Why is a custom resolver needed here (AutoMapper)?

Question

Given the following entity model:

public class Location
{
    public int Id { get; set; }
    public Coordinates Center { get; set; }
}
public class Coordinates
{
    public double? Latitude { get; set; }
    public double? Longitude { get; set; }
}

... and the following view model:

public class LocationModel
{
    public int Id { get; set; }
    public double? CenterLatitude { get; set; }
    public double? CenterLongitude { get; set; }
}

The LocationModel properties are named such that mapping from the entity to the model does not require a custom resolver.

However when mapping from a model to an entity, the following custom resolver is needed:

CreateMap<LocationModel, Location>()
    .ForMember(target => target.Center, opt => opt
        .ResolveUsing(source => new Coordinates 
            { 
                Latitude = source.CenterLatitude, 
                Longitude = source.CenterLongitude 
            }))

Why is this? Is there a simpler way to make AutoMapper to construct a new Coordinates value object based on the naming conventions in the viewmodel?

Update

To answer the first comment, there is nothing special about the entity to viewmodel mapping:

CreateMap<Location, LocationModel>();

Answer 1

Edit

Please see comment thread below. This answer is actually for the opposite mapping.

---

You're doing something else wrong. You are following the convention correctly, so the mapping should work without any need for a resolver.

I just tried this test, and it passed:

public class Location
{
    public int Id { get; set; }
    public Coordinates Center { get; set; }
}

public class Coordinates
{
    public double? Latitude { get; set; }
    public double? Longitude { get; set; }
}

public class LocationModel
{
    public int Id { get; set; }
    public double? CenterLatitude { get; set; }
    public double? CenterLongitude { get; set; }
}

[Test]
public void LocationMapsToLocationModel()
{
    Mapper.CreateMap<Location, LocationModel>();

    var location = new Location
    {
        Id = 1,
        Center = new Coordinates { Latitude = 1.11, Longitude = 2.22 }
    };

    var locationModel = Mapper.Map<LocationModel>(location);

    Assert.AreEqual(2.22, locationModel.CenterLongitude);
}