Modeling sunpath on Mars

Benji · January 5, 2021, 6:40pm

Hi, new Ladybug user here (and fairly new to Grasshopper)!

For a university project I am designing PV panels for (future) habitats on Mars and I would like to model the sunpath there.

The way it’s modeled on Earth is fairly straightforward (albeit complex) right? The solar altitude depends on the geographical latitude, the time of day and the solar declination (depending on the day of the year, -23.45° < δ < +23.45°), represented by a nice sine function which should be the same for Earth and Mars.
The parameters based on time can be sort of ignored since we’d like to model the sunpath for a whole Martian year, the extreme declinations on Mars are known (-24.936° < δ < +24.936°), and the latitude is free to choose. The durations of a Martian day and year are also known using Earth units (sec/min/h).

So my question is, is there a way to alter these parameters inside Ladybug commands such that a proper model of a sunpath over a Martian year at any latitude on Mars can be made?

Any thoughts or tips in general are welcome!

Alakelele · November 28, 2021, 11:01pm

Were you able to modify the code yourself ? I would be interested in helping or sharing your research, I myself created a code for a human outpost on mars, look up Mars Base Rhino on this forum

chris · December 7, 2021, 9:10pm

You should be able to do this by only editing one module within Ladybug, which you can see here:

github.com

ladybug-tools/ladybug/blob/master/ladybug/sunpath.py

# coding=utf-8
"""Module for calculating sun positions and visualizing the sun path."""
from __future__ import division

from .location import Location
from .dt import DateTime
from .analysisperiod import AnalysisPeriod
from .compass import Compass

from ladybug_geometry.geometry3d.pointvector import Vector3D, Point3D
from ladybug_geometry.geometry3d.plane import Plane
from ladybug_geometry.geometry3d.arc import Arc3D
from ladybug_geometry.geometry3d.polyline import Polyline3D
from ladybug_geometry.geometry3d.line import LineSegment3D
from ladybug_geometry.geometry2d.pointvector import Point2D
from ladybug_geometry.geometry2d.polyline import Polyline2D

import datetime as py_datetime
import math
import sys

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On Windows, you will find this file here:

C:\Users\[USERNAME]\ladybug_tools\python\Lib\site-packages\ladybug\sunpath.py

Specifically, changing things in this calculate_sun_from_date_time method and the other hidden methods that it calls should effectively switch the whole Sunpath over to wherever you want in the solar system:

github.com

ladybug-tools/ladybug/blob/master/ladybug/sunpath.py#L235-L304

    
      
          def calculate_sun_from_date_time(self, datetime, is_solar_time=False):
              """Get Sun for a specific datetime.
          
          
    This code is originally written by Trygve Wastvedt (Trygve.Wastvedt@gmail.com)
              based on (NOAA) and modified by Chris Mackey and Mostapha Roudsari.
          
          
    Args:
                  datetime: Ladybug datetime.
                  is_solar_time: A boolean to indicate if the input hour is in solar
                      time. (Default: False)
          
          
    Returns:
                  A sun object for the input datetime.
              """
              # TODO(mostapha): This should be more generic and based on a method
              if datetime.year != 2016 and self.is_leap_year:
                  datetime = DateTime(datetime.month, datetime.day, datetime.hour,
                                      datetime.minute, True)
          
          
    # compute solar geometry

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Bear in mind that the Python datetime modules are still all going to be in Earth time so you may need to add some functions to convert between Earth datetimes and Mars ones.