+on a single tower may be generated by \fBSPLAT!\fP.
+.SH LONGLEY-RICE PATH LOSS ANALYSIS
+If the \fI-c\fP switch is replaced by a \fI-L\fP switch, a
+Longley-Rice path loss map for a transmitter site may be generated:
+
+\fCsplat -t wnjt -L 30.0 -s cities.dat -b co34_d00.dat -o path_loss_map\fR
+
+In this mode, \fBSPLAT!\fP generates a multi-color map illustrating
+expected signal levels (path loss) in areas surrounding the transmitter
+site. A legend at the bottom of the map correlates each color with a
+specific path loss range in decibels.
+
+The Longley-Rice analysis range may be modified to a user-specific
+value using the \fI-R\fP switch. The argument must be given in miles
+(or kilometers if the \fI-metric\fP switch is used). If a range wider
+than the generated topographic map is specified, \fBSPLAT!\fP will
+perform Longley-Rice path loss calculations between all four corners
+of the area prediction map.
+
+The \fI-db\fP switch allows a constraint to be placed on the maximum
+path loss region plotted on the map. A maximum path loss between 80
+and 230 dB may be specified using this switch. For example, if a path
+loss beyond -140 dB is irrelevant to the survey being conducted,
+\fBSPLAT!\fP's path loss plot can be constrained to the region
+bounded by the 140 dB attenuation contour as follows:
+
+\fCsplat -t wnjt -L 30.0 -s cities.dat -b co34_d00.dat -db 140 -o plot.ppm\fR
+
+.SH ANTENNA RADIATION PATTERN PARAMETERS
+Normalized field voltage patterns for a transmitting antenna's horizontal
+and vertical planes are imported automatically into \fBSPLAT!\fP when a
+Longley-Rice coverage analysis is performed. Antenna pattern data is
+read from a pair of files having the same base name as the transmitter
+and LRP files, but with \fI.az\fP and \fI.el\fP extensions for azimuth
+and elevation pattern files, respectively. Specifications regarding
+pattern rotation (if any) and mechanical beam tilt and tilt direction
+(if any) are also contained within \fBSPLAT!\fP antenna pattern files.
+
+For example, the first few lines of a \fBSPLAT!\fP azimuth pattern file
+might appear as follows (\fIkvea.az\fP):
+\fC
+ 183.0
+ 0 0.8950590
+ 1 0.8966406
+ 2 0.8981447
+ 3 0.8995795
+ 4 0.9009535
+ 5 0.9022749
+ 6 0.9035517
+ 7 0.9047923
+ 8 0.9060051
+\fR
+The first line of the \fI.az\fP file specifies the amount of azimuthal
+pattern rotation (measured clockwise in degrees from True North) to be
+applied by \fBSPLAT!\fP to the data contained in the \fI.az\fP file.
+This is followed by azimuth headings (0 to 360 degrees) and their associated
+normalized field patterns (0.000 to 1.000) separated by whitespace.
+
+The structure of \fBSPLAT!\fP elevation pattern files is slightly different.
+The first line of the \fI.el\fP file specifies the amount of mechanical
+beam tilt applied to the antenna. Note that a \fIdownward tilt\fP
+(below the horizon) is expressed as a \fIpositive angle\fP, while an
+\fIupward tilt\fP (above the horizon) is expressed as a \fInegative angle\fP.
+This data is followed by the azimuthal direction of the tilt, separated by
+whitespace.
+
+The remainder of the file consists of elevation angles and their
+corresponding normalized voltage radiation pattern (0.000 to 1.000)
+values separated by whitespace. Elevation angles must be specified
+over a -10.0 to +90.0 degree range. As was the convention with mechanical
+beamtilt, \fInegative elevation angles\fP are used to represent elevations
+\fIabove the horizon\fP, while \fIpositive angles\fP represents elevations
+\fIbelow the horizon\fP.
+
+For example, the first few lines a \fBSPLAT!\fP elevation pattern file
+might appear as follows (\fIkvea.el\fP):
+\fC
+ 1.1 130.0
+ -10.0 0.172
+ -9.5 0.109
+ -9.0 0.115
+ -8.5 0.155
+ -8.0 0.157
+ -7.5 0.104
+ -7.0 0.029
+ -6.5 0.109
+ -6.0 0.185
+\fR
+In this example, the antenna is mechanically tilted downward 1.1 degrees
+towards an azimuth of 130.0 degrees.
+
+For best results, the resolution of azimuth pattern data should be
+specified to the nearest degree azimuth, and elevation pattern data
+resolution should be specified to the nearest 0.01 degrees. If the
+pattern data specified does not reach this level of resolution,
+\fBSPLAT!\fP will interpolate the values provided to determine the
+data at the required resolution, although this may result in a loss
+in accuracy.
+
+.SH IMPORTING AND EXPORTING REGIONAL PATH LOSS CONTOUR DATA
+Performing a Longley-Rice coverage analysis can be a very time
+consuming process, especially if the analysis is repeated repeatedly
+to discover what effects changes to the antenna radiation patterns
+make to the predicted coverage area.
+
+This process can be expedited by exporting the Longley-Rice
+regional path loss contour data to an output file, modifying the
+path loss data externally to incorporate antenna pattern effects,
+and then importing the modified path loss data back into \fBSPLAT!\fP
+to rapidly produce a revised path loss map.
