-.TH SPLAT! 1 "20 January 2004" "KD2BD Software" "KD2BD Software"
+.TH SPLAT! 1 "02 March 2006" "KD2BD Software" "KD2BD Software"
.SH NAME
-splat \- A \fBS\fPignal \fBP\fPropagation, \fBL\fPoss, \fBA\fPnd \fBT\fPerrain analysis tool
+splat \- An RF \fBS\fPignal \fBP\fPropagation, \fBL\fPoss, \fBA\fPnd \fBT\fPerrain analysis tool
.SH SYNOPSIS
-splat [-t \fItransmitter_site.qth\fP]
-[-r \fIreceiver_site.qth\fP]
-[-c \fIrx_antenna_height_for_los_coverage_analysis (feet) (float)\fP]
-[-L \fIrx_antenna_height_for_Longley-Rice_coverage_analysis (feet) (float)\fP]
-[-p \fIterrain_profile.ext\fP]
-[-e \fIelevation_profile.ext\fP]
-[-h \fIheight_profile.ext\fP]
-[-l \fILongley-Rice_profile.ext\fP]
-[-o \fItopographic_map_filename.ppm\fP]
-[-b \fIcartographic_boundary_filename.dat\fP]
-[-s \fIsite/city_database.dat\fP]
-[-d \fIsdf_directory_path\fP]
-[-m \fIearth_radius_multiplier (float)\fP]
-[-R \fImaximum_coverage_range (for -c or -L) (miles) (float)\fP]
+splat [-t \fItransmitter_site.qth\fP]
+[-r \fIreceiver_site.qth\fP]
+[-c \fIrx_antenna_height_for_los_coverage_analysis (feet) (float)\fP]
+[-L \fIrx_antenna_height_for_Longley-Rice_coverage_analysis (feet) (float)\fP]
+[-p \fIterrain_profile.ext\fP]
+[-e \fIelevation_profile.ext\fP]
+[-h \fIheight_profile.ext\fP]
+[-l \fILongley-Rice_profile.ext\fP]
+[-o \fItopographic_map_filename.ppm\fP]
+[-b \fIcartographic_boundary_filename.dat\fP]
+[-s \fIsite/city_database.dat\fP]
+[-d \fIsdf_directory_path\fP]
+[-m \fIearth_radius_multiplier (float)\fP]
+[-R \fImaximum_coverage_range (for -c or -L) (miles) (float)\fP]
+[-dB \fImaximum attenuation contour to display on path loss maps (80-230 dB)\fP]
[-n]
[-N]
.SH DESCRIPTION
-\fBSPLAT!\fP is a simple, yet powerful terrain analysis tool written
-for Unix and Linux-based workstations. \fBSPLAT!\fP is free software.
-Redistribution and/or modification is permitted under the terms of the
-GNU General Public License as published by the Free Software Foundation,
-either version 2 of the License or any later version. Adoption of
-\fBSPLAT!\fP source code in proprietary or closed-source applications
-is a violation of this license, and is \fBstrictly\fP forbidden.
+\fBSPLAT!\fP is a powerful terrestrial RF propagation and terrain
+analysis tool covering the spectrum between 20 MHz and 20 GHz. It
+is designed for operation on Unix and Linux-based workstations.
+\fBSPLAT!\fP is free software. Redistribution and/or modification
+is permitted under the terms of the GNU General Public License as
+published by the Free Software Foundation, either version 2 of the
+License or any later version. Adoption of \fBSPLAT!\fP source code
+in proprietary or closed-source applications is a violation of this
+license, and is \fBstrictly\fP forbidden.
\fBSPLAT!\fP is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY, without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
.SH INTRODUCTION
-\fBSPLAT!\fP is a terrestrial RF propagation analysis tool for the
-spectrum between 20 MHz and 20 GHz, and provides information of
-interest to communication system designers and site engineers.
