htrdr is free software. Far from a simple credo, the user is invited to study, modify and redistribute it according to his own needs. This page lists some of these forks developed by the htrdr community.

htrdr Urban

Fig. 1 - Rendering in the visible part of the solar spectrum of a procedurally generated dense mid-rise city. The number of pixels is 1500x800, the vertical field of view 70°, and the number of samples per pixel 200.

The htrdr Urban program is a fork of htrdr 0.6.1 that simulates radiative transfer in scenes composed of an atmospheric gas mixture, clouds, and a ground with buildings and vegetation. In addition of visible or infrared rendering of virtual scenes and calculation of solar or infrared irradiation, htrdr Urban adds the calculation of radiative flux density incident on or absorbed by a group of triangles belonging to the ground geometry (e.g. building, walls, windows, roofs, etc.) and humans. Visit the project repository for more information about this modification (features, installation process, use case, etc).

The following figures illustrate some of the results obtained with htrdr Urban.

Fig. 2 - Solar radiation budget of infinitely-long street canyon geometries with different aspect ratios (building height divided by street width) simulated with htrdr-urban (MC) and the Town Energy Balance (TEB), which calculates radiative exchange with the radiosity method. The radiation budget consists of the reflected radiation (UP) and the radiation absorbed by the roof (ABS_ROOF), walls (ABS_WALL), and road (ABS_ROAD). All terms have been normalized with the downwelling solar radiation. The plane area building density is 0.5. All surfaces have a Lambertian broadband albedo of 0.5. (left) The downwelling solar radiation consists of only direct radiation. (right) The downwelling solar radiation consists of isotropic diffusive radiation.
Fig. 3 - (left) Spatial distribution (1 m resolution) of the Mean Radiant Temperature (MRT) in a compact mid-rise urban district of 800 m x 800 m horizontal extent during the daytime. A rendering of the district is shown in Fig. 1. The solar elevation angle is 50° and the sky is clear. The sun is located in the west of the district (it shines from left to right) leading to low MRT due to shading on the right of the buildings and high MRT due to reflected solar radiation on the left of the buildings. The temperature of all surfaces is 295 K. The white colour depicts the built areas for which the outdoor MRT is not defined. (right) Standard deviation of the MRT displayed in (left) calculated by the Monte-Carlo method.