Convert "geometry" into "geography"

I'm on a test project to learn about geolocation tools. But being a neophyte, a few concepts in PostGIS escape me. Here's my problem: The SRID used was 4326. I have three fields: The field "geocenter" in which I store the center of my circles, the field "georadius" in which I store circle radii and the field "geocircle" in which are stored circles that are really just polygons . By using the ST_Buffer, I notice that some of the tops of my polygons (circles) exceed the range [-180 -90 180 90]. My concern is to calculate the distance from a point outside the circle from the circle. ST_Distance using these polygons of geometry types, I find that the calculated distance is wrong. I thought then used a CAST but I am having this error: Coordinate values ​​are out of range [-180 -90 180 90] for GEOGRAPHY type. Please, it is there a way to convert these "geometry开发者_高级运维" data in "geography" data although the points are outside the range [-180 -90 180 90]? thank you

I found: Well, I knew there was an overload of the ST_Buffer for geographic data types! It was therefore necessary to use ST_Buffer (geography, double) instead of ST_Buffer (geometry, double)