-\fBSPLAT!\fP determines great circle distances and bearings between
-sites, antenna elevation angles (uptilt), depression angles
-(downtilt), antenna height above mean sea level, antenna height
-above average terrain, bearings and distances to known obstructions,
-Longley-Rice path loss, and minimum antenna height requirements
-needed to establish line-of-sight communication paths absent of
-obstructions due to terrain. \fBSPLAT!\fP produces reports, graphs,
+Applications of \fBSPLAT!\fP include the visualization, design, and
+link budget analysis of wireless Wide Area Networks (WANs), commercial
+and amateur radio communication systems above 20 MHz, microwave links,
+frequency coordination, and the determination of analog and digital
+terrestrial radio and television contour regions.
+
+\fBSPLAT!\fP provides RF site engineering data such as great circle
+distances and bearings between sites, antenna elevation angles (uptilt),
+depression angles (downtilt), antenna height above mean sea level,
+antenna height above average terrain, bearings and distances to known
+obstructions, Longley-Rice path attenuation, and minimum antenna height
+requirements needed to establish line-of-sight communication paths absent
+of obstructions due to terrain. \fBSPLAT!\fP produces reports, graphs,
and highly detailed and carefully annotated topographic maps depicting
line-of-sight paths, path loss, and expected coverage areas of
transmitters and repeater systems. When performing line-of-sight
are employed, \fBSPLAT!\fP determines individual and mutual areas
of coverage within the network specified.
-\fBSPLAT!\fP operates in two modes: \fIpoint-to-point mode\fP, and
-\fIarea prediction mode\fP. These modes may be invoked using either
+\fBSPLAT!\fP operates in two distinct modes: \fIpoint-to-point mode\fP,
+and \fIarea prediction mode\fP, and may be invoked using either
line-of-sight (LOS) or Irregular Terrain (ITM) propagation models.
True Earth, four-thirds Earth, or any other Earth radius may be
specified by the user when performing line-of-sight analysis.
.SH INPUT FILES
\fBSPLAT!\fP is a command-line driven application, and reads input
-data through a number of data files. Each has its own format. Some
-files are mandatory for successful execution of the program, while
-others are optional. Mandatory files include SPLAT Data Files (SDF
-files), site location files (QTH files), and Longley-Rice model
-parameter files (LRP files). Optional files include city/site
-location files, and cartographic boundary files.
+data through a number of data files. Some files are mandatory for
+successful execution of the program, while others are optional.
+Mandatory files include SPLAT Data Files (SDF files), site location
+files (QTH files), and Longley-Rice model parameter files (LRP files).
+Optional files include city/site location files, and cartographic
+boundary files.
.SH SPLAT DATA FILES
\fBSPLAT!\fP imports topographic data in the form of SPLAT Data Files
-(SDFs) that may be generated from a number of information sources. In
-the United States, SPLAT Data Files are most often derived from U.S.
+(SDFs). These files may be generated from a number of information sources.
+In the United States, SPLAT Data Files can be generated through U.S.
Geological Survey Digital Elevation Models (DEMs) using the \fBusgs2sdf\fP
utility included with \fBSPLAT!\fP. USGS Digital Elevation Models
-compatible with this utility are available at no cost via the Internet at:
-\fIhttp://edcsgs9.cr.usgs.gov/glis/hyper/guide/1_dgr_demfig/index1m.html\fP.
-
-SPLAT Data Files contain topographic elevations to the nearest meter
-above mean sea level for 1-degree by 1-degree regions of the earth with
-a resolution of 3-arc seconds. SDF files can be read in either standard
-format (\fI.sdf\fP) as generated by the \fBusgs2sdf\fP utility, or in
-bzip2 compressed format (\fI.sdf.bz2\fP). Since uncompressed files can
-be slightly faster to load than compressed files, \fBSPLAT!\fP searches
-for the needed SDF data in uncompressed format first. If such data cannot
-located, then \fBSPLAT!\fP tries to read the data in bzip2 compressed
+compatible with this utility may be downloaded from:
+\fIhttp://edcftp.cr.usgs.gov/pub/data/DEM/250/\fP.
+
+Significantly better resolution can be obtained through the use
+of SRTM-3 Version 2 digital elevation models. These models are the
+result of the STS-99 Space Shuttle Radar Topography Mission, and are
+available for most populated regions of the Earth. SPLAT Data Files
+may be generated from SRTM data using the included \fBsrtm2sdf\fP utility.
