Anyone know how to do a Find My Car type of app?

Getting Started Newbie Questions
#1

Hello,

I need to use the gps on my phone to have an arrow point the direction do a set of gps coordinates I have just like they do for a Find My Car type of app. I am not doing that app but using the same methods for another app.

I need to point an arrow in the direction and also calculate the distance in feet or yards to that destination.

Does anyone know where I can find some code example for this? I know there is a compass example with Corona. But I want to point to a set of coordinates, not the degrees.

Thanks,

Warren

#2

I found this website that gives the bearing which is what I need. Now I just need to figure out how to do this in Corona with lua. Has anyone else done this?

http://www.movable-type.co.uk/scripts/latlong.html

#3

Try these two functions:

local function angleBetween( srcX, srcY, dstX, dstY )
    local angle = ( math_deg( math_atan2( dstY-srcY, dstX-srcX ) )+90 )
    return angle%360
end

local function distBetween( point1, point2 )
    local xFactor = point2.x-point1.x ; local yFactor = point2.y-point1.y
    local dist = math_sqrt((xFactor*xFactor) + (yFactor*yFactor))
    return dist
end
 

#4

Its really all about right angle math.  This is a great site:  http://www.mathwarehouse.com/geometry/triangles/right-triangle.php

While on a planetary scale, you have to factor some curve into the distance, in most uses (within a few miles of two points), the world is flat enough that right angle math is accurate enough.

Rob

#5

Thanks! I am calculating the distance and bearing only within 3 miles at the most. And as I move closer to the destination it is updating the bearing so any errors will be narrowed down as I get closer. I am trying this now and will let you know as well as anyone else how it works.

Warren

#6

Given that GPS coordinates are inherently inaccurate anyway (for security purposes), Any curvature errors are going to be insignificant.

Rob

#7

The bearing part works great. How do I use the distance with lat/lon for each point?

#8

In the distance function it takes two x, y points.  You have two x, y points, with latitude being the .y and longitude being the .x.

Rob

#9

You can also use the Haversine Formula to get the approximate distance between two GPS points.

I provided the code in this forum post: http://forums.coronalabs.com/topic/53446-distance-find-in-location/?hl=haversine#entry277901

#10

I have some bearing code that works with long/lat here http://simon.fearby.com/blog/?p=2117

#11

Nice post!

Rob

#12

I found this website that gives the bearing which is what I need. Now I just need to figure out how to do this in Corona with lua. Has anyone else done this?

http://www.movable-type.co.uk/scripts/latlong.html

#13

Try these two functions:

local function angleBetween( srcX, srcY, dstX, dstY )
    local angle = ( math_deg( math_atan2( dstY-srcY, dstX-srcX ) )+90 )
    return angle%360
end

local function distBetween( point1, point2 )
    local xFactor = point2.x-point1.x ; local yFactor = point2.y-point1.y
    local dist = math_sqrt((xFactor*xFactor) + (yFactor*yFactor))
    return dist
end
 

#14

Its really all about right angle math.  This is a great site:  http://www.mathwarehouse.com/geometry/triangles/right-triangle.php

While on a planetary scale, you have to factor some curve into the distance, in most uses (within a few miles of two points), the world is flat enough that right angle math is accurate enough.

Rob

#15

Thanks! I am calculating the distance and bearing only within 3 miles at the most. And as I move closer to the destination it is updating the bearing so any errors will be narrowed down as I get closer. I am trying this now and will let you know as well as anyone else how it works.

Warren

#16

Given that GPS coordinates are inherently inaccurate anyway (for security purposes), Any curvature errors are going to be insignificant.

Rob

#17

The bearing part works great. How do I use the distance with lat/lon for each point?

#18

In the distance function it takes two x, y points.  You have two x, y points, with latitude being the .y and longitude being the .x.

Rob

#19

You can also use the Haversine Formula to get the approximate distance between two GPS points.

I provided the code in this forum post: http://forums.coronalabs.com/topic/53446-distance-find-in-location/?hl=haversine#entry277901

#20

I have some bearing code that works with long/lat here http://simon.fearby.com/blog/?p=2117