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Posted by okh
at Aug 22, 2016, 9:19:32 AM
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Re: Is it rendered at AM or PM? (Why I'm struggling with the time of day.)
Hi Mike,
No need for guessing, getting it right is not difficult and once the compass is set with correct longtitude / latitude, orientation, time-zone (and date in the create photo dialogue), the sun rendering is very accurate. I seem to remember that even DST (Daylight Saving Time) is considered by the rendering engine (maybe even taking equation of time into account, but that I have not checked). A while back, Puybaret and I compared notes (after the blogpost about sunlight simulation) - and results seemed to be spot on. For instance, the evening sun disappears from my terrace exactly when SH3D rendering tells me it will. (Decimal grid, with standard GPS datum - wgs 84 - and true North - but in most cases this is default, and differences from earlier European Datum is marginal. The three digits in SH3D means the North/South position will be accurate to 111 metres, East/West even more accurate the further North you get. This accuracy is insufficient for navigation, but good enough for sunlight rendering). So for accurate sunlight rendering, do get the settings right: Should you be 5° off E/W, the sunset will be wrong by 20 minutes, and sun height (i.e. how much sun comes in the windows at different times of year) is significantly different in Northern Europe from the Med. If there are trees or other obstacles outside the home, location is key to finding out about sun and shade through the year.
But getting the settings right is easy if you use a gps (on a mobile phone if you like, wait for gps to get a proper fix) or are familiar with navigation/maps. Actually, it is easy even if you are not:
EASY APPROACH TO CORRECT SETTINGS:
Geographic location (position): Find your home on OpenStreetMap. Click on the location and zoom all the way in. The URL will now look something like this: www.openstreetmap.org/#map=19/51.27987/1.08279: 51.27987 is degrees North and 1.08279 is degrees East (in this case, Canterbury Cathedral). Numbers will be negative for South and West. (The location can also be read from other online maps, albeit with a slightly different procedure. If the location is given in Degrees/Minutes, like Cec' link, the position must be converted to decimal: same degrees, multiply the minutes by 1,6666667).
North direction in degrees: can be read from the map, but the easiest is probably to use a compass aligned with the wall to read the degrees. Most phones come with a compass that is pretty accurate - exactly how it works depends on your compass/gps app.
This may sound a bit geeky. But correct settings are important not only for the sunlight rendering. Getting the position and direction right will also determine how to place a dish antenna, a terrestrial antenna, solar panels of all sorts, choice of windows' light emission, need for awnings etc. For instance, our satellite dish is totally hidden far back on a side wall with a very narrow margin. Were the wall at a slightly different angle, we would have had to place it in the middle of the facade. Solar and antennae calculations will require some additional work, but usually pretty straightforward to figure out with available online calculators (or playing around with some basic astronomical navigation  ).
ok
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