+SRTM-3 Version 2 data may be obtained through anonymous FTP from:
+\fIftp://e0srp01u.ecs.nasa.gov:21/srtm/version2/\fP
+
+Despite the higher accuracy that SRTM data has to offer, some voids
+in the data sets exist. When voids are detected, the \fBsrtm2sdf\fP
+utility replaces them with corresponding data found in existing SDF
+files (that were presumably created from earlier USGS data through the
+\fBusgs2sdf\fP utility). If USGS-derived SDF data is not available, voids
+are handled through adjacent pixel averaging, or direct replacement.
+
+SPLAT Data Files contain integer value topographic elevations (in meters)
+referenced to mean sea level for 1-degree by 1-degree regions of the
+earth with a resolution of 3-arc seconds. SDF files can be read in
+either standard format (\fI.sdf\fP) as generated by the \fBusgs2sdf\fP
+and \fBsrtm2sdf\fP utilities, or in bzip2 compressed format
+(\fI.sdf.bz2\fP). Since uncompressed files can be processed slightly
+faster than files that have been compressed, \fBSPLAT!\fP searches for
+the needed SDF data in uncompressed format first. If uncompressed data
+cannot located, \fBSPLAT!\fP then searches for data in bzip2 compressed
format. If no compressed SDF files can be found for the region requested,
-\fBSPLAT!\fP assumes the region is over water or outside the United States,
-and will assign an elevation of sea-level to these areas. This feature
-of \fBSPLAT!\fP makes it possible to perform path analysis not only over
-land, but also between coastal areas not represented by USGS Digital
-Elevation Model Data since they are devoid of any land masses. However,
-this behavior of \fBSPLAT!\fP underscores the importance of having all
-the SDF files required for the region being analyzed if meaningful
-results are to be expected.
+\fBSPLAT!\fP assumes the region is over water, and will assign an
+elevation of sea-level to these areas.
+
+This feature of \fBSPLAT!\fP makes it possible to perform path analysis
+not only over land, but also between coastal areas not represented by
+Digital Elevation Model data. This behavior of \fBSPLAT!\fP underscores
+the importance of having all the SDF files required for the region being
+analyzed if meaningful results are to be expected.
.SH SITE LOCATION (QTH) FILES
\fBSPLAT!\fP imports site location information of transmitter and receiver
sites analyzed by the program from ASCII files having a \fI.qth\fP extension.
-QTH files contain the site's name, the site's latitude (in degrees North),
-the site's longitude (in degrees West), and the site's antenna height
-above ground level (AGL). A single line-feed character separates each
-field. The antenna height is assumed to be specified in feet unless
-followed by the letter \fIm\fP or the word \fImeters\fP in either upper
-or lower case. Latitude and longitude information may be expressed in
-either decimal format (74.6889) or degree, minute, second (DMS)
-format (74 41 20.0).
+QTH files contain the site's name, the site's latitude (positive if North
+of the equator, negative if South), the site's longitude (in degrees West,
+0 to 360 degrees), and the site's antenna height above ground level (AGL).
+A single line-feed character separates each field. The antenna height is
+assumed to be specified in feet unless followed by the letter \fIm\fP or
+the word \fImeters\fP in either upper or lower case. Latitude and
+longitude information may be expressed in either decimal format (74.6889)
+or degree, minute, second (DMS) format (74 41 20.0).
For example, a site location file describing television station WNJT,
Trenton, NJ (\fIwnjt.qth\fP) might read as follows:
represented by its own site location (QTH) file.
.SH LONGLEY-RICE PARAMETER (LRP) FILES
\fBSPLAT!\fP imports Longley-Rice model parameter data from files having
-the same base name as the transmitter site QTH file, but carrying a \fI.lrp\fP
+the same base name as the transmitter site QTH file, but with a \fI.lrp\fP
extension, thus providing simple and accurate correlation between these
associated data sets. The format for the Longley-Rice model parameter
files is as follows (\fIwnjt.lrp\fP):
the file "splat.lrp". If this file cannot be found, then the default
parameters listed above will be assigned by \fBSPLAT!\fP and a
corresponding "splat.lrp" file containing this data will be written
-to the current working directory.
