Waterbody enhancement using shape files

Strong reflections and changing appearance due its moving surface prohibit the accurate reconstruction of waterbodies from images employing stereo vision methods.

In order to acquire highest quality True Orthos and Meshes, SURE software provides the possibility to crop & replace sparse and noisy data generated on water bodies with smooth data interpolated from 3D polygons. These 3D polygons can be specified in terms of shape files (e.g. along coastlines, lakes, rivers, etc.), where each polygon vertex also has an attached height value (z coordinate). During the DSM's interpolation stage and/or Cloud Filter processes the specified polygons will be applied to either the raw DSM's or the raw Dense Clouds on-the-fly, leading to enhanced 2.5D and 3D surface models. Note that the raw DSM's and dense clouds themselves will remain unaltered by this process.

Follow these easy steps to enhance your surface models by applying water body polygons:

Step 1 - digitize waterbody polygons

In case shape files containing 3D polygons in the required format are already existing you can skip this step and directly move on to step 2. Otherwise, in order to digitize the 3D polygons, use any available data source, e.g.

  • digital terrain models (DTM)
  • LiDAR data
  • DSM or True Ortho data from previous projects

and capture the polygons along coastlines, lakes, and river shores using your preferred GIS.

If no data is available in order to digitize the polygons, proceed as following

  1. Setup your project with SURE as usual, disregarding the waterbody polygons. See also this article for further information.
  2. Process your project up until the DSM stage is finished.
  3. Use the produced DSMs (32 Bit TIFFs, representing height) or optional Orthos (colorized TIFFs) in order to digitize the required waterbody polygons. Additional QA layers which can optionally be produced by SURE can be beneficial for the digitizing process, for example the binary mask.
  4. Continue with step 2 and use either the 2.5D Tool or the command line Modules to generate the enhanced surface models and True Orthos

Shape file coordinate system

In order to be able to use the 3D polygons defined within the shape files in your project, make sure the shape files are defined in the exact same coordinate system than used throughout your SURE project. See also the related article about WKT format specification.

Single shape file

You can only specify one shape file (.shp) that contains all relevant polygons for your entire project. This shape file, however, can contain multiple polygons within a single layer.

Digitizing waterbody polygons with QGIS (3D Polygons supported since QGIS v3)

Step 2 - apply waterbody polygons

Either you already processed the dense clouds in the previous step 1 or you're setting up the project from scratch, you can use both the graphical user interface (GUI) or the command line interface (CLI) to apply the waterbody polygons defined in a shape file.

... using the GUI

If you're setting up a SURE project from scratch (Analysis and Dense Cloud yet to be processed) and a shape file containing water polygons is already available, specify the path to the shape file among the General Parameters during project configuration.

If the dense clouds and/or DSMs have been processed already, either reset & reprocess the DSM stage or use the 2.5D Tool to reprocess the existing data together with the polygons:

  • If available, open your existing SURE project in the GUI.
  • From the program's menu bar, choose "Tools" > "2.5D Tool"
  • Apart from specifying the waterbody shape file, adjust parametrization as required, e.g. specify
    • ground sampling distance (GSD)
    • tile size
    • area (ROI)
  • In case you're processing already rasterized DSM clouds, additionally
    • turn off the speckle filtering for the 2.5D workflow by setting it's radius to zero pixels.
    • reduce number of detections per cell among the 2.5D workflow parameters to one
... using the CLI

If shape files containing the waterbodies are already available, use SURE's command line interface like this:

  • SURE.exe -img ... -ori ... -scenario ... -waterbody <path-to-shape-file>

Otherwise, if you need to produce data in order to digitize the polygons still, first process the DSM stage separately, e.g. like this:

  • SURE.exe -img ... -ori ... -scenario ... -dsm -no_true_ortho -no_filter -no_mesh -no_meshtexturing

and use the standalone modules to apply the digitized polygons to the already existing DSM's:

  • ModuleDsm.exe --cloud <path-to-DSM-Cloud-folder> --waterbody <path-to-shape-file>
  • ModuleCloudFilter.exe --waterbody <path-to-shape-file>

Affected results

During the 2.5D workflow (DSM, True Ortho, DSM Mesh), the waterbody polygons will be applied to the raw DSM's on-the-fly, so the raw DSM's themselves will remain unaltered by this process. These outputs within the DSM subfolder will not be affected:

  • ProjectDirectory\DSM\DSM
  • ProjectDirectory\DSM\Ortho
  • ProjectDirectory\DSM\Cloud

When processing 3D workflows, the waterbody polygons will be applied to the raw dense clouds on-the-fly. The raw dense clouds themselves will not be affected:

  • ProjectDirectory\3D_Points

GUI interface