saying that, in the worst-case scenario, when you choose a particular number, there are now three numbers that cannot be chosen next.  For example, if I first pick 17, then I can't choose 16, 17, or 18 for the remaining choices.  This gives me the lower bound  $$\frac{49*46*43*40*37*34}{6!} = 6,773,770 \frac{8}{9}$$  This is about 48% of ${}_{49}C_6 =  13,983,816$.  The real answer must be bigger (and an integer).  I haven't found a way to calculate it, though.  The original problem asked to show that the probability of having non-consecutive integers when you choose six is greater than 50%, so if the problem is complicated to count exactly, better approximations that show the answer is above 50% would also be appreciated.   Of course, I can use a computer to do the counting, but I'm interested in learning what methods I'm missing. Create Random Number Sequence with No Repeats Duplicate:    I want an pseudo random number generator that can generate numbers with no repeats in a random order. For example: random(10) might return 5, 9, 1, 4, 2, 8, 3, 7, 6, 10 Is there a better way to do it other than making the range of numbers and shuffling them about, or checking the generated list for repeats?  Edit: Also I want it to be efficient in generating big numbers without the entire range.  Edit: I see everyone suggesting shuffle algorithms. But if I want to generate large random number (1024 byte+) then that method would take alot more memory than if I just used a regular RNG and inserted into a Set until it was a specified length, right? Is there no better mathematical algorithm for this. Rendering smoke in Cycles? Add the ability to add "top questions" to Careers 2.0 Profile Allow me to add my own "top questions" too! I know, I know, the site should be more heavily weighted to answering, but sometimes, how and what people ask is important too! For example I recently asked  which I think is a fairly good question. Clearly I'm going to avoid questions where I've asked something very simple, but I know of a user or two who are implementing their own C standard libraries and the depth of those questions is important/ought to be on show.  Of course, the argument I can just look at their profile holds, but that awesome q/a might have been from a year or so ago in which case finding it is difficult. What does Superman do with his regular clothes after changing in the phone booth? We all know that Superman changes in the phone booth. But where does he put his regular clothes while he's on a mission? He doesn't throw it out, because he changes back. But we don't see him carrying a bag of dirty laundry while he's on a mission.  ("In his right hand, Superman has Lois Lane, and in his left hand he seems to be holding... boxers??)  And I can't imagine he leaves it in the phone booth.  So where does Superman leave his regular clothes after he changes? In short, :     If you go before the Board of   Directors and ask for 1.5 billion   dollars to build a nuclear reactor, no   one will review or discuss the details   of the plant. They will assume that   experts have been over every inch of   the plans, and not want to look   foolish by asking a silly question.      However, if you ask the same group to   approve a 30 dollar expenditure for   lumber with which to build a bikeshed   (presumably a British term for the   smallest possible building) then be   prepared for a 45 minute discussion   about all aspects of the bikeshed,   including the color of the paint. The   explanation for this is that everyone   can grasp the scale of a bikeshed.   To transform this problem to Stack Overflow terms, questions that are trivial such as "How to convert a C string to a QString or "What is the difference between . and ->" get a lot more views, answers and votes than real questions of the form "How do I frob this widget" that bother real professionals. Fewer views mean less possible votes for good answers and hence less incentive for people to answer.  How can Stack Exchange solve this problem? C program to convert Fahrenheit to Celsius always prints zero What are acceptable reasons for flagging as "Requires Moderator attention"? After reading , I feel I don't quite understand this function. What are the guidelines for flagging a question as &quot;Requires Moderator attention&quot;? Custom plugin giving: wp-admin/admin-ajax.php 400 (Bad Request) I am having trouble debugging an issue with a plugin that I'm writing. I want to do an Ajax request when a user changes the option on a select input. The thing is it was fully working as expected yesterday, then when I test the website today (no code changes were made at all since yesterday) I'm getting an:   domain.com/wp-admin/admin-ajax.php 400 (Bad Request)  message in my Chrome console. If I try in Internet Explorer/FireFox it doesn't give the error in console but the Ajax request is still not working.  The plugin I'm creating is on a DigitalOcean droplet which was made using their one click app for WordPress.  Here is the barebones code I'm using on the plugin for the ajax:  //This is in a class' constructor method add_action('wp_enqueue_scripts', array($this, 'plugin_prefix_scripts'));  //PLUGIN_URL is a constant created earlier in the plugin public function plugin_prefix_scripts() { wp_enqueue_script('plugin_prefix_scripts', PLUGIN_URL . 'scripts/frontend_script.js'); wp_localize_script('plugin_prefix_scripts', 'js_object',   array(     'ajax_url' =&gt; admin_url('admin-ajax.php')   ) );   }  frontend_script.js:  $('#plugin-prefix-option-one, #plugin-prefix-option-two').on('change', function() {     var data = {         'action': 'plugin_prefix_page_change',         'option_val': 'some_val',     }      $.post(js_object.ajax_url, data, function(response) {         console.log(response); });   Back in the class:  add_action('wp_ajax_plugin_prefix_page_change', array($this, 'plugin_prefix_page_change'));  public function plugin_prefix_page_change() {     $arr = array(1, 2, 3, 4, 5);      wp_send_json($arr);      //I've also tried wp_die() and no die call at all but same outcome     die(); }   I'm unsure how to debug this further. Any help is much appreciated.  