+to the current working directory. "splat.lrp" can then be edited
+by the user as needed.
Typical Earth dielectric constants and conductivity values are as
follows:
United States. Isotropic antennas are assumed.
For further information on these parameters, see:
-\fIhttp://elbert.its.bldrdoc.gov/itm.html\fP and
+\fIhttp://flattop.its.bldrdoc.gov/itm.html\fP and
\fIhttp://www.softwright.com/faq/engineering/prop_longley_rice.html\fP
.SH CITY LOCATION FILES
The names and locations of cities, tower sites, or other points of interest
-may imported and be plotted on topographic maps generated by \fBSPLAT!\fP.
+may be imported and plotted on topographic maps generated by \fBSPLAT!\fP.
\fBSPLAT!\fP imports the names of cities and locations from ASCII files
containing the location's name, the location's latitude, and the location's
longitude. Each field is separated by a comma. Each record is separated
Totowa, 40.906160, 74.223310
Trenton, 40.219922, 74.754665
\fR
-A total of five separate city data files may be imported at a time.
-There is no limit to the size of these files. \fBSPLAT!\fP reads city
-data sequentially, and plots only those locations whose positions do
-not conflict with previously plotted locations when generating
-topographic maps.
+A total of five separate city data files may be imported at a time,
+and there is no limit to the size of these files. \fBSPLAT!\fP reads
+city data on a "first come/first served" basis, and plots only those
+locations whose annotations do not conflict with annotations of
+locations plotted earlier during \fBSPLAT\fP's execution. This behavior
+minimizes clutter in \fBSPLAT!\fP generated topographic maps, but also
+mandates that important locations be placed toward the beginning of
+the first city data file, and disposable locations be positioned
+further down the list or in subsequent data files.
City data files may be generated manually using any text editor,
imported from other sources, or derived from data available from the
.SH PROGRAM OPERATION
\fBSPLAT!\fP is invoked via the command-line using a series of switches
and arguments. Since \fBSPLAT!\fP is a CPU and memory intensive application,
-this type of interface minimizes overhead, and also lends itself well to
-scripted operations. \fBSPLAT!\fP's CPU and memory scheduling priority
-may be adjusted through the use of the Unix \fBnice\fP command.
+this type of interface minimizes overhead and lends itself well to
+scripted (batch) operations. \fBSPLAT!\fP's CPU and memory scheduling
+priority may be modified through the use of the Unix \fBnice\fP command.
The number and type of switches passed to \fBSPLAT!\fP determine its
mode of operation and method of output data generation. Nearly all
of \fBSPLAT!\fP's switches may be cascaded in any order on the command
-line when invoking the program to include all the features described
-by those switches when performing an analysis.
+line when invoking the program.
.SH POINT-TO-POINT ANALYSIS
\fBSPLAT!\fP may be used to perform line-of-sight terrain analysis
between two specified site locations. For example:
will indicate the minimum antenna height required for a line-of-sight
path to exist between the transmitter and receiver locations specified.
If the antenna must be raised a significant amount, this determination
-may take some time.
+may take some time. Note that the results provided are the \fIminimum\fP
+necessary for a line-of-sight path to exist, and do not take Fresnel
+zone clearance requirements into consideration.
-\fI.qth\fP extensions are assumed by \fBSPLAT!\fP for QTH files, and
+\fIqth\fP extensions are assumed by \fBSPLAT!\fP for QTH files, and
are optional when invoking the program. \fBSPLAT!\fP automatically
reads all SPLAT Data Files necessary to conduct the terrain analysis
-between the sites specified. By default, the location of SDF files
-is assumed to be in the current working directory unless a
-".splat_path" file is present under the user's home directory.
