Finding Entities with the MapPoint Web Service Find APIs - Getting Entities from Latitude/Longitude (Page 4 of 4 )
We have looked at find service methods that take place names and addresses and return the corresponding latitude/longitude and other entity information. To find entity (or address) information for any given latitude/longitude, use the FindServiceSoap.GetLocationInfo; it gives you entity information for any given latitude and longitude. The GetLocationInfo method takes theGetInfoOptionsobject as an argument, along with a latitude/longitude and a data source name as a string. TheGetLocationInfoobject gives you control to decide which entity types you want using theGetInfoOptions.EntityTypesToReturnfield; you also have the option to obtain addresses for a given latitude/longitude (if available) using theGetInfoOptions. IncludeAddressesflag. The following code shows how to use theGetLocationInfo method:
//Create a find service soap proxy
FindServiceSoap findService = new FindServiceSoap();
//Take an example lat long information that you want to
//find using GetLocationInfo
LatLong latlong = new LatLong();
latlong.Latitude = 47.682;
latlong.Longitude = -122.132;
//Define get info options object
GetInfoOptions options = new GetInfoOptions();
//I'm looking only for cities
options.IncludeAllEntityTypes = false;
options.EntityTypesToReturn = new string[] {"PopulatedPlace"};
//Define a field to hold returned
locations
Location[] returnedLocations;
//Call GetLocationInfo with "MapPoint.NA" data source
returnedLocations = findService.GetLocationInfo(latlong, "MapPoint.NA", options);
//Get entity information
for(int i = 0; i < returnedLocations.Length; i++)
{
Console.WriteLine(returnedLocations[i].Entity.DisplayName);
}
When I’m querying for corresponding entities for the latitude/longitude, I limit my query to a city (the entity namePopulatedPlace) using theEntityTypesToReturnfield; it is important to remember that you must set theIncludeAllEntityTypesto false when you request specific entities.
This method is not a direct inverse to theFindServiceSoap.FindAddressmethod, so if you call theFindServiceSoap.FindAddressmethod to obtain latitude/longitude for an address and pass that latitude/longitude to theFindServiceSoap.GetLocationInfomethod, the resulting address won’t match your original address because of the internal representation of the address data; in MapPoint data sources, addresses are stored in address range blocks along the streets, and the interpolation algorithms are used to calculate the address for a given latitude/longitude and vice versa. So, the addresses returned by theFindServiceSoap.GetLocationInfoare approximations of the original address; in fact, this method returns an array of four possible addresses for any given latitude/longitude in increasing order of the distance from the given latitude/longitude.
Please check back next week for the conclusion to this article.
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 This article is excerpted from chapter six of the book Programming MapPoint in .NET, written by Chandu Thota (O'Reilly; ISBN: 0596009062). Check it out today at your favorite bookstore. Buy this book now.
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