[Proj] lat/long format question

Roger Oberholtzer roger at opq.se
Fri Oct 30 14:34:32 EST 2009

On Fri, 2009-10-30 at 17:22 +0100, OvV_HN wrote:
> ----- Original Message ----- 
> From: "Roger Oberholtzer" <roger at opq.se>
> To: "PROJ.4 and general Projections Discussions" <proj at lists.maptools.org>
> Sent: Friday, October 30, 2009 1:09 PM
> Subject: Re: [Proj] lat/long format question
> ....
> > My data is a third representation:
> >
> > 3.5 in dd.ddd is 330.0 in ddmm.mmmm
> > 43.5 in dd.ddd is 4330.0 in ddmm.mmmm
> >
> > The ddmm.mmmm format is how Trimble receivers provide lat/long values in
> > NMEA GGA records, while the dd.dddd format is what Garmin receivers
> > provide in their NMEA GGA records.
> Ah! I didn't realise such a format was among the actually used ones.
> Shouldn't the EPSG database list this format in the section 
> epsg_unitofmeasure?

I come across dd.dd ddmm.mm and ddmmss.ss

Frank reminded me that it is radians that I am passing. Of course this
is the case. Too much to keep track of. And, it is Friday (and a partial
holiday in Sweden).

So the answer to my question is that I must arrange dealing with this
outside proj4. Which I am fully in agreement with.

> Or is it a proprietary format, only used by Trimble?

I cannot say. I would be curious to know what is the most common. I
think the NMEA standard states ddmm.mm. So I think it is the Garmin that
is non-standard. Even if it is very common. We have always used Trimble.
And Applanix. I will have to check what we are doing with Applanix data.
The Garmin experiment is for those of our users not requiring accuracy
beyond some meters.

> Anyhow, wouldn't it be more productive if the PROJ command line had a flag, 
> denoting the format of the DMS input and output?

For data arriving at the library via that route, perhaps. My use is via
the C API in an application that tracks locations in real time. We use
the library direct, providing radians.

You can't just ask customers what they want and then try
to give that to them. By the time you get it built, they'll
want something new.  -- Steve Jobs

Roger Oberholtzer

Ramböll RST/OPQ

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