Tuesday, March 9, 2010

Augmented Reality, iPhone and ArcGIS Server

I am a HUGE fan of Augmented Reality, and one of my favorite applications on the iPhone is Layar. In this post, I will "walk you" through how to setup a simple ArcGIS Layar Point Of Interests (POI) layer and how to expose it through the iPhone application. In addition, I created a small Flex application that will enable you to add POIs to that feature class through a python geo-processor task.

BTW - this is heavily geared to using ESRI desktop and server tools and I'm assuming that you are familiar with these tools.

First, request a developer key from http://dev.layar.com/. This might take a couple of hours to get to you.

So, in the meantime, let's get started. Using ArcCatalog, create a new point feature class called 'Layar' in a geodatabase with the following fields: Title (text), Line2 (Text), Line3 (Text), Line4 (Text), Attribution (Text), Type (Integer), ImageUrl (Text:512).

Import that layer into a map document using ArcMap. Save and publish the MXD as a Map Service. Just to be on the safe side, clear your REST endpoint service directory cache and list the available services. You should now see the new map service and you can now query using REST the newly created 'Layar' layer.

Next, we need to populate this 'Layar' layer. With the Advent of ArcGIS 10, this could easily be achieved using the new FeatureTask endpoint. However, I'm still using a 9.3.X server and I will have to rely on a geoprocessing task to add point features to the Layar feature class. For the sake of simplicity and quick deployment, I decided to implement this GP task using python. So, using ArcCatalog, create a new GP Toolbox and add to the toolbox a new python script. You can download the script from here. Again, I'm assuming that you are familiar with all these tools. This script will have two parameters. The first input parameter should be named 'featureSet' of type 'FeatureSet' and its schema should reference the Layar feature class. The second parameter should be named 'objectID'. It has an output direction and is of type LONG. Basically what the script does; it expects a feature set with one feature. That feature is read using a cursor and placed in memory. Next an insert cursor is created on the Layar feature class and populated with the in memory information and executed. Upon a successful execution, the OBJECTID of the last inserted feature is retrieved and returned back as a parameter. The whole script is surrounded by a try: except: in case of an exception, where a -1 as an OBJECTID value is returned back. Simple but not simplistic :-) Publish this Toolbox, clear the cache and now you should have new GPService task.

To use this GP task interactively, I created a Flex based web application.
This application consists of a side-by-side map and form component enabling the user by zooming and panning to click and define POI coordinates and to populate that POI attributes. By clicking the Save button, the above publish GP task is invoked and upon a successful completion, the map is refreshed to show the newly added POI. The Flex application source code can be downloaded from here.

Now that we have created and authored this Layar information, we need to publish and consume it on the iPhone Layar application. The Layar folks have described in detail the JSON publishing format - http://layar.pbworks.com/GetPointsOfInterest. So what we need now, is a middleware that accepts an HTTP request from an iPhone, convert the input parameters to an ArcGIS REST query, invoke a query task whose URL is the Layar layer URL in the above publish map service, read the ArcGIS JSON response and convert to a Layar JSON response. Easy, eh ? That is why we have computers :-) I accomplished all this using Java Web Application - you can download the source code from here. This web application is basically a servlet that relies on the Apache HTTPClient library for http communication and the Jackson JSON processor library for fast consumption and JSON production. You might wonder why I decided to write this in Java versus say python. well...First, I'm a Java nut. Two, I can whip this up fairly quickly, Three, wanted to experiment with Google Java App Engine so I can be "in the cloud man !" - LOL, last one is just an artifact of the first two - but it is cool ! When the iPhone Layar application requests POI, it does so on a predefined URL (more on this later) with the following HTTP GET parameters, lat: your current latitude location, lon: your current longitude location, radius: the search radius in meters plus other parameters. In this application I'm just decoding lat, lon and radius.

Now that you have an in-the-cloud POI Layar endpoint and assuming that you have gotten your Layar developer key, you can sign in to http://dev.layar.com/ and create your own layer. The form will request a POI URL, enter your in-the-cloud poi servlet endpoint. All of the above was leading this point. I highly recommend that you test your layer using the Layar test page http://dev.layar.com/api20test/layarTestPage/.

To test this on your iPhone, go to "Settings" add add your developer ID and key to the Layar application settings. Launch the Layar application, and you should see your newly published layer.

This is just the tip of the iceberg. There is so much more that you can do, adjust and customize. I just wanted to share this "little" experience with you. Hope you found it useful and tell me what you think.