In this article, we will describe how to process data from Sentera 6X multispectral sensor.  We describe the main steps and the general recommendations for processing in Agisoft Metashape Professional.


This article describes the following processing steps:


Add photos

To add photos select Add Folder... command from the Workflow menu, select the folder containing the individual band folders. The images are grouped into folders of the corresponding channel. 



Note:

  •  Photos must be added as a multi-camera system to produce a multispectral mosaic.  
  •  The number of images per band folder must be the same. Otherwise, all of the bands will not be added to the chunk.



  • We recommend processing RGB images separately, without using them in the multicamera method. 

Camera Calibration settings

Photogrammetric calibration of cameras is performed to determine the values of the interior orientation of the cameras, including the parameters of distortion of the camera lens.  To open Camera Calibration dialog window, select Tools > Camera Calibration.


By default NIR is selected as the master band, the NIR images have the highest chance of becoming oversaturated in poor lighting conditions without a sun sensor so I always change the master band to Green by right-clicking the green band and clicking Set as Master.



By default the layer index for each band is set to  NIR: 0, Blue: 1, Green: 2, Red: 3, RedEdge: 4. You can set the layer index accordingly.  This can be chosen differently by the user since some users may rather have the bands ordered Blue, Green, Red, RedEdge, NIR. Open Bands tab on the Camera calibration dialog window and specify Layer index if you want to change layer order:



Metashape can perform automatic calibration during align photos step. If very precise calibration data is available, click Select... button next to Fixed parameters: item. In Fixed parameters dialog choose calibration parameters that are to be fixed and click OK button. The initial values for the chosen parameters will not be changed during Align Photos or Optimize Cameras operations. 



Align photos

Align photos and model/mesh generation is the same as the process for any other sensor and can be changed by the user depending on their needs. Select Align Photos... command from the Workflow menu.



Note:

  • it is advisable to use the Reference preselection - Source if there are coordinates of the photographing centers.


The result of the align photos operation will be shown in the Model view as the estimated camera locations and tie point cloud, representing the matching points between the images.



Build DEM

A DEM represents a surface model as a regular grid of height values. DEM can be rasterized from a dense point cloud, a sparse point cloud, depth maps, or a mesh.  If you need you can build a Dense cloud before starting build DEM. 


Note: 

  • If you need to build a dense point cloud (if you want to perform terrain classification later), you need to build a cloud with the following parameters: Medium quality, Mild filtering. After that, you can use the classified point cloud to build a DEM.
  • DEM is calculated for the part of the model within the bounding box.  


1. Select the Build DEM... command from the Workflow menu.


2. In the Build DEM dialog box set parameters. 




3. Click OK button. The progress dialog box will appear displaying the current processing status. To cancel processing click Cancel button.


Orthomosaic Generation


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.  


Note: 

  • Metashape enables the calculation of NDVI  and other vegetation indices based on the multispectral imagery input. The vegetation index formula can be set by the user, thus allowing for great flexibility in data analysis. Use Set Raster Transform option from the Tools menu to open Raster Calculator dialog. On the Transform tab specify the index values that you would like to calculate from the source data.