>if I have
>X�s and Y�s coordinates that i obtain with GPS and it have the datum WGS84
>how I can change or how I can traslate that coordinates whit that datum to
>another in Venezuela??? in MAPINFO???
Ah, GPS is our friend (most of the time) ...
We've found GPS works great when attached to a laptop running MapInfo and
(included in the USA versions) GeoTracker, and building tables in real
time. It's kind of a hassle to drag around the equipment for small jobs,
but it's the most effective way to make sure you've got the data you need,
since you can quality check it, on screen, as you work. And when you're
finished you've got the table already built.
Bringing waypoint data from the GPS into MapInfo is more problematic. The
steps include getting the data from the GPS into a PC, transferring the
data from the comm program into a spreadsheet, massaging the data in the
spreadsheet into a form that MapInfo will take then making a table in
MapInfo. I'm always a bit self-concious about offering how we do things
since they may be less elegant than the ways some of the other posters on
this list might do it - there is real talent here! That being said, here's
how we do it:
We use a Magellan Nav DLX-10 which doesn't have it's own download program,
but instead uses any comm program and a serial port on the PC to transfer
the information. You have to have everything set exactly correct (in our
case 4800 baud, ASCII download, comm software set to autoreceive - all of
this always takes me about an hour to configure because I forget all the
little necessary steps between sessions). And you have to have everything
set exactly correct on the GPS - refer to the manual (I had to phone
Magellan because they left a critical step out of the instructions in the
DLX-10 manual). We use Win95 and Win98, and I remember having good luck
using HyperTerminal which is included with Win9x - or was I using the comm
package included with Win3.11? Anyway, I couldn't get HyperTerminal to
actually download the data, or even show it on the screen, so in
frustration I turned to my ever-useful MS Works95, which has a little
communications package built in. With that I was able to see on the screen
what the GPS downloaded (about 30 waypoints), which I copied and pasted
into the Works95 spreadsheet module. Whew!
The GPS default is Lat/Lon WGS84, so at least you know what your datum is,
eliminating that uncertainty. I always double-check to make sure that
hasn't been changed. It's probably possible to set your GPS so it will save
waypoints in digital degrees - do it if you can, to eliminate the next steps.
>From there I get rid of unnecessary columns (leaving just the X, Y and
waypoint number columns). The X and Y data download to the PC like
"4738.337" and "12240.866" which means you have to massage the coordinates
to get them into a form MapInfo will read accurately. My solution is to
copy the X coordinates to a new column, and the Y coordinates to a new
column, then for the new X column subtract 4700 and from the new Y column
subtract 12200. Then apply a simple formula where the numbers are divided
by 60 to give you a digital result, then add back in your degrees. At this
point you can can multiply the Y column by -1 (for North America). I then
have to EDIT/COPY my resulting columns, along with the waypoint number
column, into a new spreadsheet and "paste special" to get the "result"
numbers generated from the formulas (rather than an error since it
otherwise tries to copy the formula). I then FILE/SAVE AS that spreadsheet
in Lotus 123 format.
In MapInfo, choose FILE/OPEN TABLE and under "Files of Type" select Lotus
123 and go to the directory where you "saved as" your file in 123 format.
Bazingo! There they are! If they're not ... they probably appeared at
another location on the planet because you forgot a negative on the X or Y,
or something equally important but forgettable. I usually open a table of
the area where I'm expecting the points to appear so I can see immediately
how successful (or not) I've been - a table known to be well geo-referenced
(often for us orthophotography or NOAA nautical charts). Immediate
gratification.
All of the spreadsheet trauma could probably be automated into a script,
and there's probably a way of using MapBasic to do it as well. We do the
manual download thing so seldom that it just isn't worth the time for me to
hassle with figuring out how to automate it. Don't forget to write down
your steps so you can realize you forgot a step, and to have it for the
next time. Good luck!
Tom
* - * - * - * - *
Tom Curley
Suquamish Tribe GIS Program Manager
[EMAIL PROTECTED]
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