7. A simple first example: extracting typical metrics

Here we explain how to run a simple driver: extract_basin_metrics.cpp

This driver extracts the following derived rasters from a user supplied .flt raster

• A filled raster, with _fill in the filename
• A hillshade raster, with _hs in the filename
• A slope raster, with _slope in the filename. This is calculated using a polynomial fit.
• A curvature raster, with _curv in the filename. This is calculated using a polynomial fit.
• A tangential curvature raster, with _tan_curv in the filename. This is calculated using a polynomial fit.
• A contributing pixel raster, with _CP in the filename. This is calculated using D8 with the Fastscape (Braun and Willett, Geomorphology 2013) algorithm.
• A DInfinity drainage area raster, with _DinfDA in the filename. Calculated based on the D-infinity algorithm (Tarbonton, 1997, WRR).
• A flow distance raster, with _FD in the filename. Derived from D8 flow routing.

7.1. Getting your raster into the correct format

You will need to get data that you have downloaded into a format LSDTopoToolbox can understand, namely the .flt format.

You can do this with arcmap; (read this: Converting data from ArcMap), or with GDAL (read this: Translating your raster into something that can be used by LSDTopoToolbox).

You can also do it with QGIS.

7.2. Compiling the driver function

You will need to download all of the code. This will have a directory with the objects (their names start with LSD).

Within the directory with the objects, there will be two additional directories:

• driver_functions
• TNT

The TNT folder contains routines for linear algebra, and it is made by NIST, you can happily do everything in LSDTopoToolbox without ever knowing anything about it, but if you want you can read what it is here: TNT homepage.

1. First, go into the driver function folder

2. Next, type:

   make -f extract_typical_metrics.make

   in a terminal.

3. You will get a bunch of messages but at the end your code will have compiled.

7.3. Running the driver function

Okay, now you are ready to run the driver function. You’ll need to run the function from the directory where the compiled code is located (extract_typical_metrics.exe), but it can work on data in some arbitrary location.

1. You run the code with the command ./extract_typical_metrics.exe pathname_of_data name_of_DEM filetype

• The pathname_of_data is just the path to where your data is stored, so for example I put some data into a folder with the path /home/smudd/topographic_tools/LSDRaster_local/Data/Chile/lat28p5/. IMPORTANT You MUST remember to put a / at the end of your pathname.
• The filename is the PREFIX of your DEM, so if your DEM is called lat_26p5_flt.flt then the name_of_DEM is lat_26p5_flt (that is, without the .flt at the end).
• The file type. Right now the only options are flt and asc. You do not include the full stop (i.e., .asc will not work).

2. This will write out a bunch of rasters to the folder indicated by pathname_of_data. It choses default parameters for the computations, these are:

• The threshold number of pixels that generate a channel.
• The search radius of the window for polynomial surface fitting.

3. Alternatively, you can write a file called topo_metrics.param that sits in the same directory as your DEM and has the threshold and the window_radius in plain text, separated by a space.