+
+For example, a path loss output file can be generated by \fBSPLAT!\fP
+for a receive site 30 feet above ground level over a 50 mile radius
+surrounding a transmitter site to a maximum path loss of 140 dB using
+the following syntax:
+
+\fCsplat -t kvea -L 30.0 -R 50.0 -db 140 -plo pathloss.dat\fR
+
+\fBSPLAT!\fP path loss output files often exceed 100 megabytes in size.
+They contain information relating to the boundaries of region they describe
+followed by latitudes (degrees North), longitudes (degrees West), azimuths,
+elevations (to the first obstruction), and path loss figures (dB) for a
+series of specific points that comprise the region surrounding the
+transmitter site. The first few lines of a \fBSPLAT!\fP path loss
+output file take on the following appearance (\fIpathloss.dat\fP):
+\fC
+ 119, 117 ; max_west, min_west
+ 35, 33 ; max_north, min_north
+ 34.2265434, 118.0631104, 48.171, -37.461, 67.70
+ 34.2270355, 118.0624390, 48.262, -26.212, 73.72
+ 34.2280197, 118.0611038, 48.269, -14.951, 79.74
+ 34.2285156, 118.0604401, 48.207, -11.351, 81.68
+ 34.2290077, 118.0597687, 48.240, -10.518, 83.26
+ 34.2294998, 118.0591049, 48.225, 23.201, 84.60
+ 34.2304878, 118.0577698, 48.213, 15.769, 137.84
+ 34.2309799, 118.0570984, 48.234, 15.965, 151.54
+ 34.2314720, 118.0564346, 48.224, 16.520, 149.45
+ 34.2319679, 118.0557632, 48.223, 15.588, 151.61
+ 34.2329521, 118.0544281, 48.230, 13.889, 135.45
+ 34.2334442, 118.0537643, 48.223, 11.693, 137.37
+ 34.2339401, 118.0530930, 48.222, 14.050, 126.32
+ 34.2344322, 118.0524292, 48.216, 16.274, 156.28
+ 34.2354164, 118.0510941, 48.222, 15.058, 152.65
+ 34.2359123, 118.0504227, 48.221, 16.215, 158.57
+ 34.2364044, 118.0497589, 48.216, 15.024, 157.30
+ 34.2368965, 118.0490875, 48.225, 17.184, 156.36
+\fR
+It is not uncommon for \fBSPLAT!\fP path loss files to contain as
+many as 3 million or more lines of data. Comments can be placed in
+the file if they are proceeded by a semicolon character. The \fBvim\fP
+text editor has proven capable of editing files of this size.
+
+Note as was the case in the antenna pattern files, negative elevation
+angles refer to upward tilt (above the horizon), while positive angles
+refer to downward tilt (below the horizon). These angles refer to the
+elevation to the receiving antenna at the height above ground level
+specified using the \fI-L\fP switch \fIif\fP the path between transmitter
+and receiver is unobstructed. If the path between the transmitter
+and receiver is obstructed, then the elevation angle to the first
+obstruction is returned by \fBSPLAT!\fP. This is because
+the Longley-Rice model considers the energy reaching a distant point
+over an obstructed path as a derivative of the energy scattered from
+the top of the first obstruction, only. Since energy cannot reach
+the obstructed location directly, the actual elevation angle to that
+point is irrelevant.
+
+When modifying \fBSPLAT!\fP path loss files to reflect antenna
+pattern data, \fIonly the last column (path loss)\fP should be amended
+to reflect the antenna's normalized gain at the azimuth and elevation
+angles specified in the file. (At this time, programs and scripts
+capable of performing this operation are left as an exercise for
+the user.)
+
+Modified path loss maps can be imported back into \fBSPLAT!\fP for
+generating revised coverage maps:
+
+\fCsplat -t kvea -pli pathloss.dat -s city.dat -b county.dat -o map.ppm\fR
+
+\fBSPLAT!\fP path loss files can also be used for conducting coverage or
+interference studies outside of \fBSPLAT!\fP.
+.SH USER-DEFINED TERRAIN INPUT FILES
+A user-defined terrain file is a user-generated text file containing latitudes,
+longitudes, and heights above ground level of specific terrain features believed
+to be of importance to the \fBSPLAT!\fP analysis being conducted, but noticeably
+absent from the SDF files being used. A user-defined terrain file is imported
+into a \fBSPLAT!\fP analysis using the \fI-udt\fP switch:
+
+\fC splat -t tx_site -r rx_site -udt udt_file.txt -o map.ppm\fR
+
+A user-defined terrain file has the following appearance and structure:
+\fC
+ 40.32180556, 74.1325, 100.0 meters
+ 40.321805, 74.1315, 300.0
+ 40.3218055, 74.1305, 100.0 meters
+\fR
+Terrain height is interpreted as being described in feet above ground
+level unless followed by the word \fImeters\fP, and is added \fIon top of\fP
+the terrain specified in the SDF data for the locations specified. Be
+aware that each user-defined terrain feature specified will be interpreted
+as being 3-arc seconds in both latitude and longitude. Features described
+in the user-defined terrain file that overlap previously defined features
+in the file are ignored by \fBSPLAT!\fP.
+.SH SIMPLE TOPOGRAPHIC MAP GENERATION
+In certain situations it may be desirable to generate a topographic map