Question

I have a query that attempts to find things within a certain geolocation, but the results that it brings back are a little bit… strange.

I had previously posted this thread and the community helped me find a formula that I needed: Querying within longitude and latitude in MySQL but the query now gives really wacky results.

My data is surrounding the city of San Francisco which has the lat/lng 37.780182 , -122.517349

Query:

SELECT
    id,
    hike_title,
    lat,
    lng,
    ( 3959 * acos(  cos( radians(37) )
                  * cos( radians( lat ) )
                  * cos( radians( lng ) - radians(37.780182) )
                  + sin( radians(-122.517349) ) * sin( radians( lat ) )
                 )
    ) AS distance
FROM
    my_awesome_table
HAVING
    distance < 10000
ORDER BY
    distance
LIMIT
    0 , 50

So as you see – even if I make radius 10000 it still doesn’t find much, so I wonder if my query is off. Some of the results it brings back even have 0,0 for lat/lng which is my way to denote that there are no lat/lng for that record.

Here is how the formula is supposed to look like:

SELECT
    id,
    ( 3959 * acos(  cos( radians(37) ) 
                  * cos( radians( lat ) )
                  * cos( radians( lng ) - radians(-122) )
                  + sin( radians(37) ) * sin( radians( lat ) )
                 )
    ) AS distance
FROM
    markers
HAVING
    distance < 25
ORDER BY
    distance
LIMIT
    0 , 20;

Thank you and sorry for the painfully long question ! By the way, I am using MySQL.

---

Hmmm,

I just tried with the exact query you gave and it worked with 50% accuracy. Here is a sample of the data set:

    lat          lng    
| 37.223465 | -122.090363 |
| 39.320980 | -111.093735 |
| 38.031715 |  -84.495132 |
| 37.787144 | -122.493263 |
| 52.975361 |   -1.458620 |
| 40.848557 | -111.906883 |
| 40.572498 | -111.859718 |

So now the query returned all the items that were many miles away, but not the items which were under 100 miles away. Like this item ( 37.787144 , -122.493263 ) was never getting returned even though it is just about 50 miles from the originating point. Would you happen to know why?

Answer 1

I think you reversed the latitude (37.780182) and longitude (-122.517349) of your central point, try:

select
    id,
    hike_title,
    lat,
    lng,
    ( 3959 * acos(  cos( radians(37) )
                  * cos( radians( lat ) )
                  * cos( radians( lng ) - radians(-122.517349) )
                  + sin( radians(37.780182) ) * sin( radians( lat ) )
                 )
    ) AS distance
FROM
    my_awesome_table
HAVING
    distance < 10000
ORDER BY
    distance
LIMIT
    0 , 50