/riodetrend

Remove trend of a digital elevation model (DEM) of rivers

Primary LanguagePythonMIT LicenseMIT

Riodetrend - Python Solution to Detrend Digital Elevation Model (DEM)

1. About Riodetrend

1.1 Purpose

Detrend a piecewise Digital Elevation Model (DEM) of a river.

1.2 Motivation

Detrended DEM is a valuable information for a variety of analyses in River Engineering such as flood simulations, sediments transports and river modelling.

However, most known software that remove the trend of DEMs require license.

Riodetrend is a open source tool that efficiently removes the trend of DEMs with approximately linear Thalweg. However, the tool is not limited to DEMs with approximately linear Thalwegs, since a DEM can be clipped into smaller pieces that have the desired linear overall shape.

1.3 Data Flow Diagram

In general terms, the algorithm first reads a raster (DEM) and a point shapefile (Thalweg) as a arrays. It fits a plane using the cardinal direction and elevation of Thalweg points. As a second step, DEM array and the plane are subtracted resulting in a detrended DEM array. Finally, the detrended array is converted back into a raster (see workflow below).

2. Run Riodetrend

2.1 Clone the repository

$ git clone https://github.com/ricardovobarros/riodetrend.git

2.2 Requiried packages Packages

  • matplotlib.pyplot
  • numpy
  • pandas
  • geopandas
  • gdal
  • os
  • glob
  • sys
  • time
  • logging

2.3 Run Example "geodata_example"

Before applying Riodetrend to your DEMs, you can run the provided example geodata_example to get a feeling how the tool works.

To run the example, just run detrender.py. The output (i.e., detrended rasters) will be saved inside the folder detrended_rasters. Additionally, graphs that demonstrate the process will be saved inside geodata_example/plots.

During the running, warnings and the step-by-step computation are shown on the prompt.

2.4 Run on your DEMs <-----

Riodetrend require only two inputs to run:

  • local file address containing as many DEMs (.tiff files) you want, AND
  • local file address containing the corresponding Thalweg(s) (.shp files) to the DEMs.

In addition, the DEMS and shapefles, must be enumerated accordantly, as shown in the example folders geodata_example/rasters and geodata_example/shapefiles (e.g., raster_1 correponds to thalweg_1)

1.Input Raster

  • DEM of the river should not have tributaries. It must have only on main path of the river.
  • Clip your DEM in a optimized way. That means, this toll won't be able to detrend the DEM if the clipped raster files are curved. Please see examples in the folder geodata_example.

2. Input Shape

Follow the step-by-step below to create a desirable shape file input to run Detrender Tool.

The shapefiles do not contain the information of the elevation (z). Then it will be necessary to obtain this data from the DEM and relate them to the corresponding coordinates (X,Y) from the shapefile. This process can be done using the Field Calculator, as shown in following steps:

  1. Open a piecewise DEM in (QGIS).
  2. Create a Shape Line with the same projection of DEM.
  3. Use the tool from SAGA Gradient Vector from Surface to create a gradient vector field on the DEM.
  4. Use the provided DEM_style to paint the DEM. In raster file go to: properties>>style>>load style and choose DEM_style
  5. Still in properties, inside Band Rendering, change the max and min values to better fit the style on the DEM. Press ok.
  6. With the help of the style and the gradient vector filed draw a Shape Line representing the Thalweg of the DEM.
  7. Use the Tool Points Along Geometry and choose the previous created line as Input Layer. Define the distance as the larger pixel size of the DEM
  8. To save the elevation of the pixels immediately below the Shape points do the following:
    1. Select the created Shape Points and open Captura de Tela 2021-02-23 às 19 15 04 Field Caculator (Upper part, on the right of "ToolBox" button)
    2. Inside Field Caculator create a new field, as shown in the Figure 1, with the following properties:
      1. Choose the function "Expression" >> "Rasters" >> "raster_value"
        1. raster_value(DEM name, DEM band number, XY value of Shape Points)
      2. Output field name = "z" (it must be letter 'z' in lower case)
      3. Output field type = Decimal number (real)

Captura de Tela 2021-02-23 às 19 35 24
Figure 1. Creating Field named 'z' which saves
the elevation values of DEM's pixels located at
the exact Shape Point

Execution

- From the Terminal

python detrender.py [(rasters'_file), (shapes'_file), (print_boolean = 1) (band = 1), (detended_limit=10**(-3))]

  • rasters' file: (STRING) path-like of the folder in the system that contains all raster files (.tif) to be detrended
  • shapes' file: (STRING) path-like string of the folder in the system that contains all shape files (.shp)
  • print_boolean: (Optional INT, default=1) choose 1 to plot all figures related to the de trend process. Choose 0 to not plot it.
  • band: (Optional INT, default=1) band of the raster, in which is locates the elations of the pixels.
  • detrended_limit: (Optional FLOAT, default=10**-3) limit used to validate a detrended raster is flat enough to be considered detrended.

One folder named detrend_rasters will be automatic created at the save location of the folder containing the raster files.
If print_boolan = 1, one folder named detrender_plotter will be automatic created at the save location fo the folder containing the raster files.
The path to the folders should not have space on it.