BuildCircleMbr radius definition

[Jim]

I have a couple of questions for function  BuildCircleMbr

1. For SRID 4326, what is the unit-of-measure for "radius"?

2. Given the answer for question 1, how does one convert "US Statute Miles" to that unit-of-measure?

Regards,
Jim

[Brad Hards]

On Tue, 28 Jul 2015 06:33:33 PM Jim wrote:
> I have a couple of questions for function BuildCircleMbr
>
> 1. For SRID 4326, what is the unit-of-measure for "radius"?

Its in degrees - defined by the SRS.

> 2. Given the answer for question 1, how does one convert "US Statute Miles"
> to that unit-of-measure?

Short version: You probably don't want to do that.

The longer version is that for pretty much anywhere in the US, miles are not
going to convert cleanly to degrees (at least, it won't be a circle). So you
probably want to reproject (i.e. ST_Transform) to some kind of SRS that does
match (e.g. a state plane, or UTM, or whatever makes sense for your data area
and functional need). There is no sane way to do this for "anywhere". You
might be able to do "anywhere in the US", but it depends on what you're trying
to do, the data that you need to reproject (e.g. are they all points, or do
you have lines and polygons), and how much accuracy you need.

Brad