Tutorial #A2 : orthophoto generation
Orthophoto Generation Workflow
Welcome to the 3DF Zephyr tutorial series.
In this guide, you will learn how to generate and customize an orthophoto with 3DF Zephyr.
This tutorial cannot be completed with 3DF Zephyr Free or Lite versions!
Introduction
3DF Zephyr allows generating of true orthophotos from a mesh or creating orthomosaics from a sparse or dense cloud. To explore this topic further, you can check out this quote from Wikipedia:
An orthophoto (or orthomosaic) is a geometrically corrected (“orthorectified”) picture whose scale is uniform. The photo has the same lack of distortion as a map, and, unlike standard images with a certain level of perspective, an orthophoto allows measuring true distances.
You must create a (scaled and georeferenced) point cloud or mesh in your project before generating an orthophoto in 3DF Zephyr.
Summary
Step 1 – Setting the orthophoto’s source
You will notice different orthophoto generation options from the “Workflow” Menu:
- Orthophoto from sparse points (requires generating sparse points cloud).
- Orthophoto from dense points (requires generating dense points cloud).
- True Orthophoto from Mesh (requires generating the mesh).
By selecting the True Orthophoto from Mesh (1) option, the Orthophoto Wizard window (2) will open, and a Bounding box (3) appears in the 3D workspace.
On Step 1 – Orthophoto Source page, you can define the boundaries of the orthophoto by changing the dimensions of the bounding box in the workspace and also set the reference plane from another axis or at least 3 GCPs. It’s possible to select another Reference object (4) among the created meshes. The button Adapt bounding box allows changing the bounding box size of the mesh automatically.
The default settings of the Orthophoto Wizard will create an orthophoto of the whole 3D model with the reference plane on the Z axis; if this is the desired situation, press the “Next” button and proceed to Step 2 page.
Changing the orthophoto’s reference plane
The workflow below will allow setting the reference plane using GCPs for creating an orthophoto’s facade. While changing the reference plane or the image up direction, it will be possible to see a preview on the bounding box represented by the red text: 🠝THIS WAY UP🠝.
Note: it’s best to change the Reference Plane and Image Up directions first, as this will reset the bounding box size each time.
At least 3 control points must be placed before with the GCP placement tool: “From images” (available on the GCP panel) on the mesh to define the plane of the orthophoto.
Click on the “Reset reference plane from control points” (5) button to open the Define up vector with control points (6) window.
Select 3 or more control points (7) to define the orthophoto’s plane. As a preview during the GCP’s placement, a yellow line (8) will represent the normal’s direction in the workspace.
After clicking the “Ok” button, the GCP’s plane normal will become the new world-up vector.
We can also use the “Select image up from axis” (9) function to choose the axis for orienting the orthophoto’s image up direction.
The red text: 🠝THIS WAY UP🠝 (10) will preview the new plane orientation on the bounding box.
The orthophoto borders can be decided by Setting the bounding box in the viewport (11) or changing the parameters in the Extents and Euler Angles sections. Through the checkboxes, it is possible to restrict one or more axes on which to move or rotate the Bounding Box.
Once the source of the orthophoto has been set, you can continue with the “Next” button.
Step 2 – Choosing the orthophoto resolution
The Step 2 – Resolution page of the orthophoto wizard will present a set of options to define the orthophoto resolution by changing the Ground sample distance (GSD), specifying the image size, and Generation parameters for controlling pixel’s colors. The Camera to use section allows the choice to ignore cameras during the generation process by cameras directly or by tags.
The orthophoto Width and Height can be adjusted according to the desired Ground Sample Distance (1), or you can set the GSD directly and let 3DF Zephyr calculate the resolution for you. The workspace will show a preview, while the green rubber band (2) will define boundaries within the orthophoto image.
The Step 3 page will be available by pressing the “Next” button.
Note: The 3Dflow Ground sampling distance calculator can be used to find the best GSD in relation to the resolution of your images.
Follow this link to use the calculator: https://www.3dflow.net/ground-sampling-distance-calculator/
Step 3 – Export the orthophoto
This section allows choosing the export settings and additional deliverables for the orthophoto.
In the Export (1) drop-down menu is possible to choose to export only the orthophoto, the DSM, or both.
The Image format (2)drop-down menu allows you to save the Orthophoto in these image formats: *.jpg, *.png, and *.tif.
Optionally, the Export DTM (Digital Terrain Model) checkbox can be checked depending on the scene type. Three scenarios are available: (Mountain area, Complex scene, and Flat terrain).
In the Extra section, you can add additional files to export by selecting the following checkboxes:
- – Export Pdf file: exports the orthophoto in Pdf format.
– Export KML file: by enabling this checkbox, you can export an orthophoto in KML format for Google Earth.
– Export Autocad script file: by enabling this checkbox, you can export a .scr file that can be automatically dragged into the Autocad workspace and will allow exporting the orthophoto with the correct scale set in 3DF Zephyr.
– Export World file: exports the World file.
When everything is ready, click “Finish” (3), and select the file name and destination folder (4). A preview (5) of the exported files will be shown in the Save As window. Press the “OK” button to launch the orthophoto generation.
The orthophoto will be available in the right Project panel and saved on your computer.
Note: Zephyr will automatically open its DEM Viewer utility when the process is complete, and will be possible to view the orthophoto, and DSM overlaid.
Final notes
In the Verruca Fortress case study; you can see an example of how the orthophotos created in 3DF Zephyr can be used in an applied scenario.