-If this file is present, it must contain the full directory path to
-the location of all the SDF files required by \fBSPLAT!\fP to perform
-its analysis for the region containing the transmitter and receiver
-sites specified. The path in this file must be of the form of a
+between the sites specified. \fBSPLAT!\fP searches for the needed
+SDF files in the current working directory first. If the needed
+files are not found, \fBSPLAT!\fP then searches in the path specified
+by the \fI-d\fP command-line switch:
+
+\fCsplat -t tx_site -r rx_site -d /cdrom/sdf/\fR
+
+An external directory path may be specified by placing a ".splat_path"
+file under the user's home directory. This file must contain the full
+directory path to the last resort location of all the SDF files. The
+path in the \fI$HOME/.splat_path\fP file must be of the form of a
single line of ASCII text:
\fC/opt/splat/sdf/\fR
-and may be generated with any text editor. The default path specified
-in the \fI$HOME/.splat_path\fP file may be overridden at any time using
-the \fI-d\fP switch:
-
-\fCsplat -t tx_site -r rx_site -d /cdrom/sdf/\fR
+and can be generated using any text editor.
A graph of the terrain profile between the receiver and transmitter
locations as a function of distance from the receiver can be generated
represented through brighter shades of gray. The dynamic range of
the image is scaled between the highest and lowest elevations present
in the map. The only exception to this is sea-level, which is
-represented in blue.
+represented using the color blue.
\fBSPLAT!\fP generated topographic maps are 24-bit TrueColor Portable
-PixMap (PPM) images, and may be viewed, edited, or converted to other
+PixMap (PPM) images. They may be viewed, edited, or converted to other
graphic formats by popular image viewing applications such as \fBxv\fP,
\fBThe GIMP\fP, \fBImageMagick\fP, and \fBXPaint\fP. PNG format is
highly recommended for lossless compressed storage of \fBSPLAT!\fP
of sites, and predict the regional coverage for each site specified.
In this mode, \fBSPLAT!\fP can generate a topographic map displaying
the geometric line-of-sight coverage area of the sites based on the
-location of each site, and the height of receive antenna wishing to
+location of each site and the height of receive antenna wishing to
communicate with the site in question. \fBSPLAT!\fP switches from
point-to-point analysis mode to area prediction mode when the \fI-c\fP
switch is invoked as follows:
\fCsplat -t wnjt -c 30.0 -m 1.333 -s cities.dat -b counties.dat -o map.ppm\fR
-An earth radius multiplier of 1.333 instructs \fBSPLAT!\fP to use
+An earth radius multiplier of 1.333 instructs \fBSPLAT!\fP to use
the "four-thirds earth" model for line-of-sight propagation analysis.
Any appropriate earth radius multiplier may be selected by the user.
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 tx_site -L 30.0 -s cities.dat -b co34_d00.dat -o path_loss_map\fR
+\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 level in decibels. Since Longley-Rice area
-prediction map generation is quite CPU intensive, provision for
+prediction map generation is very CPU intensive, provision for
limiting the analysis range is provided by the \fI-R\fP switch.
The argument must be given in miles. 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 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 DETERMINING MULTIPLE REGIONS OF COVERAGE
\fBSPLAT!\fP can also display line-of-sight coverage areas for as
many as four separate transmitter sites on a common topographic map.
Part 73.313(d). According to this definition, terrain elevations along
eight radials between 2 and 10 miles (3 and 16 kilometers) from the site
being analyzed are sampled and averaged for each 45 degrees of azimuth
-starting with True North. If one or more radials lie entirely over water,
+starting with True North. If one or more radials lie entirely over water
or over land outside the United States (areas for which no USGS topography
data is available), then those radials are omitted from the calculation
of average terrain. If part of a radial extends over a body of water or
lying over United States land is used in the determination of average
terrain.
+Note that SRTM elevation data, unlike older 3-arc second USGS data,
+extends beyond the borders of the United States. Therefore, HAAT
+results may not be in full compliance with FCC Part 73.313(d)
+in areas along the borders of the United States if the SDF files
+used by \fBSPLAT!\fP are SRTM-derived.
+
When performing point-to-point terrain analysis, \fBSPLAT!\fP determines
the antenna height above average terrain only if enough topographic
data has already been loaded by the program to perform the point-to-point
does not lie within 10 miles of the boundary of the topography data in
memory.
