Android Question Help with some b4A Calculations

daniedb

Active Member
Licensed User
Hi Guys

I'm busy converting one of my windows Coordinates Programs for Racing Pigeons from a Windows program to B4A
I got stuck with some calc convertions.

B4X:
sub Globals
     Dim Deg2Rad As Double  'EQUATE(.0174532925199) ! number of degrees In a radian
     Dim a As Double  '  EQUATE(6378.14) ! the earth's radius in kilometers
     Dim fl As Double  '  EQUATE(.003352813) ! the earth's flattening
     Dim lat1 As Double  '  REAL ! latitude of departure
     Dim lat2 As Double
     Dim North1  As Long  '  Short(0) ! latitude of departure Northern Hemisphere
     Dim South1  As Long  '  Short(1) ! latitude of departure Southern Hemisphere
     Dim West1  As Long  '  Short(0) ! longitude of departure Western Hemisphere
     Dim East1  As Long  '  Short(1) ! longitude of departure Eastern Hemisphere
     Dim lon1 As Double  '  REAL ! longitude ofdeparture
     Dim North2 As Long  '  Short(0) ! latitude of destination Northern Hemisphere
     Dim South2 As Long  '  Short(1) ! latitude of destination Southern Hemisphere
     Dim West2  As Long  '  Short(0) ! longitude of destination Western Hemisphere
     Dim East2  As Long  '  Short(1) ! longitude of destination Eastern Hemisphere
     Dim lon2  As Double  '  REAL ! longitude of destination

     Dim F As Double  '  REAL ! (lat1 + lat2)/2
     Dim G As Double  '  REAL ! (lat1 - lat2)/2
     Dim lambda As Double  '  REAL ! (lon1 - lon2)/2
     Dim S As Double  '  REAL
     Dim C As Double  '  REAL
     Dim tan_omega  As Double  ' REAL
     Dim omega As Double  '  REAL
     Dim R  As Double  '  REAL
     Dim D As Double  '  REAL ! approxomite Distance In kilometers
     Dim H1  As Double  '  REAL
     Dim H2  As Double  '  REAL
     Dim km  As Double  '  decimal(12,3)!REAL(0) ! the Distance In kilometers
     Dim mi  As Double  '  REAL(0) ! the Distance In miles
     Dim Meter As Double  '  Decimal(12,2)
  Dim coord As Double 

end sub

Please see the code and advice. Appreciate

'* - lines working
'X - lines with errors


B4X:
Sub Distance
  F = (lat1 + lat2)/2    '*
  G = (lat1 - lat2)/2    '*
  lambda = (lon1 - lon2)/2

  ' convert To radians
  F *= Deg2Rad   'X
  G *= Deg2Rad  'X
lambda *= Deg2Rad 'X

  S = Sin(G)^2 * Cos(lambda)^2 + Cos(F)^2 * Sin(lambda)^2   'X
  C = Cos(G)^2 * Cos(lambda)^2 + Sin(F)^2 * Sin(lambda)^2   'X

  tan_omega = Sqrt(S/C) '*

  omega = ATan(tan_omega) '! In radians '*

  D = 2*omega*a ' approximate Distance In kilometers   '*
  R= Sqrt(S*C)/omega    '*
  H1 = (3*R - 1)/(2*C)  '*
  H2 = (3*R + 1)/(2*S)   '*


km = D *(1 + fl*H1*Sin(F)^2 * Cos(G)^2 - fl*H2*Cos(F)^2 * Sin(G)^2)  'X
  mi = km/1.609344
  Meter = km * 1000
End Sub

If interested, here is my original WIndows App
www.leznadsoftware.co.za/downloads/calcdist.zip
This program is pretty accurate, for distance between 2 Coordinates


Thanks, Appreciate
Danie
 
Last edited:

derez

Expert
Licensed User
The coordinates should be of type double, not long
F *= Deg2Rad 'X -> F = F * Deg2Rad
Sin(G)^2 -> power(sin(G) , 2)

I think that type "location" with these methods will give you what you need easily :

Initialize2 (Latitude As String, Longitude As String)
Initializes the location object with the given Latitude and Longitude.
Values can be formatted in any of the three formats:
Degrees: [+-]DDD.DDDDD
Minutes: [+-]DDD:MM.MMMMM (Minute = 1 / 60 of a degree)
Seconds: [+-]DDD:MM:SS.SSSSS (Second = 1 / 3600 of a degree)
Example:
Dim L1 As Location
L1.Initialize2("45:30:30", "45:20:15")



DistanceTo (TargetLocation As android.location.Location) As Float
Returns the distance to the given location, measured in meters.
 
Last edited:
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derez

Expert
Licensed User
You can also save on translating deg to rad by using trig functions with D : SinD(deg) instead of sin(rad) etc.
 
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daniedb

Active Member
Licensed User
Derez

Had a look at location. Will defnitily use in the future
Do I understand this correctly.
Initialize2, will take the lat/lon entered
Distanceto, will give the distance from current gps location to Coordinates in Initialize2?

Correct?

I want to enter 2 different coordinates (No GPS required) and workout the distance!
Dont see any function for this in Location?

Thanks
Danie
 
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derez

Expert
Licensed User
Initialize2 tells Location "where it is". It is not connected to gps unless you put the gps coordinates there by code.
DistanceTo measures the distance from "where it is" to the target. So, each target you put in DistanceTo will measure the distance to that target, endless possible number of points...
 
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daniedb

Active Member
Licensed User
Thanks Derez.
Pitty I haven't found this earlier. Would save me hours.

Got is going, Appreciate your help

It doesn't seem that accurate, right? or my "real" GPS is not accurate?
I'm out by about 100 meters, but thats close enough for what I want


Cheers
Danie
 
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derez

Expert
Licensed User
GPS accuracy should be much better at least 10-30 m, but that is when you have good reception of sattelites.
Make sure you are not rounding the data by using int or long instead of double.
 
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