Given this example http://openlayers.org/en/v3.0.0/examples/vector-wfs.js and using BBOX strategy , does it mean it is necessary to use &bbox=' + extent.join(',') part in source URL?
The OpenLayers3 Strategy BBOX strategy says “request new features
whenever the map bounds are outside the bounds of the previously
requested set of features.”
Yes, the &bbox=' + extent.join(',') if required. If you take it out, you will get no wfs features at all. The example is actually somewhat misleading, in that, it calls it a BBOX strategy, whereas in fact it is a createTile strategy, using the BBOX from each underlying tile, as the wfs BBOX. If you look internally at the source code for ol.source.ServerVector you will find a function loadFeatures that calls ol.loadingstrategy.createTile from ol.loadingstrategy which returns the required extents for each tile, which is then used for each wfs call. That is the extent that you see in the extent.join above.
Or to look at it another way, for every call to get an imagery tile, there is a corresponding call to a wfs tile -- which you can verify by looking in the network tab of your browser's dev tools. So, really, this is a tile BBOX strategy, not a view BBOX strategy.
I thoroughly recommend getting local debugging working for OL3 to understand what is going on. You can do that either by loading ol-debug.js, for a non-compressed version of the js, or by setting up a local server, see these instructions
Related
We are currently building an asset tracking widget using Mapbox-GL.
When zoomed in, we show the actual assets, and this works fine.
But, when zooming out, we would like to switch to a cluster view to get a proper overview of how many assets are where.
From my understanding, such layer needs to have a predefined datasource. eg. GeoJson.
Is there any way to feed Mapbox-GL data from live JS data?
The assets themselves are markers, an afaik there is no way to switch from makers to something else.
So I assume we would have to generate the datasource from the data that makes up the markers somehow?
The sources seems to be using URL's for getting the actual data so I'm at loss here,
Can I transform a set of geo points into something that MapboxGL can use as a data source?
It's rather confusing what you are asking, but in general, there is no problem with updating data live.
Create the data source:
map.addSource('assets', { type: 'geojson', data: { type: 'FeatureCollection', features: [] }})
Then update it:
map.getSource('assets').setData({ ... })
I didn't understand what you mean by:
such layer needs to have a predefined datasource. eg. GeoJson.
or
The assets themselves are markers,
or
an afaik there is no way to switch from makers to something else
I've been implementing a chat client in Electron (Chrome) and React. Our top priority is speed. It behooves us, then, to use a virtualized list component (also known as "buffered render" or "window render"). We've explored react-virtualized, react-window, and react-infinite, among others.
One issue all these components have in common is that if supporting list elements of variable heights, the heights need to be known in advance. Now, some chats are very long, and others are very short, so that presents a challenge for us. (Images and video are easy thanks to EXIF data and ffprobe).
So, we're faced with the challenge of measuring heights while also straining to be extremely performant. One obvious technique is to put the elements in a browser container off-viewport, perform the measurements, and then render the list. But that hurts us on the performance requirement aspect. Software like react-virtualized/CellMeasurer (which is no longer maintained by the original author) and react-window make us of this technique, built in to the library, but performance is somewhat slow as well as unreliable. A similar idea that might be more performant would be to use a background Electron Browser window to do the rendering and measuring, but my intuition is that wouldn't be that much faster.
I submit that there must be some solved way to figure out string height in advance, according to word wrap, max width, and font rules.
My current idea is to use a library like string-pixel-width in order to calculate row heights as soon as we get the text data through our API. Basically, the library uses this piece of code to generate a map of character widths [*]. Then, once we know how wide each text, we separate each line when it maxes out the computed max row width, and finally infer list element height through row count. It's going to require a little bit of algorithmic fiddling due to break-word but there are libraries to help with that – css-line-break seems promising.
[*] We would have to modify it a bit to account for all Unicode character ranges, but that is trivial.
Some options I haven't fully explored yet include the python weasyprint project and the facebook-yoga project. I'm open to your ideas!
Using the canvas capabilities to measure text could solve this problem in a performant way.
Electrons canvas text is calculated the same as the regular text, there are some diffrences in rendering though especially in reguard of anti-aliasing but that does not affect the calculation.
You can get the TextMetrics from any text with
const canvas = document.getElementById('canvas')
const ctx = canvas.getContext('2d')
// Set your font parameters
// Docs: https://developer.mozilla.org/en-US/docs/Web/CSS/font
ctx.font = "30px Arial";
// returns a TextMetrics object
// Docs: https://developer.mozilla.org/en-US/docs/Web/API/TextMetrics
const text = ctx.measureText('Hello world')
This does not include line breaks and word wraps, for this feature I would recommend you to use the text package from pixijs, it uses this method already. In addition you could fork the source (MIT licence) and modify it for additional performance by enabling the experimental chromium TextMetrics features in electron and make use of it.
