D-8 
DATA IMPORT BUTTON 
Click the Data Import Button to select the Data Import screen. On this screen, click 
the “Get File Name” button to select the data file that contains the data that are to be 
interpolated (Figure D-7). The default file extension for data files is .d3d. d3d files 
include the X and Y coordinates (UTM Zone 18, NAD83 is recommended for inter¬ 
polation. These are also required for the graphics tools.) 
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Figure D-7. Data Import screen, "Get File Name" window. Select a data 
file (.d3d) for analysis. 
Once the file has been selected, the other fields on this screen will populate with 
information about the data file, including, start and end dates of the data, the number 
of observations, the date the file was created, the parameter name and code, and title 
(Figure D-8). Normally data do not need to be transformed, however, some data such 
as chlorophyll orTSS should be transformed with the log-transform to normalize the 
data. The data are transformed as they are read into the interpolator and the results 
are back-transformed to the original units in the output file. If the parameter is to be 
transformed by the natural log transform, any data values that are negative or zero 
will be set to a value of 0.0001. If the parameter is to be transformed by the square 
root transform, any data values that are negative will be set to 0.0. 
Two buttons at the bottom of the screen can be used to convert latitude and longitude 
coordinates to UTM coordinates, which are recommended for interpolation (Figures 
D-9, D-10). The first converts the longitude and latitude coordinates in d3d formatted 
files to UTM coordinates, and vice versa. This is handy for checking data locations on 
maps. The second converts individual longitudes and latitudes to and from UTM coor¬ 
dinates. NAD27 to NAD83 conversion is not supported in this code. Improper use of 
NAD27 or NAD83 can result in coordinate errors in the 100 to 300 meter range. 
appendix d 
User Guide and Documentation for the Chesapeake Bay Interpolator 
