Metashape Professional edition supports processing of the data captured by thermal cameras and saved in R-JPEG (FLIR data) format. The article describes the basic stages of R-JPEG data processing.
Loading photos
For R-JPEG data it is required that the images are loaded in Metashape using multi-camera system layout option. To load images follow the steps below:
1. Add thermal images to the project using Add Folder... command from the Workflow menu.
2. In Add Folder dialog box browse to the parent folder containing subfolders with images. Then click Select Folder button. And choose Multi-camera system in Add Photos dialog:
3. Click the OK button to close the dialog.
Check that the images are added as multi-camera system, i.e. in Tools > Camera calibration window there should be two separate cameras: one RGB and one Thermal:
It is recommend to fix the focal length in the Camera Calibration dialog:
Aligning photos
The next stage of the data processing is image alignment. It includes the following steps:
1. Select Workflow > Align Photos.
2. In the Align Photos dialog window set preferable parameters.
The alignment results comprise estimated external (camera position + orientation) and internal parameters as well as the tie point cloud (visualization of triangulation for matched feature points procedure). The results are displayed in the Model view:
Building DEM
Digital Elevation Model (DEM) represents a surface model as a regular grid of height values. DEM can be generated from one of the following spatial model representations: tie points, depth maps, point cloud or mesh. DEM is calculated for the part of the model within the bounding box. In the example project the depth maps were used for building DEM.
1. Select Build DEM... command from the Workflow menu.
2. In the Build DEM dialog window set the preferable parameters.
3. Click OK button. The progress dialog box will appear displaying the current processing status. To cancel processing click Cancel button.
Building Orthomosaic
To build an orthomosaic there should be a surface where the images will be projected to. In the described project the DEM had been used as a Surface.
1. Select the Build Orthomosaic... command from the Workflow menu.
2. Set parameters in the Orthomosaic dialog window.
3. Click OK button. The progress dialog box will appear displaying the current processing status. To cancel processing click Cancel button.
Temperature values visualization
To extract the absolute temperature values from the thermal orthomosaic it is necessary to define the formula that would transform raw values to the temperature values via Raster Calculator dialog window.
To obtain temperatures, a sensor that is able to provide absolute temperature is needed (instead of relative temperature). The FLIR Vue Pro and the Zenmuse XT do not provide absolute temperature values. However both cameras have a radiometric version that does record absolute temperature.
The following formula to calculate absolute temperature values:
0.04*thermal_ir - 273.15
Select Set Raster Transform command from the Tools menu. Add the formula in the Transform tab:
Once the transformation is completed the temperature will be shown in the lower-right corner of the Ortho view as the Index value for the area pointed by the cursor.