This can be done when creating a window
new BrowserWindow({
// ... rest of your window config ...
webPreferences: {
experimentalFeatures: true
}
})
Now to the part I mentioned in the comments since I don't know your codebase, your calculations and everything should be happening in the Render Process. If that is not the case you definitely should move your code from the main process over to the render process, if you do file access operations or anything node specific you should still do this but in a so-called preload script
it's a additional parameter in the webPreferences
webPreferences: {
preload: path.join(__dirname, 'preload.js')
experimentalFeatures: true
}
In this script you have full access to node including native node modules without the use of IPC calls. The reason I discourage IPC calls for any type of function that gets called multiple times is that it is slow by nature, you need to serialize/deserialize to make them work. The default behaviour for electron is even worse since it uses JSON, except you use ArrayBuffers.
According to the official documentation Recognize and Augment Images
Beginning with ARCore 1.9, if your image will never move from its
position (for example, a poster affixed to a wall), you can attach a
global anchor to the image to increase the stability of tracking.
but no further hints or instructions of how to actually do it in code is given. Please advice.
What they probably meant is to create a normal anchor.
Trackable.createAnchor()
This will force ARCore to keep more data related to that location in memory.
You can create an anchor attached to an image like this:
// Create a new anchor for newly found images.
if (!augmentedImageMap.containsKey(augmentedImage)) {
AugmentedImageNode node = new AugmentedImageNode(this);
node.setImage(augmentedImage);
augmentedImageMap.put(augmentedImage, node);
arFragment.getArSceneView().getScene().addChild(node);
}
break;
See a full example including the above extract in the Sceneforms here: https://github.com/google-ar/sceneform-android-sdk/blob/master/samples/augmentedimage/app/src/main/java/com/google/ar/sceneform/samples/augmentedimage/AugmentedImageActivity.java
Hosting an anchor as a cloud anchor is described in detail in an ARCore code lab - see link here: https://codelabs.developers.google.com/codelabs/arcore-cloud-anchors/#2
It is worth looking at the whole codelab as it is short and clear, but the key line to host the anchor you create is below:
snackbarHelper.showMessage(getActivity(), "Now hosting anchor...");
cloudAnchorManager.hostCloudAnchor(
getArSceneView().getSession(), anchor, this::onHostedAnchorAvailable);
I have downloaded the community samples, installed SDK and run the solution successfully in Visual Studio to use the default add-in. I am now interested in customizing the control to:
1) display specific layers (not all of the active/displayed layers)
2) open to a specified zoom extent.
I have located some of the snippets on the git site (zoom to extent specifically) but do not know how to format the coordinates and am unclear as to what heading they go under. I cannot find related code to mimic and am unfamiliar with coding in C# (pretty well versed in python and AHK). Any help or resources would be GREATLY appreciated. Thanks in advance!
I got this response, for those who are interested:
see thread here
MapControl has a ViewContent property that can be set to any custom view content. In the sample, I am using the MapControlContentFactory.Create method to set the view content (within the InitializeMapControl method in MapControlDockpane.xaml.cs). This Create method has many overloads. This particular overload might be exactly what you need: (Note the first parameter which takes a list of any layers you need)
Create Method: http://pro.arcgis.com/en/pro-app/sdk/api-reference/#topic12607.html
public static MapControlContent Create( IEnumerable layers, Envelope initialExtent, MapViewingMode viewingMode )
MapControl's zoom extent is also defined when you create the content using the Create method (the envelope parameter). In the sample, I am listening to the ActiveMapViewChangedEvent and MapViewCameraChangedEvent events and modifying the MapControl's extent to match that. You can remove that for your workflow and set the MapControl's content the way you want it to be.
The Documentation of OpenCV mentions that "the returned image (by cvRetrieveFrame) should not be released or modified by the user" ...
Link: http://opencv.willowgarage.com/documentation/c/highgui_reading_and_writing_images_and_video.html#retrieveframe
I am trying to debug my code, which involves the following steps:
Retrieve frame from video using cvRetrieveFrame()
Do some processing on the frame
output results
My instinct says that something is wrong with cvRetrieveFrame() because if I manually input frames using cvLoadImage, the program works fine. But I am not getting same results while using cvRetrieveFrame().
Since the documentation mentions such a restriction, any reason for such a restriction ? And, any alternatives ?
Have a great day
Before you call this function, you should have used another function which is cvGrabFrame() in order to be able to use the mentioned function, which you can use it for doing any necessary processing on the frame (such as the decompression stage in
the codec) and then return an IplImage* pointer that points to another internal buff er
(so do not rely on this image, because it will be overwritten the next time you call
cvGrabFrame()).