[Proj] where is the default origin ?

[Randy]

Hi Glynn,
Thanks for your timely response!
> > I'd like to know where the default origin is when I do Mercator
> > projection like this:
> > from "+proj=latlong+ellps=WGS84+datum=WGS84"
> > to   "+proj=merc+lat_ts=30+ellps=WGS84+datum=WGS84+unit=meter"
> > 
> > I just know the default origin is the point of intersection with
> > greenwich and equatorial when I use the default latitude of true
> > scale,but if now the latitude of true scale is decided by "lat_ts",where
> > is the default origin?
>  
> It's still at the intersection of the prime meridian and the equator.
Best regards,
Randy