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Author: Subject: Topo maps
bacquito
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[*] posted on 7-29-2012 at 11:35 AM
Topo maps

I am an amateur at using topo maps.
I recently obtained a topo map from INEGI while in TJ.
The maps are 1:50000 maps, 5' per graticule.
I follow a precedure described in a site from Oregon: "determine latitude and longitude"
I'm off by about a mile in Lat. but right on in Longitude.
The map of interest is in the Valle Guadalupe area near Cetto.
Any help/suggestions are appreciated.



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bajaguy
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[*] posted on 7-29-2012 at 01:19 PM


May be helpful:

http://www.globalsecurity.org/military/library/policy/army/f...



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bacquito
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[*] posted on 7-29-2012 at 01:47 PM


Quote:
Originally posted by bajaguy
May be helpful:

http://www.globalsecurity.org/military/library/policy/army/f...


Thanks, Roger



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[*] posted on 7-29-2012 at 01:51 PM


Make sure you match the map datum if using a GPS. Mexican topos are NAD27 Mexico and GPS units are set at WGS84.



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[*] posted on 7-29-2012 at 01:56 PM


Quote:
Originally posted by bacquito
Quote:
Originally posted by bajaguy
May be helpful:

http://www.globalsecurity.org/military/library/policy/army/f...


Thanks, Roger





Ahhhhhh, I'm not Roger, but you are welcome!!!!!



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bacquito
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[*] posted on 7-29-2012 at 02:42 PM


Quote:
Originally posted by David K
Make sure you match the map datum if using a GPS. Mexican topos are NAD27 Mexico and GPS units are set at WGS84.


Thanks, I used a procedure described in Google "determine Lat. and Long" from an Oregon. It seems streight forward but the results were disappointing.
I, as a test, used the village San Antonio Necua below LA Cetto to determing Lat. and Long. My results were different than indicated on Google Earth.
Confused and amused!



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[*] posted on 7-29-2012 at 04:57 PM
GPS Corrections

Echoing David, be sure your Datum is set correctly, to agree with the map/chart.
Check that both Google Earth and your GPS are set for True or Magnetic. To get to magnetic from true the variation is probably about 13 degrees.
When I have marked locations from Google Earth they have been very close to GPS, when at the location.
Good luck.
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bacquito
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[*] posted on 7-29-2012 at 07:39 PM


Quote:
Originally posted by skippermike
Echoing David, be sure your Datum is set correctly, to agree with the map/chart.
Check that both Google Earth and your GPS are set for True or Magnetic. To get to magnetic from true the variation is probably about 13 degrees.
When I have marked locations from Google Earth they have been very close to GPS, when at the location.
Good luck.


Thanks-Yes when I use Googe Earth and my GPS to locate an object I get good results



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[*] posted on 7-30-2012 at 09:50 AM


Google Earth is also at Map Datum 'WGS84'... but a Mexican Topo (incl. the Baja Almanac) is drawn at Map Datum 'NAD27Mexico' Usually the two are very near each other, but if you are trying to be exact it may be an important setting change to make.



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[*] posted on 7-30-2012 at 09:52 AM


Quote:
Originally posted by bacquito
Quote:
Originally posted by David K
Make sure you match the map datum if using a GPS. Mexican topos are NAD27 Mexico and GPS units are set at WGS84.


Thanks, I used a procedure described in Google "determine Lat. and Long" from an Oregon. It seems streight forward but the results were disappointing.
I, as a test, used the village San Antonio Necua below LA Cetto to determing Lat. and Long. My results were different than indicated on Google Earth.
Confused and amused!


Being both confused and amused is a frequent condition in Baja California!:lol::light:



"So Much Baja, So Little Time..."

See the NEW www.VivaBaja.com for maps, travel articles, links, trip photos, and more!
Baja Missions and History On Facebook: https://www.facebook.com/groups/bajamissions/
Camping, off-roading, Viva Baja discussion: https://www.facebook.com/groups/vivabaja
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bacquito
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[*] posted on 8-3-2012 at 12:17 PM


Thanks to all, I finally figured I was assuming the minutes between graticules was 5' but instead it was 2.5', so I was using the wrong factor.
Everything turned out fine.
Hope all are enjoying a good day. Great weather in Ensenada today.



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