-When performing area prediction analysis, enough topography data is normally
-loaded by \fBSPLAT!\fP to perform average terrain calculations. Under
-such conditions, \fBSPLAT!\fP will provide the antenna height above
-average terrain as well as the average terrain above mean sea level
-for azimuths of 0, 45, 90, 135, 180, 225, 270, and 315 degrees, and
-include such information in the site report generated. If one or
-more of the eight radials surveyed fall over water or land outside
-the United States, \fBSPLAT!\fP reports \fINo Terrain\fP for those
-radial paths.
-.SH SETTING THE MAXIMUM SIZE OF AN ANALYSIS REGION
-\fBSPLAT!\fP reads SDF files into a series of memory "slots" as required
-within the structure of the program. Each "slot" holds one SDF file.
-Each SDF file represents a one degree by one degree region of terrain.
+When performing area prediction analysis, enough topography data is
+normally loaded by \fBSPLAT!\fP to perform average terrain calculations.
+Under such conditions, \fBSPLAT!\fP will provide the antenna height
+above average terrain as well as the average terrain above mean sea
+level for azimuths of 0, 45, 90, 135, 180, 225, 270, and 315 degrees,
+and include such information in the site report generated. If one or
+more of the eight radials surveyed fall over water, or over regions
+for which no SDF data is available, \fBSPLAT!\fP reports \fINo Terrain\fP
+for the radial paths affected.
+.SH RESTRICTING THE MAXIMUM SIZE OF AN ANALYSIS REGION
+\fBSPLAT!\fP reads SDF files as needed into a series of memory "slots"
+within the structure of the program. Each "slot" holds one SDF file
+representing a one degree by one degree region of terrain.
A \fI#define MAXSLOTS\fP statement in the first several lines of
\fIsplat.cpp\fP sets the maximum number of "slots" available for topography
data. It also sets the maximum size of the topographic maps generated by
\fBSPLAT!\fP. MAXSLOTS is set to 9 by default. If \fBSPLAT!\fP produces
a segmentation fault on start-up with this default, it is an indication
-that not enough RAM and/or virtual memory (swap space) are available to
-run \fBSPLAT!\fP with this number of MAXSLOTS. In this case, MAXSLOTS
-may be reduced to 4, although this will greatly limit the maximum region
-\fBSPLAT!\fP will be able to analyze. If 118 megabytes or more of total
-memory (swap space plus RAM) is available, then MAXSLOTS may be increased
-to 16. This will permit operation over a 4-degree by 4-degree region,
-which is sufficient for single antenna heights in excess of 10,000 feet
-above mean sea level, or point-to-point distances of over 1000 miles.
+that not enough RAM and/or virtual memory (swap space) is available to
+run \fBSPLAT!\fP with this number of MAXSLOTS. In situations where
+available memory is low, MAXSLOTS may be reduced to 4 with the understanding
+that this will greatly limit the maximum region \fBSPLAT!\fP will be able
+to analyze. If 118 megabytes or more of total memory (swap space plus
+RAM) is available, then MAXSLOTS may be increased to 16. This will
+permit operation over a 4-degree by 4-degree region, which is sufficient
+for single antenna heights in excess of 10,000 feet above mean sea
+level, or point-to-point distances of over 1000 miles.
.SH ADDITIONAL INFORMATION
Invoking \fBSPLAT!\fP without any arguments will display all the
command-line options available with the program along with a brief
The latest news and information regarding \fBSPLAT!\fP software is
available through the official \fBSPLAT!\fP software web page located
at: \fIhttp://www.qsl.net/kd2bd/splat.html\fP.
-.SH FILES
-.TP
-\fC$HOME/.splat_path\fR
-User-generated file containing the default path to the directory
-containing the SDF data files.
-.TP
-\fCsplat.lrp\fR
-Default Longley-Rice model parameters.
.SH AUTHORS
.TP
John A. Magliacane, KD2BD <\fIkd2bd@amsat.org\fP>
projects / debian / splat / blobdiff