The hard part was obtaining information such as solar azimuth, altitude, declination, hour angle, etc without using external APIs. Spent around 5 days implementing backend.
Way too late now, but to help others this fancy Excel sheet provided by NOAA is awesome! It implements all of these equations in Excel and is pretty easily portable to your programming language of choice. https://gml.noaa.gov/grad/solcalc/calcdetails.html
P.S. Using this has made it clear to me how bad most sunrise/sunset calculators actually are.
> P.S. Using this has made it clear to me how bad most sunrise/sunset calculators actually are.
That may just be a function of how you define "sunrise" and "sunset". It is never as simple as "when the sun hits the horizon", but something about some number of arc minutes from something something.
Dependent on the refractive index, which depends on air density and temperature and humidity too; and we have to integrate over the region between the horizon and the upper atmosphere (diagonally, of course)…
To be clear I was complaining that basically everyone calculates “sunrise” and “sunset” differently. If you check half a dozen different “sunset” calculators you will get a surprisingly wide variation in the times they provide. At least where I live the error seems to average 5-10 minutes.
I'm not sure what you mean by external APIs but is there a reason you're not using SunCalc[1] on the client to process the route after it's returned from the routing engine?
P.S. Using this has made it clear to me how bad most sunrise/sunset calculators actually are.