Convert a point cloud into a digital surface (or terrain) model with colors.
Project description
Overview
cars-rasterize aims to convert a point cloud into a digital surface (or terrain) model with colors.
It is a part of the photogrammetry tool cars extracting Digital Surface Models from satellite images.
Installation
cars-rasterize is available on Pypi and can be installed by:
pip install cars-rasterize
Quick start
- Download subsampled_nimes.laz*:
wget https://raw.githubusercontent.com/CNES/cars-rasterize/master/data/subsampled_nimes.laz
subsampled_nimes.laz |
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subsampled_nimes.laz* is from https://geoservices.ign.fr/lidarhd. and has been downsampled (1 point every 50cm) to make the file smaller.
- Run las2tif executable:
las2tif subsampled_nimes.laz dsm.tif --clr_out clr.tif
- ✅ Done! The executable generates two files:
- dsm.tif: the elevation of the points (Z dimension) are projected into a regular grid to generate a raster file named Digital Surface Model.
- clr.tif: the red, the green and the blue dimensions can be also projected producing a color interpretation map superimposable on DSM
dsm.tif | clr.tif |
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How it works
A LAS file contains a set of points $P = {(x, y, z, r, g, b)_k}$ each having several dimensions:
- $x$ and $y$ correspond to planimetric information
- $z$ corresponds to the altitude
- $r$, $g$ and $b$ correspond to colorimetric information (respectively red, green, blue )
To create a raster digital surface model, we define a regular grid on a region of interest roi of origin $(x_{start}, y_{start})$, size $(x_{size}, y_{size})$ with a constant resolution.
For each cell of center $(c_x, c_y)$, we consider the subset of points contained in the disk $D$ (parameter radius) centered on this cell (see figure below):
Contributing points |
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Then, the altitude assigned $z(c_x, c_y)$ to the cell is a Gaussian weighted average (standard deviation sigma $\sigma$) of the distance $d$ to its center :
$$z(c_x, c_y) = \frac{\sum_{p_k \in D} z_k e^{-d_k^2/2\sigma^2}}{\sum_{p_k \in D} e^{-d_k^2/2\sigma^2}}$$
Finally, to have a superimposable color to this dsm, the colors are averaged in the same way.
Contribution
cars-rasterize is a free software: Apache Software License 2.0. See Contribution manual.
Project details
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