RiverTools Grid (RTG) Format
RiverTools Grids (RTG) are binary files with no header that
store a 2D array (or grid) that is the same size as the
DEM (*_DEM.rtg) they were derived from. Their dimensions,
georeferencing and other information are identical to the DEM,
except possibly for their data type. Values in the file are
stored in row major order; that is, values for the first (north)
row are followed by values for the second row, and so on.
The filesize for an RTG file is always equal to the product:
filesize = (ncols x nrows x BPE)
where BPE is the number of Bytes Per Element in the 2D array.
The possible data types for an RTG file are `BYTE', `INTEGER',
`LONG', `FLOAT', and `DOUBLE'. The corresponding values of BPE
are 1, 2, 4, 4, and 8. Each RTG file has a data type that is
appropriate for the range of possible values that array can
contain. This use of the most "economical" data type results
in more efficient use of disk space and faster access times.
Given the number of rows and columns in the DEM (nrows and
ncols), the data type of an RTG file can be deduced from its
filesize in all cases except when BPE is equal to 4. In this
case, the data type could be either LONG or FLOAT, and
additional information is required in order to determine
which one. A standard, recognized filename extension is one
method for deciding between these two data types.
Routines in the Extract menu create RTG files from other
RTG files, such as the initial DEM (*_DEM.rtg). For example, the
Extract -> Flow Grid routine will create a copy of the DEM
with the extension "_rawDEM.rtg" which it will leave unaltered,
and will then fill depressions in the file with extension
"_DEM.rtg". This routine will then go on to create a D8 flow
grid with extension "_flow.rtg" from the depressionless DEM
grid. This D8 flow grid is then used by other routines in
the Extract menu to create additional RTG files.
| Attribute |
File Extension |
Data Type |
| Area |
"_area.rtg" |
FLOAT or LONG |
| Curvature |
"_curv.rtg" |
FLOAT |
| Elevation |
"_DEM.rtg" |
any type |
| DInf Flow Angle |
"_dinf.rtg" |
DOUBLE |
| DInf Area |
"_dinfarea.rtg" |
DOUBLE |
| DInf Slope |
"_dinfslope.rtg" |
DOUBLE |
| Flow Distance |
"_FD.rtg" |
FLOAT |
| D8 Flow Codes |
"_flow.rtg" |
BYTE |
| Imposed grad. DEM |
"_imposed_DEM.rtg" |
FLOAT |
| Number of D8 Kids |
"_nkids.rtg" |
BYTE |
| HS Stream Order |
"_order.rtg" |
BYTE |
| Raw Elevations |
"_rawDEM.rtg" |
any type |
| Watershed units |
"_sides.rtg" |
LONG |
| Local D8 slope |
"_slope.rtg" |
FLOAT |
| Topo. index |
"_TI.rtg" |
FLOAT |
| Pit basin mask |
"_TMPmask.rtg" |
LONG |
There are several RiverTools commands that can be used for
working with RTG files. These require access to the IDL command
line, which is available with the RiverTools+IDL combination but
not with RiverTools itself. These include:
- RT_Read_Grid
- RT_Check_Grid_Type
- RT_Read_Subgrid
- RT_Write_Subgrid
- RT_Read_RTM_As_Grid
- RT_Get_Available_DEMs
- RT_Get_Available_Grids
These are fully documented in the
RiverTools Command Reference,
which can be downloaded from the
Downloads page.
The Extract menu also provides access to many routines for
creating RTG files.
Copyright (c) 1998-2008, Rivix, LLC. All rights reserved.
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