How to Import Mexican DRG maps

using Oziexplorer's registered version

 

 

Mexican digital topo maps are created as DRG (Digital Raster Graphic). This type of files can be easily imported by Oziexplorer.

When you get a Mexican digital map you will receive a CD or a Folder with the Map Number in accordance to INEGI's identification system, for example E14A28. Into this folder you will see several files, all of them starting with the same Map Number but different extensions. Those are (the XXXXX represents the Map Number):

XXXXX.gif

Raster image file in GIF format. Not recognized by Oziexplorer.

XXXXX.gfw

 "World Map" file  with georreferencing information for the GIF image.

XXXXX.tif

Raster image file in TIFF format. This is the one we will use to import the map.

XXXXX.tfw

 "World Map" file  with georreferencing information for the TIF image. We will also use this file.

XXXXX.txt

Text file with information regarding the digitalization process. It includes the map datum and projection which we will need later on the process.

 The Import Process

Create a folder in the computer hard disk with the number of the map. Copy in it the  TIFF, TFW and  TXT files. There is no case in copying the GIF and GFW as  Oziexplorer does not recognize them.

Open the text file and look for the Map Projection and Datum. The following table shows the contents of this file and has the Projection and Datum highlighted in yellow.

 IMAGEN DIGITAL CARTA TOPOGRÁFICA ESCALA 1:50000.
E14A56

DESCRIPCIÓN.

La carta imagen digital consiste en una imagen que tiene el mismo
contenido que la carta topográfica escala 1:50000 impresa.

Además del cuerpo del mapa, se incluye la leyenda marginal para facilitar su
interpretación.

La edición de la Carta y esta imagen se prepararon mediante procesos
digitales a partir de datos vectoriales.

Se incluyeron archivos de imagen en formatos .tif y .gif, se agregan datos
de georreferencia, con la que esta imagen puede combinarse con otra información
geográfica, utilizando herramientas adecuadas.

PROYECCIÓN, DATUM.

Proyección Universal Transversa de Mercator
Cuadrícula UTM a cada 1000 m

Datum: ITRF92
Elipsoide: GRS80

Coordenadas de la esquina superior izquierda de la imagen (noroeste):
x:356552.528827822
y:2104501.25922222

Dimensiones del pixel:
x:10.3565369332121
y:10.3559609631792

ARCHIVOS DE IMAGEN
e14a56.gif
e14a56.tif

FORMATO
GIF y TIF

INFORMACIÓN DE GEORREFERECIA: (ARCHIVO "WORLD")
e14a56.gfw
e14a56.tfw


FECHA DE PREPARACIÓN DE IMAGEN:
Marzo del 2002
 

 

Load Oziexplorer and click on  "File/Import Map/Single DRG", as shown below:

 

 

 

The dialog shown next indicates to look for the image file.

 

 

 Browse to the folder previously created  and select the TIFF file.

 

 

The next dialog will show. Give a name to the map and the path to save it.

 

 

I recommend you use the same folder where the INEGI files are stored.

 

 

Now the next dialog will show asking for the map's geographic reference information. Remember that INEGI maps may be in NAD27 or  ITRF92 Datums. If it is in ITRF92 you should use WGS84 as  Oziexplorer does not support  ITRF92.  The projection and zone will also have to be introduced.

 

 

If all is correct, the next dialog will show.

 

 

 

The map is displayed and you can now work on it.

 

 

 

 

For any question about this process, do not hesitate to contact us. We also strongly recommend that you read Oziexplorer´s Help-

 

Alberto Nájera

August, 2003

 

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