Re: [Texascavers] Re: gps datums and projections

Mon, 9 Jul 2007 05:40:49 -0700 (PDT)

NADCON (from the US Geodetic Survey) is such a conversion package and is (still) free for download..

 

T.


-----Original Message-----
From: [email protected]
Sent: Jul 6, 2007 1:27 PM
To: [email protected]
Cc: [email protected], 'Nico Escamilla' , 'texas cavers'
Subject: [Texascavers] Re: gps datums and projections

Thanks Andy,

 

That is basically what I was referring to.  When you pick up your handy garmin or whatever brand unit, it is defaulted to WGS 84.  The DOD (which is the real proponent for maps that are generated) and the FCC and the FAA and the USGS all publish in WGS-84 today.  When you pick up a modern MGRS/UTM map from the military it is also now in WGS-84. USGS maps atre in WGS-84.  Old maps still have the Datum referenced on them. 

You can easily convert WGS-84 to NAD-1927.  They key is to realize that World Geological Survey 1984 (WGS-84) is more up to date than the 1927 model where we were not as accurate. It just makes sense to move on. 

I can actually tell you stories about being given MGRS locations in WGS-84 thinking they were in NAD-27, programming a navigation system that was in NAD-27 and being given maps in WGS-84 and not knowing the mistake until airborne.  That is a bit harder to work out as the error changes and the internet is not available in flight.

There are programs everywhere that will help you convert datums and as long as you know the source, you can convert.  Some of the main references to position such as radio towers must be located using WGS-84 so why not ride that horse ?

 

 



----- Original Message -----
From: Andy Grubbs <[email protected]>
Date: Friday, July 6, 2007 10:52 am
Subject: Re: gps datums and projections
To: [email protected]
Cc: [email protected], 'Nico Escamilla' <[email protected]>, 'texas cavers' <[email protected]>

> The native datum for gps units is WGS 84. The TSS ought to be very
> happy to get data in that. I understand the reasons why TSS uses
> NAD 27
> and they are not the only organization that does this. The topo maps
> that everything is based on go back to NAD 27 and organizations with
> large legacy data sets try to keep everything the in the same
> datum/projection. however we see more and more of those folks
> modernizing these days.
>
> Not all cavers know how to get into the settings of their gps
> units and
> change from WGS to NAD and they may have reasons why they dont
> want to.
> also the NAD 27 datum could be for UTM, Lat/long or even State Plane
> projections. once again different organizations use different
> projections. no mention of the preferred projection has been made.
>
> The TSS can easily convert whatever they are given into what it is
> thatthey use since they have GIS programs and people who are
> proficient in
> their use. TSS has a history of accepting cave data however they can
> get it. cave location maps drawn on napkins comes to mind. The
> easiestformat for the average caver is WGS 84 Lat/Long DD. I think
> that is also
> what the gis type programs average cavers have access to use. like
> google earth ect ( I dont use these so I am not positive about
> this ) In
> the long run the vast majority of data/internet acessable maps are
> goingto be in this datum/projection
>
> [email protected] wrote:
>
> >
> >
> > NAD 27??
> >
> > Why not just have the user state what they used? The conversion is
> > very simple.
> >
> > ----- Original Message -----
> > From: Ron Ralph <[email protected]>
> > List-Post: [email protected] Date: Friday, July 6, 2007 7:50 am
> > Subject: RE: [Texascavers] comanche cave
> > To: 'Nico Escamilla' <[email protected]>, 'texas cavers'
> > <[email protected]>
> >
> > > Nico, Hazel and cavers,
> > >
> > >
> > >
> > > There is a Comanche Caves Ranch in the Texas Speleological Survey
> > > database(KER014) but there is absolutely nothing known about the
> > > cave or the ranch.
> > > If anyone should visit, please provide a trip report along with
> > > digitalphotos and a GPS location using NAD 27. Texas cavers will
> > > be eternally
> > > grateful.
> > >
> > >
> > >
> > > Ron Ralph
> > >
> > > President, TSS
> > >
> > >
> > >
> > > _____
> > >
> > > From: Nico Escamilla [mailto:[email protected]]
> > > Sent: Thursday, July 05, 2007 5:35 PM
> > > To: texas cavers
> > > Subject: [Texascavers] comanche cave
> > >
> > >
> > >
> > > Hazel Barton's message on the NSS Cavechat
> > >
> > > All,
> > >
> > > I have a good friend who needs some information on Comanche Cave,
> > > on the
> > > Comanche Ranch in Hunt Texas. If anyone knows anything about these
> > > caves,could you please contact me directly.
> > >
> > > Many thanks,
> > >
> > > Hazel
> > >
> > >
> > > Can y'all help with this?
> > >
> > > Nico
> > >
> > > typing from Caving Paradise/Cave Capital of the World
> > >
> > >
>
>
> 


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