Calculating distance

[abastien]

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

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?

 

[Erel]

Generally speaking, libraries should only include functions that it isn't possible to implement from code.

 

[abastien]

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.

 

[Erel]

Calculations will run faster in a library but the difference should not be too significant.

 

[Bruno]

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]

Am I right assuming that a decimal lat/lon input is required?
I think the other (dddmm.mm) format is giving me false distances...

 

[klaus]

Yes, the lat and long values must be in decimal format.

You can have a look here for other formulas.
Great-circle distance - Wikipedia, the free encyclopedia

Best regards.

 

[MM2forever]

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?

 

[Erel]

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.