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Importing DRG Maps
For Registered or Retail copies only.
While it is simplier to be able to import the DRG maps, it is possible, for those which
cannot be imported, to calibrate the maps by hand using 3 Lat/Long points, 3 corners of
the map are quite adequate for an accurate calibration.
Introduction
This option is mainly aimed at importing the USGS DRG raster maps provided by the USA
government but can also be used to import any of the supported map image types
(TIF,BMP,PNG,JPG) which have at least a .TFW file.
DRG stands for Digital Resource Graphic but are
really images of maps in a digital image format.
A .TFW file is a simple text file which contains very basic
calibration (georeferencing) information.
A Geotiff image file has the calibration (georeferencing) data
embedded within the image file.
OziExplorer has various levels of importing these maps and trys to select the method
which has the most information to give the best calibration and other parameters.
The georeference information is obtained in this order of priority:
If the file is a geotiff and the information is in the correct format or,
from the TFW file if it is available or,
from the FGD file if it is available
If the FGD file is available then additional information is obtained
from it :
If the positions of the corner markers can be obtained then 3 of the corners are used
as calibration points. There have been the some instances where the corners of the map
stored in the FGD file are in error, this produces an incorrect calibration.
Maps from other sources may have a .XML or .MET file
and these serve a similar purpose.
If there is no DRG (or similar) file and the image is not Geotiff then the .TFW file is
used. This file contains very basic calibration information and is missing some necessay
parameters, this process is described fully below, see Importing DRG's
with only a .tfw File .
If none of the above are available then the map image cannot be imported and must be
calibrated manually.
Geotiff
OziExplorer can extract the georeference information from Geotiff files but it only
knows how to decode the information if it is from a known source. At this stage only the
georeference information in the USA USGS DRG Geotiffs can be decoded.
The ability to decode other sources of georeference information in Geotiff files will
be added on an as need basis where it is possible to do so.
Importing a Single DRG Map
Select the Import Map/Single DRG Map Option on the File Menu.
Step 1 - Find the TIF file of the map you want to import.
You need to know the name of the image file of the map you want to import. You will
have to find out this name from the information supplied with the CD, I would assume.
Press the OK button and the software will allow you to navigate through your Disk
Drives and Directories until you locate the file. If the CD is from the USGS then the file
would normally be located in the DATA. When you have located the file, select it by double
clicking on the name or click on the name and press the Open button.
A METADATA (FGD or other) file may also be available for the image. This is usually
located in the METADATA directory of the CD. If you copy the image file to your hard drive
the metadata (FGD) file must also be copied and placed in the same directory as the image
file.
Step 2 - Specify the Name and Path of the OziExplorer Map file you want to
create.
The Map file name will be the same name as the image file but with a .MAP extension.
The name of the file can be changed but do not change the extension. Save the file.
Step 3 - The newly created Map will now be opened.
From now on you open the Map by selecting the MAP file using the Load Map from File
option. The original image must always be available when opening the map.
The map calibration used can be viewed using the normal Check Calibration of
Loaded Map menu option.
Importing a DRG CD
This option allows you to import all DRG maps from a CD but can also Import DRG maps
which have been copied to a Hard Disk. If you do copy the image files to the hard disk you
must also copy the fgd files from the metadata directory, place these in the same
directory as the tif files.
Select the Import Map/All DRG Maps on CD Option on the File Menu.
The Import DRG Maps dialog will appear.
Image File Path - The path where the Image files are located. Press
the button at the right hand end of the Image File Path field (or enter the Image
File Path directly into the field). Select the path (directory) by browsing the disks.
Map File Path - The Path where the created map files will be placed.
Press the button at the right hand end of the Map File Path field (or enter the Map
File Path directly into the field). Select the path (directory) by browsing the disks.
Use Geotiff if available - If checked and the map images are in
Geotiff format and the format is known then the georeference information will be extracted
from the image file.
Press the Import button, the maps will be imported.
The new map files are created in the Map File Path you have specified in the
configuration.
At the end of the process the number of maps successfully imported (and not imported if
any) will be displayed.
The maps are now ready to use, simply open the map you want to view using the
OziExplorer Load Map from File menu option.
Importing DRG's from U.S. Tennessee Valley Authority (TVA)
These DRG's have a metadata file (.met) in a slightly different format to the usual fgd
file which comes with the DRG's from the USGS.
