What is metadata? How do I create a metadata and how do I associate it to a Cloud target using Vuforia?

问题

I modified sample CloudRecog code for my own code. I created cloud database and get AccessKeys then copied this keys to CloudReco.cpp file. What should i use for metadata. I didn't understand this. Then when i was reading sample code i saw this line: private static final String mServerURL = "https://ar.qualcomm.at/samples/cloudreco/json/". How to get my metaData url?

回答1:

EDIT: this is in response to the first part of your question,: "What should i use for metadata" (not the second part about how to find the URL)

Based on their documentation (https://developer.vuforia.com/resources/dev-guide/cloud-targets):

The metadata is passed to the application whenever the Cloud Reco target is recognized. It is up to the developer to determine the content of this metadata – Vuforia treats it as a blob and just passes it along to the application. The maximum size of the uploadable metadata is 150kByte.

I added some debugging in their CloudRecognition app and saw that the payload (presumably the meta-data) they return when "recognizing" an image is:

{
    "thumburl": "https://developer.vuforia.com/samples/cloudreco/thumbs/01_thumbnail.png",
    "author": "Karina Borland",
    "your price": "43.15",
    "title": "Cloud Recognition in Vuforia",
    "average rating": "4",
    "# of ratings": "41",
    "targetid": "a47d2ea6b762459bb0aed1ae9dbbe405",
    "bookurl": "https://developer.vuforia.com/samples/cloudreco/book1.php",
    "list price": "43.99"
}

回答2:

The Vuforia Cloud Recognition Service enables new types of applications in retail and publishing. An application using Cloud Recognition will be able to query a Cloud Database with camera images (actual recognition happens in the cloud), and then handle the matching results returned from the cloud to perform local detection and tracking.

Also, every Cloud Image Target can optionally have an associated Metadata; a target metadata is essentially nothing else than a custom user-defined blob of data that can be associated to a target and filled with custom information, as long as the data size does not exeed the allowed limits (up to 1MB per target).

Therefore, you can use the metadata as a way to store additional content that relates to a specific target, that your application will be able to process using some custom logic.

For example, your application may use the metadata to store:

a simple text message that you want your app to display on the screen of your device when the target is detected, for example:
    “Hello, I am your cloud image target XYZ, you have detected me :-) !”
a simple URL string (for instance “http://my_server/my_3d_models/my_model_01.obj”) pointing to a custom network location where you have stored some other content, like a 3D model, a video, an image, or any other custom data, so that for each different image target, your application may use such URL to download the specific content;
more in general, some custom string that your application is able to process and use to perform specific actions
a full 3D model (not just the URL pointing to a model on a server, but the model itself), for example the metadata itself could embed an .OBJ 3D model, provided that the size does not exceed the allowed limits (up to 1MB)
and more ...

How do I create/store metadata for a Cloud target ?

Metadata can be uploaded together with an image target at the time you create the target itself in your Cloud Database; or you can also update the metadata of an existing target, at a later time; in either case, you can use the online TargetManager, as explained here:

https://developer.vuforia.com/resources/dev-guide/managing-targets-cloud-database-using-target-manager

or you can proceed programmatically using the VWS API, as explained here:

https://developer.vuforia.com/resources/dev-guide/managing-targets-cloud-database-using-developer-api

How can I get the metadata of a Cloud target when it is recognized ?

The Vuforia SDK offers a dedicated API to retrieve the metadata of a target in your mobile application. When a Cloud target is detected (recognized), a new TargetSearchResult is reported to the application, and the metadata can be obtained using one of these methods:

Vuforia Native SDK - C++ API:        TargetSearchResult::getMetaData()  -  const char*
Vuforia Native SDK - Java API:        TargetSearchResult.getMetaData()  -  String
Vuforia Unity Extension - C# API:    TargetSearchResult.Metadata  - string

回答3:

The MetaData, uploaded along with your image-target in the CloudReco database, is a .txt-file, containing whatever you want.

What pherris linked, as payload from the sample-application, is in fact the contents of a .json-file that the given image-target's metadata links to.

In the sample application, the structure is as follows:

The application activates the camera and recognizes an image-target
The application then requests that specific image-target's metadata
In this case, the metadata in question is a .txt-file with the following content: http://www.link-to-a-specific-json-file.com/randomname.json
The application then requests the contents of that specific .json-file
The specific .json-file looks as the copy-pasted text-data that pherris linked
The application uses the text-data from the .json-file to fill out the actual content of the sample application

来源：https://stackoverflow.com/questions/20185386/what-is-metadata-how-do-i-create-a-metadata-and-how-do-i-associate-it-to-a-clou

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