During analysis stage a project will be processed at an initially low pyramid level, i.e. for scaled down input images. The information gathered during this stage will be used to automatically determine various parameters, for example the GSD, the Area, or the most suitable stereo models for the dense matching.The project analysis comprises mainly four steps: (1) project generation, (2) image preparation, (3) initial level processing, and (4) stereo model selection.
During this first stage, the specified images and orientation data will be analyzed. The orientations will be matched to the corresponding images and stored in the SURE specific ORI format.
After finishing the project generation stage, the necessary image pyramids will be created. The initial pyramid level (usually 5 or 6 for large frame aerial imagery) will be determined depending on the actual size (rows/cols) of the input images. Within the project folder the image pyramids can be found in the folder "ImgMatch" for the match images, and "ImgTexture" for the texture images. The subfolders relate to the respective levels.
Pyramid creation mandatory
SURE expects the image pyramids to be created according to a specific standard. Due to the fact that there are various different definitions for actually creating the pyramids, SURE will discard any provided image pyramids and always create the pyramids according to our standard.
During the image preparation stage, while creating the image pyramids, also any distortion parameters specified in the orientation files will be applied to the images. SURE expects undistorted imagery for all subsequent processing steps.
Level 0 pyramids for distorted input images
Only if the specified input images have to be undistorted still, you'll find the level zero image pyramids, corresponding to the original resolution, within the "Level_0" folders for the texture images. Otherwise, the input images will be read from their original location specified while processing, thereby saving disk space to additionally store them unaltered within the Level_0 folders.
Initial level processing
During this stage, an initial set of matching candidates for each base image will be processed, i.e. matched and triangulated, on the initial pyramid level. From the results gathered here, further conclusions about the GSD, the Area (bounding box), and the most suitable stereo models can be drawn.
Stereo model selection
The next stage, the stereo models per base image will be determined.
For irregular image acquisition patterns (e.g. for close range) and for UAV projects, i.e. for "Scenario Default", the stereo model selection will be mainly based on
- the minimal matched image fraction, determined during initial level processing of the set of matching candidates,
- the maximum number of stereo models per base image, and
- the minimum/maximum principal angle, derived from the given orientations.
For regular flight patterns (e.g. large frame airborne acquisition), by specifying a corresponding scenario, i.e. "Scenario Aerial Nadir" or "Scenario Aerial Oblique", an additional block analysis procedure will automatically identify flight strips and oblique view groups, and utilize this information for stereo model selection.
After setting up your project with SURE, e.g. using the software's Project Wizard, don't run the complete pipeline at once. Instead, process only the Analysis stage, either by pressing the small play button next to the Analysis stage in the GUI, or by passing the '-analyze' flag on the command line. Afterwards, review the automatically determined values like the GSD, tile size, area, and adjust them if required. Also review the selected stereo models in the GUI's Camera Stations view. This approach is especially recommended if you don't know how to best configure your project.
Color adjustment parameters calculation
As a next step during Analysis the calculation of the parameters needed for color balancing is implemented. These parameters are stored in the colorAdjustmentFile.txt, located in the project folder. The color adjustment parameters are calculated when the initialization cloud from the Init folder is ready.
By default the colorAdjustmentFile will be calculated. If the user does not want to color balance the output TrueOrtho/2.5Mesh & 3DMesh. Then in the CLI the flag of '-no_color_adjustment' can be specified. We would recommend to run the Analysis with -color_adjustment. If later in the process you decide that you do not want a color adjustment for the TrueOrtho/Mesh then you can directly specify in the modules the flag of -no_color_adjustment.
Else the user has to rerun the Analysis in order to obtain the colorAdjustmentFile.txt
GUI: Color Adjustment
In the GUI the option of Calculate Color Adjustments is active by default. In case there is an Area shape file imported the color adjustment will be calculated only for the imagery that falls in that area. It would be recommend to calculate the color adjustment for the entire bloc. The option of Apply Color Adjustments relates to the user needs of having or not a color adjusted TrueOrtho/ Mesh. If active the ColorAdjustmentFile.txt will be automatically used in the process of producing a color corrected True Orthophoto/ Mesh.
In the GUI the option of Custom Color Adjustments is needed in special situations. Assuming that the color adjustment was processed for the entire dataset, this option will allow the user to have for a smaller area of interest, a product with similar color adjustment as the dataset. For example, if the user would like to generate a smaller area of True Ortho/Mesh that has similar color adjustments with the entire dataset.
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