When importing into OziExplorer these maps can be treated the same as any other DRG.
OziExplorer will check the CD to find the type of maps available and adjust its import
method accordingly.
On the CD it is assumed the tif and tfw files are in the DATA directory and the met
file is in the METADATA directory.
If copying the files to a hard disk put all the files in the same directory.
Only maps in Universal Transverse Mercator projection can be imported, maps in the
State Plane Coordinate System cannot be imported.
Importing DRG's from Pennsylvania State
University
These are available from this web site http://www.maproom.psu.edu/drg1/
To obtain the DRG's and import them into OziExplorer follow these steps. It is assumed you
are on the web page of the university.
1. Locate the DRG you want from the map.
2. Download the DRG from the web site, you will get the tif image file and the tfw file
within the zip file.
3. Download the metadata file (unformatted), this is an xml file. It is
preferred to use the "Save as File" (or similar wording) using the right click
button in your web browser.
4. Unzip the tif and tfw file to a directory on the hard disk.
5. Copy the xml file into the same directory.
6. The xml file will have a different name to the tif file, you must rename the xml
file to the same name as the tif file but with an xml extension.
example: you should have 3 files named something like this o41234a1.tif
o41234a1.tfw o41234a1.xml
Note : the xml file does not contain all the information to import a map,
the tfw file is also needed. Neither of these files contains the datum so NAD27
CONUS has been assumed for all maps.
Importing DRG's from Wyoming
These are available from this web site http://wgiac.state.wy.us/wsdc/usgs/drg/AboutDRG.html
To obtain the DRG's and import them into OziExplorer follow these steps. It is assumed
you are on the web page.
1. Locate the page to download the DRG.
2. Download the DRG from the web site, you will get the tif image file and the tfw file
within the zip file. There is also a tab file but this is not needed.
3. On the page to download the DRG is also a link to the "Full Metadata", the
link is very prominate in a large bold font. Select the metadata page, and when loaded
save the page as a txt file. Use the browser "Save As" option and select
"Text file" as the file type.
4. The metadata file will be saved with a .txt extension. Rename the file to an xml
file - change the .txt extension to a .xml extension.
5. Unzip the tif and tfw file to a directory on the hard disk.
6. Copy the xml file into the same directory.
7. The files should all have the same name but with different extensions.
example: you should have 3 files named something like this o41234a1.tif
o41234a1.tfw o41234a1.xml
Note : the xml file does not contain all the information to import a map,
the tfw file is also needed.
You can now use the normal OziExplorer Import Map options to import the maps,
OziExplorer will work out the various file types available and use the appropriate ones.
Importing DRG's with only a .tfw File
This also applies to JPG files which have a .jgw file, the jgw file is the same as a
tfw file, OziExplorer will now use this file automatically if it exists.
While not preferred, it is possible to import DRG maps which only have the .tif (or
other image format) and a .tfw file. There are a lot of parameters missing
such as datum, UTM zone number, scale, map bounding coordinates + others. Most of these
can be ignored and set manually after the map is imported.
A dialog will be opened which requests some of this information.
Map Datum - specify the map datum to be used.
Map UTM Zone - specify the zone, 2 digits only. For UTM projection maps the UTM
zone number must be known to import the map so you must know this in advance. On the USA
DRG maps the zone number is usually provided on the lower left hand corner of the map
image, the datum is also provided there. You will need to open the map image in a paint
program such as Paint Shop Pro www.jasc.com to view the
image.
If you are importing a USA USGS DRG map with just a tfw file and the map image name is
in the standard USGS format (example O43107C4.TIF) then OziExplorer will work out the
correct UTM Zone number to use from the file name and put it in the Zone field of the DRG
Import Options dialog as the default.
Hemisphere - Select the correct Hemisphere (North or South of the
equator).
Always Ask - if checked this dialog will be shown for each map imported, if
unchecked the parameters entered into the dialog will be assumed to apply to all maps.
Drg Projection - only 4 projections are supported, UTM, Albers Equal Area,
Lat/Long and NZ grid. If specifying Albers you must also enter the other parameters,
latitude 1 & 2 , central meridian and false nothing etc. The Albers projection may be
required to import maps from the Teale Data Centra.
Not all tfw files have the data values exactly as OziExplorer expects, so not all maps
can be imported correctly with just the tfw file.
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