Ghansham,
my understanding is that usually Mercator has the center latitude (or
standard parallel) =0 , which corresponds to a scale factor of 1. If
you want true scale (=1) at a given latitude, then you use either
variant using standard parallel(in your case CenterLatitude) or a
scale factor computed from that latitude using the equation in
http://www.remotesensing.org/geotiff/proj_list/mercator_2sp.html or
Snyder.
Any way, if you have CenterLongitude and CenterLatitude, then use the
standard_parallel version in CF.
Etienne
On Thu, Feb 2, 2012 at 5:28 AM, ghansham sangar
<ghanshamsangar at gmail.com> wrote:
> Well thanks a lot for the help. I visited that link. Actually I understood
> your point of view.
> I was more confused with the parameter naming convention in case of
> Mercator_2SP:
> We here in India generally used USGS map projection parameter naming
> convention.
> See through this:
> http://isis.astrogeology.usgs.gov/IsisWorkshop/index.php/Learning_About_Map_Projections#Projection_and_Parameters
>
> For mercator (2SP case), it says the projection parameters are
> CenterLongitude and CenterLatitude.
>
> which in your convention is (
> http://www.remotesensing.org/geotiff/proj_list/mercator_2sp.html?):
>
> 1. Latitude of first standard parallel
> 2. Longitude of natural origin
> So that was a big confusing
>
> Anyways thanks a lot.
> Just point out if I am wrong in understanding.
>
>
> regards
> Ghansham
>
> On Wed, Feb 1, 2012 at 6:42 PM, Etienne Tourigny <etourigny.dev at gmail.com>
> wrote:
>>
>> Ghansham,
>>
>> It is usually one, but "more common formulation for Mercator is to
>> drop the +k_0, and instead to provide a latitude of true scale using
>> the +lat_ts parameter, which is the latitude at which the scale is 1."
>> The latter would be using the standard_parallel version instead.
>>
>> See http://www.remotesensing.org/geotiff/proj_list/mercator_1sp.html
>>
>> hope this helps
>> Etienne
>>
>> On Wed, Feb 1, 2012 at 10:38 AM, ghansham sangar
>> <ghanshamsangar at gmail.com> wrote:
>> > R/Sir
>> >
>> > Can somebody tell me what is the value of
>> > 'scale_factor_at_projection_origin' for mercator projection?
>> > If somebody can provide some example it will be really useful.
>> >
>> > looking forward for an early response.
>> >
>> > regards
>> > Ghansham
>> >
>> > _______________________________________________
>> > CF-metadata mailing list
>> > CF-metadata at cgd.ucar.edu
>> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>> >
>
>
Received on Thu Feb 02 2012 - 07:21:48 GMT
