Construct DbGeography point from Latitude and Longitude doubles?

41
votes

I want to construct a DbGeography point from latitude and longitude doubles.

I know I can convert my doubles to strings and use the DbGeography.FromText method.

var latitude = 50.0d;
var longitude = 30.0d;

var pointString = string.Format(
    "POINT({0} {1})",
    longitude.ToString(),
    latitude.ToString());

var point = DbGeography.FromText(pointString);

But it seems wasteful to convert my doubles to strings just so that DbGeography can parse them as doubles again.


I tried constructing a DbGeography directly like this:

var point = new DbGeography()
{
    Latitude = 50,
    Longitude = 30
};

but the Latitude and Longitude properties are read-only. (Which makes sense, because the DbGeography class handles much more than individual points)


The DbGeography class also provides a FromBinary method that takes a byte array. I'm not sure how to martial my latitude and longitude doubles into a correctly-formatted byte array.

Is there a simpler way to construct a DbGeography instance out of Latitude and Longitude doubles than the code at the top?

3
entity-frameworkgeospatial
Why don't you create a method public static DbGeography CreatePoint(double, double) which would wrap your code ? It won't avoid conversion, but at least makes your code clearer... – Raphaël Althaus
I'll probably end up doing something like that. It's too bad there aren't static extension methods; I would like to be able to keep all of the static DbGeography create methods under one class. – jcarpenter2
Not that this really helps, but in the version 6+ of C# you can use string interpolation like this: DbGeography.FromText($"POINT({longitude} {latitude})"); – Martin Brown

3 Answers

54
votes

In short, no there isn't.

SqlGeography has an appropriate method:

Microsoft.SqlServer.Types.SqlGeography.Point(latitude, longitude, srid);

... but you would then have to convert to DbGeography anyway. If you are interested in this, see a previous answer of mine on converting: DbGeography to SqlGeography (and back)

That said, I completely agree with Raphael Althaus in that you should create a static method to make your life easier:

public static DbGeography CreatePoint(double lat, double lon, int srid = 4326)
{
    string wkt = String.Format("POINT({0} {1})", lon, lat);

    return DbGeography.PointFromText(wkt, srid);
}

Then all usage can go through that method.

EDIT

@Korayem Made an excellent suggestion that I actually have done myself since originally answering the question. Most people use the SRID 4326 so we can make the static method easier to use by carrying that as the parameter's default value.

0
votes

You can simplify it like this:

  DbGeography.FromText(String.Format(CultureInfo.InvariantCulture, "POINT({0} {1})", longitude, latitude));

for example:

DbGeography.FromText("POINT(-73.935242 40.730610)"),

without using int srid = 4326; which is default value.

If you use it many times use it in a static method:

private static DbGeography CreatePoint(double latitude, double longitude)
{
    return DbGeography.FromText(String.Format(CultureInfo.InvariantCulture, "POINT({0} {1})", longitude, latitude));
}

PS: Don't forget to use CultureInfo.InvariantCulture because you will get an exception for some cultures.

0
votes

Assuming you are targeting SQL Server, you can do it without string parsing. First create a SqlGeography:

var sqlPoint = Microsoft.SqlServer.Types.SqlGeography.Point(latitude, longitude, srid);

Then create a DbGeography from this SqlGeography (see my answer to a separate question about DbGeography conversion).

var dbPoint = System.Data.Entity.SqlServer.SqlSpatialServices.Default.GeographyFromProviderValue(sqlPoint);