I am creating an offline map app for iPhone (Using MKMapKit). It will have a list of countries. If the user selects a country, all tiles will be downloaded and stored on the iPhone. I will use Open Street Map as the maps provider.
(I have read that bulk downloading is forbidden, but given that tiles for a country is pretty small (≈200MB) and that they will only be downloaded once, at least I don't think it's a problem.)
I think I will be using the template URL #"http://c.tile.openstreetmap.org/{z}/{x}/{y}.png" to downloaded the tiles and then store them. My problem is that I don't know how to determine which tiles belong to which country and therefore to determine which to download.
I found this link in another SO answer, but that only allows you to download .pbf files (which I have no idea what it is) and per continent.
First: If you really want to grab all tiles (at all zoom-levels) you should read the OSM Tile Usage Policy again with care. If you just want to download all the tiles once (for your dev environment) you can use existing downloaders that allow you to select the desired country and download them. This will result in a directory with 1000s of small images and might take some days.
The better way would be to setup your own (desktop or server based) tile rendering chain that gives you full control about styling and doesn't stress the community ressources. Please consult www.switch2osm.org for a detailed tutorial on how to setup a server based rendering stack.
This is a problem. Downloading 200 MB of tiles only once is already questionably because it is not just about the traffic, these tiles have to be rendered first. But if I understood you correctly, with your application every user will download these 200 MB.
Instead you should think about downloading raw data (which PBF is) and either render your own raster tiles as already suggested by MaM, or create a vector map as done by other popular apps, like OsmAnd and Navit.
Related
I downloaded and run map-downloader-ios-swift (https://github.com/heremaps/here-ios-sdk-examples/blob/master/map-downloader-ios) project and it worked well. After finished download 1 region package, how do we show that region in mapview without an internet connection? Also is it possible to add routes in that downloaded region in offline mode?
Thank you.
In offline mode, cached map data is used for rendering, routing, searching, etc. So since you have downloaded the map region package of interest, viewing and routing requests related to to this region will be done with the cached data.
Please read this reference (also applicable to iOS):
https://developer.here.com/documentation/android-premium/dev_guide/topics/routing-offline.html
And as stated on the reference page:
There is no guarantee that online and offline routes will be the same as different algorithms are used for online and offline route calculation. Online route calculation is performed on high performance servers, therefore more computationally intensive algorithms are used online, which cannot be used offline. Online route calculation should be preferred and offline routes are expected to be used as backup especially when there is no connectivity.
The new .zif single file format provided by Zoomify Pro seems to have some performance issues. Comparing it to the old file structure it loads the page 3 to 4 times slower and the requests that it sends exceed 50% more (Tested with the same initial image in multiple file formats).
Using the old format is not feasible for out product and we are stuck with over a minute of load time.
Has anyone encountered this issue, and are there some workarounds? The results in the internet and the official site doesn't seem to be of any help.
NOTE: Contacting the vendor hasn't led to anything yet.
Although the official site claims the zif format could handle very large image, I'm skeptical about it because the viewer tries to do everything in Javascript. The performance is entire based on the client's machine. Try opening it on a faster machine and see if it improves.
Alternative solution: You could create Deep Zoom Image tiles by using VIPS library.
More information here:
https://libvips.github.io/libvips/API/current/Making-image-pyramids.md.html
Scroll further down in the article and you'll see this snippet:
With 7.40 and later, you can use --container to set the container
type. Normally dzsave will write a tree of directories, but with
--container zip you'll get a zip file instead. Use .zip as the directory suffix to turn on zip format automatically:
$ vips dzsave wtc.tif mypyr.zip
to write a zipfile containing the tiles.
Also, checkout this tutorial:
Serve deepzoom images from a zip archive with openseadragon
https://web.archive.org/web/20170310042401/https://literarymachin.es/deepzoom-osd-server/
The community (openseadragon and vips) is much stronger over there so you'll get help when you hit a wall.
If you want to take a break from all of this and just want the images zoomable, you could use 3rd party service such as zoomable.ca or zoomo.ca. It’s free and user friendly (upload your image and embed the viewer to your site like Google Map).
ZIF format designer here... ZIF can easily handle monstrous images, up to hundreds of terabytes in size.
Without a server, of course the viewer tries to do everything, it's the only option. As a result, serving ZIF directly from a webserver will not be as performant as using an image server. But... you can DO it. Using Zoomify tile folders, speed will be faster, but you may have hundreds of thousands or millions of tiles to deal with at the server side, and transfers will be horrendously slow and error-prone.
There are always trade-offs.See zif.photo for specification.
I couldn't find resources discussing the difference between the three download methods in the firebase storage documentation and pros/cons of each. I would like some clarification about the firebase storage documentation.
My App
Displays 100 images ranging from 10 KB-500 KB in size on a table view
Will be used in a location where internet connection and/or phone service could be very weak
Could be used by many users
3 methods for downloading from Firebase storage
Download to NSData in memory
This is the easiest way to quickly download a file, but it must load entire contents of your file into memory. If you request a file larger than your app's available memory, your app will crash. To protect against memory issues, make sure to set the max size to something you know your app can handle, or use another download method.
