Lighthouse

Sun Angle Issue

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I have followed instructions for plotting the sun angle but getting strange results.  I set my north arrow correctly relative to the house and lot.  I put in the latitude and longitude for west of Boston MA.  I chose Dec 20 2015 at various times of day and it seemed a bit off.   To test, I chose 7pm.   When I hit "make shadow" it shows a shadow at 7pm (screen shot attached) even though the sun sets at about 4:15pm.  How can there be a shadow?

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It looks like your Lat/Long might be off for Boston.  I used these numbers in the Sun Angle line (in addition to the north pointer) @ 7pm and did not generate a shadow.

 

Boston: 42º 35' N, 71º 05' W

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For those that may not already know this......

 

LAT and LON for any spot on the planet could not be easier. Use Google Earth. If an address is known, type it in and fly right there, otherwise navigate to location. Once location is found, center cursor over spot (house, field, wherever) and look at bottom of page where LAT LON is very accurately given.

 

LAT and LON are bottom of page. Now, in CA, "Sun Angle Specification" simply use this information and your house is now geo specifically placed on planet.

 

See example photos attached. 

 

This post was edited to correct an error I had in my explanation. If anyone read it previously, I apologize otherwise, what is written above is correct, as well as what Glenn says one post below.

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42º 23'44.56" N is just as accurately written 42.234456º N

 

71º 05'11.66" W is equal to 71.051166º W

 

 

 

 

Keith,

 

This is not correct.

The conversion between degrees, minutes and seconds and decimal degrees is a bit more complicated.

 

The conversion is D(dec) = D+M/60+S/3600

 

You can't just use the same digits and ignore the formatting..

 

Chief can handle the conversion easily by using Number Style in a dbx. 

 

eg,  42° 23' 44" converts to  42.395556° using this feature (not 42.2344º). 

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thanks, I copied the lat/long from some website, but I guess they had it wrong.  That fixed it (although, strangely, even with the correct coordinates it cast shadows at 5 pm when the sun has already set)

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I stand corrected Glenn, you as usual are correct, I will delete my post so as to not confuse anyone, but will leave this. Thanks.

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Looking at this further, you'll note that Chief drops everything to the right of seconds decimal place. If entered CA does not round this number, it simply drops the numbers to right of decimal. Example is 37.96" will get entered by Chief as 37" This can potentially be an error of 100' give or take. Not a big issue as far as sun angle goes, but if a specific location is desired, say a townhouse, you would not want to be pointing at a neighbor 3 - 4 houses over.  

 

If more accuracy is desired, and again for sun angle this really does not matter, entering degrees as a decimal will be spot on. You can use Glenn's formula above, but I found this online converter that will also do this here >> http://longitudestore.com/coordinates-converter.html

 

Within CA "Sun Angle Specification", change "Number Style" to "Degrees" 

 

CA will trim this to 6 places to right of the decimal, but will be right on for your target.

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