The manual classification processes in PCS can be used to correct classification errors or convert a dataset for different types of use, for example, creating a sample dataset for machine learning scenarios, where a specific kind of object shall be trained for an ML engine from the point clouds.
Before reading this article, please make sure you are familiar with the Classification concepts reading the respective article. It is highly recommended that you get familiar with the clip frame toolbar and its mechanics. This article does not refer to vectors. It is not mandatory to read the Basic or Advanced extraction guide. The user is also not required to read the Semi-Automatic Classification guide.
IMPORTANT! - The classification can be initiated only on LAS files; all points are loaded to the memory, as described in the optimizing article. A minimum of one LAS file shall have all points in memory; otherwise, the classification toolbars remain inactive. Also, it is impossible to load more GB of point clouds with all points in memory to the software than physical RAM installed on the PC.
The manual tools in PCS are based on a planar approach, which means that only planar views are sufficient for reclassifying something with the manual method. This means the 2D or the 3D view using the profile mode from the Clip Frame toolbar. PCS offers two primary types of manual reclassification tools: the polygon toolkit and the brush.
As the name suggests, the polygon toolkit can fence polygons in 2D or 3D view - when the profile mode is active - and the fenced area, or below or above the selected line, will be reclassified. This rougher tool allows the user to reclassify bigger chunks of the point cloud. Polygon toolkit can be found in the Main Classification toolbar and the 3D view Classification toolbar.
Using the 3D view classification toolbar, as with the polygon tool in 2D view, will reclassify everything in the marked area and not consider the elevation, except the classification settings have not been set specially for this.
The other tool is the brush. It also requires the profile mode for the 3D view. The brush does allow the user to perform a fine classification by hand. After the tool has been started, the user can set the source-target classes, set the pixel size, and turn on track mode (which is recommended). This will allow the user to draw - like using the brush in paint - and reclassify for the “painted” area.
The best practice for classification tasks for manual processes is to crosscheck the object from 2 sides, for example, front and left. Swapping the sides of the clip-frame tool from the Clip Frame toolbar can be handy for this task, as the perpendicular crosscheck can eliminate most of the manual classification errors.
After the classification has been performed, always save the modified point cloud. If it is not saved, the save warning will also prompt the LAS files for saving, but right-clicking on the Clouds inside the Project Explorer and selecting save is also a good approach.