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Using rgl's extrude3d() function to make a 3D mesh from polygons in R

2 min read 29-08-2024
Using rgl's extrude3d() function to make a 3D mesh from polygons in R


Creating 3D Meshes from Polygons in R using rgl::extrude3d()

This article explores the power of rgl::extrude3d() function for transforming 2D polygons into 3D meshes in R. We'll use a real-world example of extruding polygons representing areas with varying attributes to create a visually impactful 3D representation.

Background

Creating 3D models from geographical data often involves converting 2D polygons into 3D surfaces. This is particularly useful for visualizing spatial data with varying attributes, such as population density, elevation, or pollution levels. The extrude3d() function within the rgl package offers a convenient and powerful method to achieve this transformation.

The Problem

Imagine you have a geopackage containing multiple polygons, each representing a distinct area. Each polygon has an attribute called "POINT...50" which represents the desired height of the extruded 3D object. We need to use this attribute to control the extrusion height for each polygon, resulting in a 3D mesh with varying heights.

Solution

The rgl::extrude3d() function is designed to transform a set of polygons into a 3D mesh. We'll leverage this function and combine it with other functionalities to achieve our goal:

  1. Read the Data: We begin by reading the geopackage using the sf package.
  2. Extract Height Values: We extract the values of the "POINT...50" attribute from the polygon data.
  3. Extrude Polygons: We use extrude3d() to create 3D meshes from the polygons, using the extracted height values to determine the extrusion depth.
  4. Visualize and Export: We visualize the 3D mesh using rgl::plot3d() and export it as an OBJ file for further use.

Code Implementation

library(sf)
library(ggplot2)
library(rgl)
library(dplyr)

# Load data
data <- st_read("data/métropole_de_lyon_LGT_LCI_500m.gpkg")

# Extract height values from "POINT...50" attribute
heights <- data

   


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Using rgl's extrude3d() function to make a 3D mesh from polygons in R

                                                

                                                   

                                                      

                                                         

                                                            
                                                            

                                                               

                                                                  
                                                               

                                                               

                                                                  
                                                                     

                                                                        
                                                                           

                                                                              2 min read
                                                                              
                                                                              29-08-2024
                                                                              
                                                                              
                                                                           

                                                                        
                                                                     

                                                                  
                                                               

                                                            

                                                         

                                                         
                                                      

                                                   

                                                

                                             

                                             

                                                

                                                   

                                                      
                                                         Using rgl's extrude3d() function to make a 3D mesh from polygons in R
                                                      
                                                   

                                                

                                             

                                             
 






 
                                             
POINT...50`

# Create 3D mesh using extrude3d()
data3D <- extrude3d(data, depth = heights)

# Visualize the 3D mesh
plot3d(data3D)

# Export the 3D mesh as an OBJ file
writeOBJ(data3D, '3d_model.obj')

Explanation

  • st_read(): This function from the sf package loads the geopackage into an sf object.
  • **data$POINT...50:** Accesses the values of the "POINT...50" attribute from the data` object.
  • extrude3d(data, depth = heights): The core of the transformation. The data argument provides the polygons to be extruded, and depth = heights defines the height for each polygon using the extracted heights values.
  • plot3d(data3D): Visualizes the resulting 3D mesh using rgl.
  • writeOBJ(data3D, '3d_model.obj'): Exports the 3D mesh to an OBJ file for external use, such as 3D printing or further processing.

Important Notes

  • The extrude3d() function expects a list of polygons as input. In our example, we assumed the geopackage contains multiple polygons.
  • The "POINT...50" attribute is specific to the example data. You may need to adjust the code based on the specific attribute names and data structure you're working with.

Adding Value Beyond Stack Overflow

While the Stack Overflow question addressed the basic functionality of extrude3d(), this article provides a comprehensive example with real-world data and explanations. This includes code comments, detailed steps, and context about the importance of creating 3D meshes from spatial data.

Conclusion

The rgl::extrude3d() function enables powerful 3D visualization capabilities in R, allowing for the conversion of 2D polygons into insightful 3D models. By leveraging this function and combining it with other packages like sf, we can create rich and informative visualizations from spatial data. The process can be further customized and extended to create complex 3D models with varying textures, colors, and even animations, depending on your specific needs.

r 3d rgl

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