Calculating distance

abastien

Member
Licensed User
Here is some sample code to calculate distance between two points:

B4X:
Sub getDistanceKM(lat1, long1, lat2, long2)

   DEGREES_TO_RADIANS = (cPI / 180.0)
   EARTH_RADIUS = 6371.0
   
   rlat1 = DEGREES_TO_RADIANS * lat1
   rlong1 = DEGREES_TO_RADIANS * long1
   rlat2 = DEGREES_TO_RADIANS * lat2
   rlong2 = DEGREES_TO_RADIANS * long2
   
   '   There is no real reason To break this lot into 
   '   4 statements but I just feel it's a little more 
   '   readable.
   p1 = Cos(rlat1) * Cos(rlong1) * Cos(rlat2) * Cos(rlong2)
   p2 = Cos(rlat1) * Sin(rlong1) * Cos(rlat2) * Sin(rlong2)
   p3 = Sin(rlat1) * Sin(rlat2)

   ret = p1 + p2 + p3
   If ret = 1 Then Return 0
   
   ret = ACos(ret)
   ret = ret * EARTH_RADIUS
   
   Return ret
   
End Sub
Can we add this to the gps.dll?
 

abastien

Member
Licensed User
Generally speaking, libraries should only include functions that it isn't possible to implement from code.
I was thinking of the processing power. Would complex calculations not run faster in a library?

Just a thought - not based on fact.
 

Bruno

Member
Licensed User
Hi there,

Just a little correction for your code

" If ret >1 Then Return 0 "

My tests give me sometime 1.0000000002 :)

Bye,

Bruno.
 

MM2forever

Active Member
Licensed User
Thanks for the info klaus,
I was already searching for the mathematical/physical/geographical basis of this routine, since for me, using existing routines is great, but i like to understand what im using :)

edit://
Generally speaking, libraries should only include functions that it isn't possible to implement from code.
arent all functions of the gps lib (at least in the version i have which i guess is the latest/only one) replaceable by string operations that can be done with the b4p standart string functions set?
 
Last edited:

Erel

Administrator
Staff member
Licensed User
arent all functions of the gps lib (at least in the version i have which i guess is the latest/only one) replaceable by string operations that can be done with the b4p standart string functions set?
Yes.
Every statement has one or two exceptions ;)

If I were to write the GPS library today I would have written it as a module instead of a library. That would have made it easier to enhance it and parse other NMEA sentences.
The GPS library was written before Basic4ppc V6.50 and therefore modules weren't available at that time.
 
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