This time, we'll use the GPS coordinates to search in Wikipedia. Confused? Read all about it in this TechTip!
As a follow-up to the previous TechTip, this one will provide the means to complement the Points of Interest (POI) data with geo-referenced Wikipedia articles. GeoNames has a Web service called Find Nearby Wikipedia Entries that works the same as Find Nearby POIs.
Wikipedia is used by millions of people as the reference for…well, nearly everything! You can add your own articles to Wikipedia, providing information about your company, shop, subsidiary, office, or whatever. Tasteful articles paint your company in a favorable light, like in this example. Just try not to exaggerate.
The Web service has the usual simplicity of GeoNames' REST Web services: you provide the latitude and longitude coordinates, and it returns the basic information about the Wikipedia entry along with a link to the complete article. Here's an example: the King of Prussia Mall GPS coordinates (latitude 40.090803 and longitude -75.384999) were used to compose a URL such as the one below:
http://api.geonames.org/findNearbyWikipedia?lat=40.090803&lng=-75.384999&username=demo
That returns something similar to this (I removed all entries but one, in order to keep the example simple):
<geonames>
<entry>
<lang>en</lang>
<title>King of Prussia Mall</title>
<summary>The King of Prussia Mall is the largest shopping mall on the East Coast of the United States, and largest shopping mall in the United States of America in terms of leasable retail space. (...)</summary>
<feature>landmark</feature>
<countryCode>US</countryCode>
<elevation>59</elevation>
<lat>40.0883</lat>
<lng>-75.3914</lng>
<wikipediaUrl>http://en.wikipedia.org/wiki/King_of_Prussia_Mall</wikipediaUrl>
<thumbnailImg/>
<rank>94</rank>
<distance>0.609</distance>
</entry>
</geonames>
The <entry> element is composed of the following sub-elements:
- Lang—The language in which the data will be presented. The default is English, but there are other options. I'll discuss the language later in this tip.
- Title—The title of the Wikipedia entry
- Summary—A 300-character (or less) summary of the entry
- Feature—The type of entry (landmark in this small example, but it could be anything from a railway station to a mountain or a city). See a list on GeoNames Web site for more details.
- CountryCode—The two-character code for the country (more information here)
- Elevation—More or less self-explanatory (more details here)
- Lat/lng—The GPS coordinates of the Wikipedia entry. Please note that these are not the input coordinates.
- WikipediaURL—The link to the full Wikipedia entry
- ThumbnailImg—The link to the thumbnail image related with the article, if one is available (good luck finding one; I couldn't)
- Rank— The rank of the Wikipedia entry, ranging from 0 (worst) to 100 (best)
- Distance— The distance between the input coordinates and the ones related to the Wikipedia entry
As in previous TechTips, I've created a procedure that can be easily called from your program:
If RtvWEFrmGPS(P_Latitude : P_Longitude : P_WE_DS : P_NbrElems: P_ErrCode : P_ErrMsg ) = *Off;
// Use the P_WE_DS array data
Else;
// something went wrong, check the P_ErrCode and P_ErrMsg to know what
EndIf;
(Note: You can find a fully working example in the QRPGLESRC/TST_FNWADD source member.)
P_Latitude and P_Longitude are the input parameters, while P_WE_DS, P_NbrElems, P_ErrCode, and P_ErrMsg compose the procedure's response.
Let's focus on the last four parameters. As a quick glance at the sample code above hints, P_ErrCode and P_ErrMsg are the error code and message, used in case something goes wrong when the procedure is invoked. By "going wrong," I mean a Web service error, failure to access the server (which is usually caused by a firewall issue), or any other issue. There are a few foreseen errors in the source code and a kind of "catch-all" error also.
Finally, P_WE_DS is an array composed of most of the Web service response sub-elements. Why not all, you might ask? Well, I found little use for <thumbnailImg>. It's almost always empty, and this poses a problem: the XML notation used is not fully compatible with XML-INTO (at least not the V5R4M0 version of XML-INTO). The empty tag appears as "<thumbnailImg/>", and this notation causes XML-INTO to fail. I took a shortcut here by deciding to leave the thumbnail URL out of the P_WE_DS array.
Note: Here's a good way to "debug" a failing XML-INTO: remove an element at a time of the data structure that will be receiving the XML.
That's about all regarding this procedure, because its inner workings are similar to the procedure explained in the previous TechTip. Instead, let's discuss possible enhancements to it. Wikipedia contains articles written in 240 languages, and the GeoNames database has geo-referenced articles in about 230 of those. This Web service offers an additional input parameter: the language code. In order to use it, you just have to add "&lang=<languagecode>" to the invocation of the Web service. If you don't specify it, the results will be presented in English. Truth be told, a vast majority of the Wikipedia articles are in English, but there are also relevant quantities of articles in Dutch, French, German, Italian, and Portuguese. So how can you include this extra parameter on the procedure? It's quite simple, actually:
Look for the WEBFORM_setVar… lines in the QRPGLESRC/RTVFNW member and simply add a new WEBFORM_setVar … line with 'lang' and whichever language code you want, 'pt' for instance:
W_Lang = 'pt';
WEBFORM_setVar(W_Form : 'lang' : %Trim(W_Lang) );
You can also use the Postal Code instead of the latitude/longitude as input parameter. In this case, be sure to also add the country code as an input parameter, as you might get results from multiple countries.
As usual, I also provide the complete source code and an example. You can download the save file here.
That's all for now. I hope you have enjoyed reading and that you find my fiddling with REST Web services useful.
Rafael Victória-Pereira has more than 20 years of IBM i experience as a programmer, analyst, and manager. Over that period, he has been an active voice in the IBM i community, encouraging and helping programmers transition to ILE and free-format RPG. Rafael has written more than 100 technical articles about topics ranging from interfaces (the topic for his first book, Flexible Input, Dazzling Output with IBM i) to modern RPG and SQL in his popular RPG Academy and SQL 101 series on mcpressonline.com and in his books Evolve Your RPG Coding and SQL for IBM i: A Database Modernization Guide. Rafael writes in an easy-to-read, practical style that is highly popular with his audience of IBM technology professionals.
Rafael is the Deputy IT Director - Infrastructures and Services at the Luis Simões Group in Portugal. His areas of expertise include programming in the IBM i native languages (RPG, CL, and DB2 SQL) and in "modern" programming languages, such as Java, C#, and Python, as well as project management and consultancy.
MC Press books written by Rafael Victória-Pereira available now on the MC Press Bookstore.
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