User story: This is how survey engineer Nils Lindqvist slims the point cloud
The point cloud is incredibly rich in information. But all data is not needed and therefore the point cloud must be filtered. Here, Nils Lindqvist at Lindqvist Mät AB, shares his best tips for ease of handling.
A great portion of experience. That is an asset for survey engineer Nils Lindqvist at Lindqvist Mät AB in the process of transferring the landscape in front of him to a manageable model in the computer. First, he lets his eyes sweep over every part of the terrain, wandering around and studying what it really looks like. A solid ocular inspection where every pit, gravel pile, hill or other formation is noted. Why?
– To be sure that the point cloud portrays the landscape more fairly, Nils explains.
He benefits from Topocad when the points are to be processed. The software is given companion in the projects and has been so, since 2005.
From drone to point cloud
After the inspection, Nils starts the work by letting a drone fly over the area. With the help of photogrammetry, the aerial photo is transferred to a point cloud which he then processes in Topocad, where it’s colorized. He usually uses the point cloud to develop terrain models, but he also does volume calculations.
In order for the point cloud to get the right position, he has placed plates marked with X in the terrain, which are later measured with a GPS. Then the drone flight is georeferenced and thereby all the points in the cloud. In addition, he has developed his own methodology to ensure that the result is as correct as possible.
– I measure some points that I compare with the point cloud, so it has the correct geoposition. It is a way for me to assure the quality of my work, so that the point cloud matches reality.
The measured points are solely for himself and are not reported in the project.
A point cloud is incomparable rich because the drone has, without discernment, portrayed what has come in its way. But everything is not relevant. Trees, bushes, a bunch of birds and other irrelevant objects must therefore be eliminated, so that the point cloud gets the required quality.
Thanks to the colorful point cloud in Topocad, Nils can easily identify the objects that have no place in the project and should be removed. He has not yet tested the new feature for identifying trees in the point cloud, launched in Topocad version 1.2, but will soon do so.
Filtering is also done to make the points easier to handle. But, Nils emphasizes, it must not be sacrificed for the content quality of the point cloud. It must be intact in order to not jeopardize the result.
Here are some of his tips for generalizing the data set using Topocad.
Tip! Filtration in flat surfaces
When the terrain consists of flat surfaces, Nils adds a grid in the point cloud that has fixed dimensions, for example two times two meters, which determines a fixed point density in Topocad. However, it depends on what the surface looks like, of course. The flatter the surface, the greater the distance between the points in the grid, and the points that fall out are removed by the software. The method reduces the number of points in the grid.
Tip! Filtration in hilly areas
However, if the terrain varies with different elevation differences, Nils works in another way. With the help of the point cloud he creates altitude curves with maintained point density. Then he pastes the raster image of the orthophoto and when, for instance, a trees height curves are included, Nils can remove it in Topocad.
Tip! Benefits from Lantmäteriet’s grid models
Another tip that Nils shares is the use of grid models from Lantmäteriet. They scan using a drone, and produce point clouds that are formed into grid models in two times two meters. The cloud contains points that are in the soil layer and all trees and other vegetation have been removed.
– You can work with Topocad in many ways, Nils tells us. This is how I prefer to work, it’s very productive for me and my projects.
This shows how flexible the software is. The point cloud gets easier to work with thanks to the software. Time is freed, which would rather be spent on new projects with the drone.
By: Love Janson
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