Thanks When is it acceptable to call GC.Collect? The general advise is that you should not call GC.Collect from your code, but what are the exceptions to this rule?  I can only think of a few very specific cases where it may make sense to force a garbage collection.   One example that springs to mind is a service, that wakes up at intervals, performs some task, and then sleeps for a long time. In this case, it may be a good idea to force a collect to prevent the soon-to-be-idle process from holding on to more memory than needed.   Are there any other cases where it is acceptable to call GC.Collect? What is the difference between linear equation and linear regression? I am using linear equation to find the correlation of values of x, y and z  3x + 4y + 2z = 6 4x + 1y + 4z = 17 8x + 2y + 5z = 9   I would like to know the difference between linear equation and linear regression. Is it the same in approach? Flying EU to UK to EU. Can I get duty free alcohol? On the 20 of March this year I will be flying from Ireland to the UK and then on the another EU country.  Can I buy duty free alcohol (as in alcohol with no tax) leaving the UK ? Display data from geoserver on click map with openlayers I tried to display data with popup from Geoserver or Postgres to my map, but it dosen't work at all. Can anyone please help me? I used this code:      function Info(e)          {                 if (e.features &amp;&amp; e.features.length)                  {                      //console.log(e.features[0].attributes);                     var popupId = e.xy.x + "," + e.xy.y;                     var popup = popups[popupId];                     if (!popup || !popup.map) {                     popup = new OpenLayers.Popup.FramedCloud(                     popupId,                      map.getLonLatFromPixel(e.xy),                     null,                     " ",                     null,                     true,                     function(e) {                         delete popups[this.id];                         this.hide();                         OpenLayers.Event.stop(e);                     }                 );                 popups[popupId] = popup;                 map.addPopup(popup, true);                 }                popup.setContentHTML(popup.contentHTML + "nom_user:" +e.features[0].attributes.nomservice +" region_user :"+ e.features[0].attributes.region);             popup.show();                                    }       selectcltr = {         click: new OpenLayers.Control.WMSGetFeatureInfo({             url: 'http://localhost/geoserver/wms',              title: 'Identify features by clicking',             layers: [ser],             queryVisible: true         }),         hover: new OpenLayers.Control.WMSGetFeatureInfo({             url: 'http://localhost/geoserver/wms',              title: 'Identify features by clicking',             layers: [ser],             hover: true,             // defining a custom format options here             formatOptions: {                 typeName: 'projet',                  featureNS: 'http://www.openplans.org/topp'             },             queryVisible: true         })     } Ownership of .Xauthority transferred to root Somehow, while playing around with LightDM and Webkit Greeter, the ownership of the .Xauthority file in my home dir was given to the root user and I couldn't login because I hadn't the privilegues to lock the file.  I was able to regain ownership of the file and I could login again. (After several hours of reinstalling LightDM and it's greeters)  So now everything's working fine again. But I'd like to know how this happened. Is this a bug in LightDM or Webkit Greeter or something else? Seedable JavaScript random number generator On-screen keyboard popping up whenever I touch screen I'm in 17.10. Whenever I touch the screen, whether to change windows/apps, scroll within a browser, or press a button, the stupid little keyboard pops up in the bottom left corner.  I have never left Screen Keyboard enabled in Universal Access, but if I toggle it on, that's the same keyboard popping up in the bottom left corner.    In this screenshot, I'm simply touching the screen in a full-screen youtube video. You can see the menu pop up on the right, under the point where I'm touching.  I don't have a before pic, but it was similar look/color keyboard, but it was smaller, maybe half as wide, and only in the bottom left section of the screen, as opposed to stretching across the entire width. This change from little left-hand keyboard to full-width keyboard happened after following @pomsky 's advice below.    This is a . You can mark yourself affected by it to hopefully increase its received attention. I get this error message   NMI watchdog: BUG: soft lockup - CPU#2 stuck for 23s! [plymouthd:305]    on the startup of my system (even with live-cd).  My PC is a dell inspiron 7559 with intel graphic and nvidia.  UPDATE - this issue also happens when attempting to install ubuntu 18.10 using LiveUSB How to "find and replace" in a PDF on OS X? vertical alignment of text in tikz node The output from the following script \documentclass{article} \usepackage{tikz} \usepackage{graphicx} \begin{document} \begin{tikzpicture}   \node(title)[text width = 0.25\textwidth, text height = 3 cm, draw]{title};   \end{tikzpicture} \end{document}  is  How can I vertically align the text in the node? Specifying the text depth as in \node(title)[text width = 0.25\textwidth, text height = 1cm, text depth = 1 cm, draw]{     title line 1\\     title line 2\\     title line 3};  Does not result in the text being vertically centred. Web service - current time zone for a city? Is there a web service of some sort (or any other way) to pull a current time zone settings for a (US) city. For the parts of the country that don't follow the Daylight Saving Time and basically jump timezones when everyone else is switching summer/winter time... I don't fancy creating own database of the places that don't follow DST. Is there a way to pull this data on demand?   I need this for the database server (not for client workstations) - there entities stored in the database that have City, State as properties. I need know current timezone for these entities at any moment of time.