BillB - 4-10-2005 at 10:09 AM
Now that everyone has had a few days to enjoy the new satellite photography of Baja made available on Google: (http://maps.google.com) how many of you have figured out how to locate the GPS coordinates directly from the Satellite photographs? Lets say you
are searching the Satellite images of an area that you plan on exploring, and find something that looks so interesting that you want to check out on
your next trip, like maybe a dirt road you never knew was there. How cool would it be to be able to quickly get the GPS coordinates of the place you
wanted to check out? The fact is, it is easier than you can imagine? you just need to know a couple of tricks.
Here is what you do to get GPS coordinates.... First, find a place you want to locate. Here for example is the URL link to the turn off from Hwy 1 to
Bahia Los Angeles:
http://maps.google.com/maps?ll=29.045276641845703,-114.15241...
Now look up that the url... does it look familiar? The GPS coordinates are staring you right in the face! (29.045276641845703,-114.15241241455078)
These first two sets of numbers are the latitude and longitude of the center of the photograph, but they are in a slightly different format then you
are used to seeing. They not in Degrees and Minutes (D.MM), which is the convention most of us use in our GPS units. Instead, they are found in the
format of Degrees and Tenths of a Degree (D.DD). While a bit confusing at first, there is no need to worry, as most if not all GPS units are capable
of displaying your coordinates in the D.DD format. The really good news is that when you switch to the D.DD format on your GPS, it does not mess up
the waypoints you have already saved, it just converts them back and forth for you. I know this to be true for Garmin units, but it is probably also
true for other manufacturers.
You always have the option of going a little math to convert back and forth from D.MM to D.DD. You must simply remember that there are 60 minutes to
each degree, so you simply multiple or divide by 60 to do the conversion. One helpful tip is to remember that if someplace has LAT/LON coordinates of
something like 38 degrees 30 minutes, it would be same as 30.5 degrees (30 minutes is 50% of a degree).
Lets convert the example above from D.DD to D.MM to see if it works.
The URL tells us that the center of the photograph (where I double clicked on the middle of the junction) tells us that the LAT/LON is
29.045276641845703,-114.15241241455078. First, lets round it off to 29.045, -114.152.
So to convert the Latitude, we take the ?.045? (tenths of a degree) and multiply it by 60 to get 2.7 (minutes). So the converted Latitude is 29
Degrees, 02.7 Minutes.
Similarly, converting the Longitude: .152*60 = 9.12 giving us ?114 Degrees, 09.12 Minutes.
So now we have the ?normalized? GPS coordinates of the Highway 1 and LA Bay Junction to be 29 degrees 02.7 minutes, and ?114 Degrees, 09.12 minutes.
How accurate is this?
David K was kind enough to post a comprehensive list of Baja GPS coordinates a while back, and here is what he showed for the Highway 1 and LA Bay
Junction: 29?02.75'/ 114?09.13'
SPOT ON! How cool is that?
IMPORTANT:
Before you ?try this at home?, there is one more important trick you need to know? Go back to the URL I gave you, and try double clicking around in
different places on the photograph and watch the URL... While each time you double click the map does re-center on that spot, the URL does not
change,,, so how you ask, could this possibly work? Well? here is the secret.... double click on the point you want to center it... then click on the
place in the window that says "link to this page" and watch your URL... Bingo...it will update and be spot on for GPS coordinates!
Enjoy!
Bill B
Dallas
Bruce R Leech - 4-10-2005 at 05:05 PM
welcome BillB nice to have a new Bajanomad.
that is pretty neat info I'm going to use it and I am sure other Nomads will as well.
bajalou - 4-10-2005 at 05:11 PM
Good Work Bill B. I'll be using that a lot I believe.
Mexray - 4-10-2005 at 08:25 PM
Here's a waypoint converter that lets you convert from/to any format you want....don't forget to check the 'N' and 'W' buttons on the left or you will
get an error...
http://www.oasisphoto.com/navigation/convert_form.php
bajalou - 4-10-2005 at 09:43 PM
Thanks Mexray - of course I didn't check the "N" or "W" befor trying to get it to convert and got the predicted "error"
Thank BillB
David K - 4-11-2005 at 07:28 AM
Thanks Bill,
Were you able to determin what map datum the site uses... obviously it is very close to my waypoints which are at map datum NAD27 Mexico...?
Bill loves exploring Baja and has a unique Rokon 2WD motor scooter for doing so... Only work and the distance from Texas keeps him from being there
constantly!
Max and Corky joined him last year trying to get from El Huerfanito (Nacho's) to El Marmol, in Arroyo El Volcan... a dry waterfall rock face halted
easy progress west.
Here is Bill two years ago at Viva Baja 4, when I met him:
My Baja GPS waypoints are found in my web site, and notebook pages, listed below...
Wow, that's cool!
neilmac - 4-11-2005 at 10:06 AM
... is there a way to enter the lat/lon, and have it show the map?
Neil
wornout - 4-11-2005 at 04:00 PM
To BillB: Thanks BillB for the GREAT info
To neilmac: Not yet but I am sure it will be coming. (actually you could do a click and find thing, sort of the reverse of what BillB mentioned in
the beginning of this thread, but it would take a long, long, long time to zero in).
BillB - 4-11-2005 at 07:38 PM
It's really not all that difficult to work backwards to find a particular spot that you have the coordinates for. The first thing you have to do is
make sure you have the coordinates in D.DD format (see above), then start working your way closer by double clicking on a spot, and then clicking on
"Link to this page" to get an updated URL with new GPS coordinates. It won't take you long to figure out that as you move up (north) the latitude
numbers increase, and as you move left (west), the longitude numbers grow larger (technically they decrease as they are a negative number, but you
will get it).
After a few minutes you will get the hang of how much things increase or decrease for a given amount of movement. Obviously that changes based upon
the level you are zoomed in.
David: I think the datum is the standard U.S. (WGS-84/NAD83) as there are no breaks between Southerns CA, and BAJA, and the obvious focus of the
database is the US. Not much difference between the two anyway. Probably less than 100 meters.
David K - 4-11-2005 at 07:42 PM
Thanks Bill... that's great!
So, when are WE going into Sal Si Puedes, from the Dry Lake?
