manually calibrate a Mexican topographic map in Oziexplorer you need to
provide the coordinates of at least 2 known points (I recommend to use 3 to
4 points to increase accuracy). Once you enter this information Oziexplorer
will generate the Map file that will allow you to work with your GPS. You
need to choose the coordinate system that will be used to obtain the points
coordinate scales for both Lat/Lon and UTM are printed on the borders of
the map. The map Datum is located in the information section of the map as
shown below in the red rectangle. Mexican maps are made in 2 datums: ITRF92
(which is the same as WGS84)
or NAD27 CONUS. It is identified in Spanish as
“Datum Horizontal”. See below .
Mexican topo maps in the 1:50,000 and 1:250,000 scales are made in UTM
projection as shown in the blue box.
If you decide to use UTM, besides the datum
you will need the UTM zone in which the map lies. You can find it in a table
like the one shown below in green:
the original paper map identify 3 to 4 points that are within the scanned
area. Look for points that have whole number coordinates in the system you
decided to use and close to the corners of the scanned area to help minimize
errors and to make the process easier. Make sure to write the complete
coordinate number for each point and write them down.
Start Oziexplorer and choose File/Load and
Calibrate Map image.
Browse to the directory where the image you want to calibrate
is stored and open it.
The map image will show on the left side of the screen
and the calibration window on the right side. On
the “Setup” tab enter the required information: the datum from step 2 above
( If the map datum is ITRF92 on the map use WGS84 in Oziexplorer), and
select “(UTM) Universal Transverse Mercator”, on the map “Projection” drop
Then select the “Point 1” tab and the cursor
will take a cross shape. Locate the cursor over the first point of which you
know the coordinates (step 4 above) and click. Enter the coordinates in the
corresponding fields of the calibration window. If you are using UTM you
will need to enter the zone, easting and northing. If you are using Lat/Long
you will be asked to enter these two values. DO NOT PRESS THE SAVE BUTTON.
select the “Point 2” tab and repeat the process mentioned above for the
second point. Repeat for all the points identified
in step 4 above. Once all the points have been entered press SAVE and name
new map is ready for use.
you need more information on this process check Oziexplorer’s help.