Question: I tried this method to display 100 images that were 10KB-500KB in size on my table view cells. Although my app didn't crash, as I scrolled through my table, my memory usage increased to 268 mb. Would this method not be recommended for displaying a lot of images?
Download to an NSURL representing a file on device
The writeToFile:completion: method downloads a file directly to a local device. Use this if your users want to have access to the file while offline or to share in a different app.
Question: Does that mean all images from firebase storage will be downloaded on user's phone? Does that mean that the app will be taking up a large percentage of the available storage on the phone?
Generate an NSURL representing the file online
If you already have download infrastructure based around URLs, or just want a URL to share, you can get the download URL for a file by calling the downloadURLWithCompletion: method on a storage reference.
Question: Does this method require a strong internet connection and/or phone service connection to work?
Generally, your memory usage should not be affected by the method of retrieval. As long as you're displaying the 100 images, their data will be stored in the memory and should have the same size if they're identically formatted/compressed.
Either way you go with, I suggest you implement pagination (for your convenience, this question's answer might serve as a good implementation reference/guide) to possibly decrease the memory and network usage.
Now, down to comparing the methods:
Method 1
...but it must load entire contents of your file into memory.
This line might throw some people off thinking it's a
memory-inefficient solution, when all it really means is that you
cannot retrieve parts of the data, you can only download the entire
file. In the case of storing images, you probably would want that for
the data to make sense.
If your application needs to download the images every time the users
access it (i.e if your images are regularly updated), then this
method will probably suit you best. The images will be downloaded
every time the application starts, then they'll get discarded when
you kill it.
You stated that a part of your user base might have a weak internet
connection and so the next method might be more efficient and
user-friendly
Method 2
First off, the answers to your questions:
Yes. The images downloaded using this method will be stored on the users' devices.
The images should take up about the same size they're taking on Firebase storage.
Secondly, if you plan to use this method, then I suggest you store a
timestamp (or any sort of marker) in your database for when the last
change to the images occurred. Then, every time the app opens up, do
the following flow:
If no images are downloaded -> download images and store the database timestamp locally
If the local timestamp does not equal the timestamp on the database -> download images and store the new timestamp locally
Else -> use the images you already have, they should be identical to the ones in Firebase storage
That would be the best way to go if your network usage priority is
higher than that of the local storage.
And finally...
Method 3 (not really)
This is not a data download method, this simply generates a
download URL given a reference to the child. You can then use that
URL to download the data in your app or elsewhere as long as the used
app or API is authorized to access your Firebase storage.
Update:
The URL is generated from a Firebase reference (FIRDatabase.database().reference().child("exampleReference")) and would look like this: (Note: this is a fake link that will not actually work, just used for illustration purpose)
https://firebasestorage.googleapis.com/v0/b/projectName.appspot.com/o/somePathHere%2FchildName%2FsomeOtherChildName%2FimageName.jpg?alt=media&token=1a8f83a7-95xf-4d3s-nf9b-99a274927bcb
If you simply try to access that link you generate through any regular web-browser (assuming you don't have any Firebase rule that conflicts with that in your project), you can directly download that image from anywhere, not just through your app.
So in conclusion, this "Method" does not download data from Firebase storage, it just returns a download URL for your data in case you want a direct link.
I'm building a mobile app using Meteor. To allow for offline usage of the app, I want the app to be able to download a large-ish json file while online, then access the data in the json file, written to MongoDB, while offline.
This works fine. However, in the downloaded json file, there are plenty of references to online images that won't display in the app once the app is offline.
So, I want to be able to download (a selection of) the images referenced in the json file to the app, so that the app can access them even when offline.
(Downloading images could happen in the background for as long as a connection is available.)
There's an implementation of imgCache.js available on Atmosphere, which fails to initialize for me.
I suppose it's theoretically possible to individually load each image to a canvas, save the canvas content to MongoDB, then load the content when needed. Info on some of this is here. But, this feels rather convoluted and, if really feasible, I would expect someone to have done this before with success.
How can I do achieve caching of images for offline use in Meteor?
So, you've probably already read this article about application cache.
If the images are static, you can just include them in the manifest. Be sure you understand the manifest and cache expirations (see the article).
If the images are dynamic, you'll find some techniques to store images in local storage
If that's the case, this may be what you want.
I have an application which downloads its product data(descipttions and images) from server and stores them localy to be available offline. For product images I'm using forge.file.cacheURL which works great but on my iPAD, this cache is being cleared during the day when I work with another apps. This causes my application to have only descipription texts available without images and user must connect to internet and synchronize again what is quite annoying. Is there a better way how to implement this scenario?
Have you tried to use the forge.prefs module for this purpose? It allows you so persistantly save key-value-pairs locally (much like HTML5 localstorage). Read more about the exact syntax in Trigger.io's official API documentation.
I'm not quite sure whether its possible to save images with this method, but you could easily transform your images into strings and vice-versa. Check out the second chapter of this post by Robert Nyman on how to save images in localStorage.