Doing Mathematical calulations in Order by with Linq

Question

I am quite new to Linq to Entity and having some trouble.

Here's my Search repository:

 public static List<Centre> Search(Search search)
 {
    using (var context = new MeetingRoomsContext())
    {
        var query = context.Centres
                .Include("Geo")
                .OrderBy( NEED HELP WITH THIS PART )

        return query.ToList();
    }
 }

I am getting a search object which contains co-ordinates like this:

Search.LongLat = "(-6.265275, 53.334442)"

I need to break that out and do some maths against the co-ordinates in the DB in order to order results by the closest to the searched point for first.

In mathematical terms it would be pythagoras:

squareRootOf((difference in latitude * difference in latitude) + 
             (difference in longitude * difference in longitude))

Really haven't a clue how to do this. Any help appreciated greatly

In Sql Server 2008 there is a spatial index functionality which is built to help in these kind of scenarios, however I don't think it is supported by EF. — Anders Abel, Aug 08 '11 at 17:17

score 4 · Accepted Answer · answered Aug 08 '11 at 18:30

There is no need for a square root at all; ordering by the square of the distance is the same as ordering by the distance:

.OrderBy(x => (x.Latitude - target.Latitude)*(x.Latitude - target.Latitude)
              + (x.Longitude - target.Longitude)*(x.Longitude - target.Longitude))

This trick is often used in collision detection (such as for video games) to avoid having to calculate many square roots.

score 0 · Answer 2 · edited May 23 '17 at 10:34

0

How about implementing your own IComparer that calculates that pythagorean square root? Then the OrderBy will automatically compare off that.
See this post for an example.

edited May 23 '17 at 10:34

Community

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answered Aug 08 '11 at 17:22

dizzwave

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Doing Mathematical calulations in Order by with Linq

2 Answers2