How to Use WebODM | Orthophoto Map

In the first article, we discussed the interface of WebODM and how to create and run a project. Here, let us understand the different types of outputs and tools available on WebODM. Using these tools, we will be able to change the properties of an orthophoto map and make accurate land measurements.

Table of Contents

1. Viewing an Orthophoto Map
   1. Layers
   2. Base Maps
   3. Importing a GeoJSON File
   4. Contours
   5. Measurement Tool
2. Plant Health
3. Digital Surface Model (DSM)

Viewing an Orthophoto Map

You can view your orthophoto map once it has been processed. Once the processing is completed, select the project and then select the task. You will see 4 options available under the completed task. Select ‘View Map’ (highlighted in red below).

Once you click on View Map, a 2D map of your photographed site will open with multiple tools and outputs.

The current selection is an Orthophoto output. You can also view the Surface Model (DSM) and Plant Health of the region. There are 7 tools that can be found on the right-hand side of the map. These consist of Layers, Base Maps, Importing a GeoJSON file, Measurements, Contours, Change Detection, and Elevation Map. At the bottom, you will also see an option to share this map and view it as a textured 3D model. But first, let’s look at all the features of the 2D orthophoto map.

Layers

    

This icon indicates the layers panel. Using layers you can change the following options:

1. View the points where the images were captured by the drone.
2. Show or hide the orthophoto layer on the base map.
3. Change the color settings of the orthophoto such as hue and saturation, sharpness, highlights, and shadows.
4. Exporting the orthophoto in .TIF format.

Base Maps

Base Maps is a useful tool to get the context of the surrounding areas. You can select up to 4 different base maps to place underneath your orthophoto. These maps are only used for reference and you can choose to omit them altogether. WebODM give the following selections:

1. Google Maps Hybrid
2. ESRI Satelite
3. OSM (Open Street Map) Mapnik
4. Custom
5. None

Note: To upload custom maps, you need to follow the tile URL template. The custom URL should be entered in the format shown below:

Importing a GeoJSON file

This option is used to import measurements, contours, and any data that is in the .JSON format. Once imported, the data can be placed over the orthophoto. Thus, using this feature you can import previous measurements saved on your desktop or data created by another user.

Contours 

Contours is a very useful topographical feature that can help in understanding the elevation of a landmass. The contour of an area is calculated using the Digital Surface Model (DSM) that WebODM generates by default.

When the preview is selected, yellow lines appear across the orthophoto. Lines that are separated signify elevated land and those that are merged together show flat land. You can change the contour settings to make the lines smoother, change the elevation interval between two lines, and even change the projection type. Finally, the contour overlay can be exported in 4 formats:

1. Geo Pakackage (.GPKG)
2. AutoCAD (.DXF)
3. GeoJSON (.JSON)
4. ShapeFile (.SHP)

Measurements

The Measurement tool is a crucial tool that can calculate the area, perimeter, volume, and path distance of a drawn path. You also have the option to export the measurements that you create. The measurement tool is easy to use.

To calculate a path distance, select ‘Create a new measurement’ and draw a line path across the orthophoto. If you wish to measure the area of a particular region in the orthophoto, draw a path around that area, joining the first and last points. Then click on finish measurement. This creates a closed shape and WebODM then calculates the area as well as the volume of that selected region.

The last two tools are used only in accordance with a Digital Terrain Model (DTM). Since WebODM does not create a DTM by default, we will explore the Change Detection and Elevation Map tools in another article. However, the tools discussed here are the fundamental tools required to analyze and calculate the different aspects of an orthophoto.

Plant Health

Plant Health is an added output offered by WebODM. In the Plant Health output, WebODM analyzes the vegetation of a region using algorithms such as NDVI, VARI, GNDVI, etc. This output can be useful in an agricultural site inspection or forestry. By clicking on the Plant Health model on the top, the orthophoto changes into shades of green, yellow, and red. The algorithm calculates the visible green light captured by the drone’s camera sensor. The red, orange, and yellow areas indicate diminishing plant health, whereas green shows healthy vegetation. In the example shown below, the plant health model is of an asphalt site and thus has little to no vegetation which can be inferred from the dominant shades of red and yellow.

Digital Surface Model (DSM)

The Digital Surface Model (DSM) or Surface Model, is a useful output that displays the elevation of the surface and all objects built on it. It can be used to detect faults and remote elevations along the surface or calculate the elevation of buildings or structures. The Surface Model shows the elevation in color codes ranging from blue (lowest point) to red (highest point). However, these color sets can be changed. 

In the next article, we will look at how to create a textured 3D model, analyze point clouds, and measure the created 3D mesh using various tools.

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