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UNB_TopoDens_2v02 Read Me File
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Overview:

UNB_TopoDensT_2v01 provides topographical density at three different grid 
spacings: 1 arc-degree, 5 arc-minutes, and 30 arc-seconds. The grid spacing is
denoted by the pre-fix to the file (1d, 5m, 30s) and the value is assigned to 
the cell center. There are also associated standard deviations at the same grid 
spacing, these files are denoted by "STD" in the name of the file. For more 
information on the creation of the UNB_TopoDens models, see associated article 
"Formulation and Validation of a Global Laterally Varying Topographical Density Model".

M.B. Sheng, Shaw, C., Vanicek, P., Kingdon, R.W., Santos, M., Foroughi, I.

Corresponding Author: m.sheng@unb.ca

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Version History:

1v00 - 	Initial raw product

1v01 - 	Refinements over Antarctica and various ice and water covered regions. 
     -	Cleaned up file structure for GMT products

2v00 - Published Models updated with density values from the PETLAB database

2v01 - Published models with minor changes to density values for ice/glaciers 
	 - New values for areas initially classified as "No-Data"

2v02 - Several interpolation problems identified in Antarctica were solved
	 - Updated standard deviation grids over Antarctica
		- Special thanks to Dr. Mehdi Goli for his help in identifying these errors 
		
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Extracting Lat/Long/Dens From Binary Format

UNB_TopoDens models are provided in *.grd file format which is the native binary
file structure utilized by the Generic Mapping Tools software (GMT). In order to 
transform these into *.txt files with a [latitude, longitude, density] format the 
following GMT command should be used:

For the 30s files: 

gmt grd2xyz 30s_UNB_TopoDens_2v02.grd -: > 30s_UNB_TopoDens_2v02.txt
gmt grd2xyz 30s_UNB_TopoDens_STD_2v02.grd -: > 30s_UNB_TopoDens_STD_2v02.txt

Likewise for the 5m and 1d files:

gmt grd2xyz 5m_UNB_TopoDens_2v02.grd -: > 5m_UNB_TopoDens_2v02.txt
gmt grd2xyz 5m_UNB_TopoDens_STD_2v02.grd -: > 5m_UNB_TopoDens_STD_2v02.txt

gmt grd2xyz 1d_UNB_TopoDens_2v02.grd -: > 1d_UNB_TopoDens_2v02.txt
gmt grd2xyz 1d_UNB_TopoDens_STD_2v02.grd -: > 1d_UNB_TopoDens_STD_2v02.txt

**Please note that the GMT conversion changes the precision level of the output file; 
all density values are only accurate to the 4th decimal place and output files should
be rounded to this level for optimal usage.**

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Creating a new Sub-region

Because of the size of the "unpacked" 30s density and standard deviation files, it may
be useful to extract only a sub-region of the global file before unpacking it into a
text file. In order to do this, the following GMT command should be used:

gmt grdcut 30s_UNB_TopoDensT_2v02.grd -GOUTPUTFILENAME.grd -RMIN_LONG/MAX_LONG/MIN_LAT/MAX_LAT

Example: 
In order to extract values only over Canada ([30,85] Latitude [215,310] Longitude)
the following command would be used:

gmt grdcut 30s_UNB_TopoDens_2v02.grd -G30s_UNB_TopoDens_2v02_Canada.grd -R215/310/30/85

The output file 30s_UNB_TopoDens_2v02_Canada.grd can then be unpacked using the command
found in the previous section.