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AppGameKit Studio Chat / Coordinates to km (or miles)

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jlahtinen
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Posted: 27th Jul 2021 12:03
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I tested few formulas to convert map coordinates to distance in km, but all formulas return 0 in AGK.



What I am doing wrong here?

Original:

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Conjured Entertainment
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Posted: 27th Jul 2021 12:52 Edited at: 27th Jul 2021 13:11
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where were values given to the lat's and lon's ???

If those values are zero , then the result of that formula will be zero.

Yes there are other numbers being given in the formula (6371 and the 0.174...), but those rad's are being multiplied by the lon's and lat's before they computed otherwise, so they would be zeros before the other additions, subtractions etc are being done, leaving you adding and subtracting zeros, leaving a zero to multiply by the 6371, again resulting in zero.


EDIT
I just ran a test on the first snippet, and I did get results other than zero once I gave values to the lat's and lon's

So, you should be okay if you make sure all of those <> 0 before doing the calculation.

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jlahtinen
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Posted: 27th Jul 2021 13:11
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Ofcourse the values must be given...

Whole code:



For example these values give: "-nan(ind)"
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Conjured Entertainment
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Posted: 27th Jul 2021 13:20 Edited at: 27th Jul 2021 13:49
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Of course..lol

The problem with those values is the lon2 seems to be messing it up.

If I reduce that value then it works, so it is somehow throwing it out of range?

I am not good with the cos and sin formulas..

Sorry I couldn't help.

EDIT

I used whole numbers on the lon's and lat's and reduced the length of the rad's digits and got better results

So maybe the length of those is what is throwing it our of range... not sure why if the lengths are fixed for floats, but it did not give the "-nan(ind)" result

Tried it again with the full length rad using whole numbers for long and lat and didn't get the " -nan(ind)"

I tried once again leaving the full length of all numbers, but removed the decimal thus making the longs and lats huge and it still did not give the "-nan(ind)" result

So, you may want to use whole numbers to keep this in range of the math capabilities then place those decimals yourself afterwards

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Virtual Nomad
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Posted: 27th Jul 2021 13:44 Edited at: 27th Jul 2021 14:02
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converting this:

seems to work?
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jlahtinen
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Posted: 27th Jul 2021 13:45
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Yeah, with some coordinates it gives some results (but not right).

Tried 3 different formulas and none of them work with AGK. AppGameKit precision error maybe... I have no idea.


Another:

https://www.geeksforgeeks.org/program-distance-two-points-earth/
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jlahtinen
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Posted: 27th Jul 2021 13:49
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Quote: "converting this:

+ Code Snippet
seems to work?"


This works fine!

Massive thanks, I'll bet this is useful to others too.

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Virtual Nomad
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Posted: 27th Jul 2021 13:57 Edited at: 27th Jul 2021 14:03
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double-check it where i'm still on my first cup of coffee this morning

otherwise, i've never played with this but i'm seeing lat/lon using north/south & e/w so how does this account for that?

then, with your original post, whenever i see integers mixed with floats i get nervous that something is being cast as an integer. not saying that was the issue with yours but best habit when expecting to return floats is to use all floats. (just edited my code above to use "all" floats. i'd missed a couple )
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Conjured Entertainment
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Posted: 27th Jul 2021 14:02 Edited at: 27th Jul 2021 14:08
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EDIT
Never mind...

Virtual Nomad already found a solution.


My work around would not have been any good anyway, now that I see that longitudes and latitudes are not uniform units of measure.

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jlahtinen
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Posted: 27th Jul 2021 18:47
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Quote: "longitudes and latitudes are not uniform units of measure."


Yes, it's pain.

Quote: "double-check it where i'm still on my first cup of coffee this morning

otherwise, i've never played with this but i'm seeing lat/lon using north/south & e/w so how does this account for that?

then, with your original post, whenever i see integers mixed with floats i get nervous that something is being cast as an integer. not saying that was the issue with yours but best habit when expecting to return floats is to use all floats. (just edited my code above to use "all" floats. i'd missed a couple )"


Actually this formula is off also, like 10km in 30km distance when comparing to Google maps (you can measure direct distance with right mouse click). Not your mistake ofcourse.
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Virtual Nomad
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Posted: 28th Jul 2021 03:20
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Quote: "Actually this formula is off"

after i read THIS, i claim THIS

meanwhile, the Haversine Formula above "determines the great-circle distance between two points on a sphere given their longitudes and latitudes. Important in navigation", it's seemingly obvious that it's use is "earthly" (while earth is not a perfect sphere - which i doubt google maps contemplates but it may be considering changes in elevation/undulation which would affect the "driving distance" it's generally used for).

being off "10km in 30km distance" is unacceptable but i personally don't know where to go from here...

if you find a formula (that you agree with since it appears you want it to agree with google maps), i would be happy to help convert to AppGameKit, otherwise
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blink0k
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Posted: 28th Jul 2021 04:22
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I wonder if the google maps api has a function for this?
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Virtual Nomad
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Posted: 28th Jul 2021 04:44 Edited at: 28th Jul 2021 04:53
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Quote: "I wonder if the google maps api has a function for this?"

all that i see is the distance matrix which follows routes (vs a straight line).
Quote: "If you pass latitude/longitude coordinates, they will snap to the nearest road. "


same for OSMR which i may tinker with since i dont believe it requires an API key.
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Conjured Entertainment
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Posted: 28th Jul 2021 11:56 Edited at: 28th Jul 2021 12:09
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Earlier, I had suggested just using vector distance like you would two points on a 2d representation such as our screen .

Then, I realized that the longitudes are only uniform at the equator,

So, the vector thing wouldn't work unless you plot off the four unions forming a trapezoid for that section using an array or table of the distances between each point.

Then you could do some triangulation off the corners.

Yeah the earth is not a perfect sphere, but each distance between two longitude lines (meridians) should be uniform for each latitude (generally speaking) so you wouldn't need values for every one, just one value for them all for each latitude. (vice versa)

Search "table of differences in distance for longitudes" to find more info to build your array. (or keep searching for a formula that gives accurate results)

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jlahtinen
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Posted: 31st Jul 2021 13:26
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Yeah, it's weird claiming that the formula is +-0.5% accurate if it depends being near equator (or something). It's more baffling that basically everyone on stackoverflow agrees and claims it's accurate (and I cant post there, need some "reputation" or something, dont care).

Have to keep digging into it.
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Phaelax
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Posted: 1st Aug 2021 14:49
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Have you looked at this?
http://edwilliams.org/avform147.htm

I guess that's what they used to build the calculator on this site: https://www.nhc.noaa.gov/gccalc.shtml?
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