In the last article, we learned how to create an orthophoto map, digital surface model, monitor plant health, and use the various tools available. Here, we will look at a 3D point cloud and textured model. A point cloud is a set of data points in space. Each data point has an x, y, and z coordinate. So, this facilitates in creating accurate measurements, determining the height of structures, volume, etc.
Viewing a 3D Point Cloud
To view the point cloud of a completed task select the completed task. Five options appear below the completed task. Select the ‘View 3D Model’ option (highlighted in red below).
The selection will open a 3D point cloud of the map. This is the interface of the 3D view of your map. If you zoom in, you will see that this 3D view comprises individual data points floating space. Each of these data points has an x, y, and z coordinates. Measurements are calculated using the distance, area, altitude, etc. of the selected points.
There are several tabs available on the left-hand side: Cameras, Textured Model, Appearance, Tools, Scenes, and Filters. Let’s look at some tabs that will be useful to make measurements and modify additional settings.
Under the Tools tab, there are 3 sub-panels: Measurement, Clipping, and Navigation.
The measurement panel consists of the most important tools that provide the most utility. These tools can help in calculating angles, slopes, altitudes, etc. Let’s go through some fundamental measurement tools:
Angle Measurement Tool
The Angle Measurement Tool is primarily used to calculate the angle between two structures, buildings, etc. or any arbitrary angle on the point cloud. To begin, select the tool. A redpoint appears at the cursor. This is the axis point, place this at the point from where you need to calculate the angle. Then, drop the last two points based on the extent of the angle and distance. Angular measurement at each point will be displayed.
Point Measurement Tool
Point Measurement is a relatively simple tool whose function is to display the x, y, and z coordinate of a single point. X,y denotes coordinates of a point in WGS84 UTM format, while z denotes height based on WGS84 ellipsoid. This tool can be used to determine the highest or lowest point on a structure or on the terrain.
Distance Measurement Tool
The Distance Measurement tool is used to measure the distance between two or more points. This can be helpful in determining the perimeter of a structure or a path distance. If you draw a single path, the total distance is displayed. However to calculate the total distance, in the case of multiple paths or a perimeter, scroll down to the Scene tab and then further to the Properties panel. There, you will be able to view the total path distance. We will discuss the Scene tab in detail but to check x, y, and z coordinates or the total distance, volume, etc., scroll down to the properties panel under the Scene tab.
Height Measurement Tool
This tool calculates the height of a particular structure. You can either calculate the height of a small portion or an entire structure depending on where you place the base point. To begin, place the first point at the lowest level, and the second at the highest. The vertical height between the two points will then be displayed.
Circle Measurement Tool
The Circle Measurement tool draws a circle over a section of a map. Using the circle’s properties such as circumference and radius, you can measure the same on the map. The measurements are displayed at the properties panel under the Scene tab.
Area Measurement Tool
This tool measures the area of a drawn shape. This can be helpful in land management, stockpile management, etc. To begin, just place points on the perimeter of a region whose area you want to calculate. When finished plotting the points, right-click to finish the process. The area is then displayed at the center of the figure.
Volume Measurement Tools
There are two volumetric tools available for symmetrical volume measurement in a point cloud: The cuboid and sphere. Using these two tools you can calculate the volume of symmetrical structures like buildings, vehicular loads, stock on a construction site, etc. To use the tools, select either one depending on the form of the structure, and left-click on the point cloud. This will place a cuboid or a sphere on the point cloud.
The volumetric shape will have 4 control handles to alter the dimensions of the 3D shape. Also, it has 4 arcs to control the rotation, height, and width of the shape. Using the handles and arcs, position the 3D shape over your structure accurately. Once positioned, scroll down to the properties panel, the total volume (cubic meter) will be displayed.
Height Profile Tool
The Height Profile tool is used to calculate the change in elevation between two points. Similar to the height measurement tool, it not only provides the vertical height but calculates the different elevation points along the path. To create a height profile of a slope or uneven land, select the height profile tool and mark two points.
The change of elevation between them is denoted by a band. You can increase or decrease the number of points (change the width) allocated in that band. To modify the width of the elevation band and view the height profile, scroll down to the properties panel under the Scene tab. Here, you can manually enter a numeric value to modify the width. To view the height profile select the ‘show 2D profile’ option.
A height profile graph opens with z value of pixels on the y-axis and the distance in meters (change in z) on the x-axis. On the top left corner, the total number of data points between the two height profile points is given. In the above-shown example, the total number of data points is 11,722. Thus, by moving the cursor over the plotted points, you can view individual x, y, and z values of each point. Therefore, through this graph, you will be able to measure the change in elevation. On the top right corner, there is also an option to export this graph as a CSV (2D) or LAS (3D) file.
Lastly, there is an annotation tool to label objects and a clear tool to clear all measurements from the map.
The tools under the clipping panel are used to crop the map into various shapes. You can clip the map to isolate a segment and measure it more accurately. There are three basic types of clipping tools available:
- Volume Clip: This tool crops out 3D shapes from the map.
- Polygon Clip: Using this tool, you can create a polygon area and crop/highlight it.
- Section Clip: This tool works in accordance with the orthographic camera view and crops boxed sections.
The Navigation panel is used to maneuver the 3D map. Using navigational tools, you can change the angle of view, perspective, zoom distance, rotation, and orbit. There are 8 tools in the navigation panel out of which 6 are used to change viewing angles. The remaining two: Compass and Camera Animation have different functions.
Selecting the compass, a small compass will appear on the map to facilitate in directions. The Camera Animation tool on the other hand helps in creating a frame by frame video animation of the map. You can position several points across the map and the camera will cruise through those points, creating an animated tour of the map. You can then download the animation.
The Scene tab is similar to the layers tab in an orthophoto map. Here, you can view all the ‘layers’ of measurements and overlays on the point cloud under the objects panel. You can choose to hide the overlays. Additionally, all the measurements and overlays can be exported into JSON, DXF, or Potree formats.
Further scrolling down, there is a properties panel wherein you can view the total area, volume, and distance measurements.
The Cameras tab has a simple function of visually creating the various positions of the drone from where the images were captured.
The Appearance tab comprises the tools that refine the point cloud. You can increase or decrease the total number of points on the map and also the field of view. Additionally, you have the option to change the lighting scheme and modify background overlays. In the ‘other’ panel you can modify the minimum node size, which will essentially modify the size of each individual point.
Lastly, you can stitch up all the data points together to form a seamless textured 3D mesh under the Textured Model tab. The 3D mesh will be fully texturized and can be exported for presentation. You can open the .OBJ file of the model in software like Blender, Mesh Lab, etc.
In the next article, we will look at the administrative settings of WebODM, changing appearance, presets, plugins, and much more.
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