Search code examples
javaandroidandroid-maps

Find out precentage of point x and y between two other points

In my android app I have simple "map", which is satellite map based image. I have exact LatLngpositions on two corners of this map: Left-Top and Right-Bottom to be precise. Now, by given LatLng point I want to create a small view add place it on the map (a marker). In order to this I have to calculate percentage x and y in pixels on my "map".

So to sum up here's my data:

LatLng MAP_LEFT_TOP; //constant point
LatLng MAP_RIGHT_BOTTOM; //constant point
LatLng location; //point, which should be inside map rectangle

What I have to calculate:

float percentageX; //percentage x position of "location" on the map
float percentageY; //percentage y position of "location" on the map

Here I found function:

LatLng interpolate(LatLng from, LatLng to, double fraction)

https://github.com/googlemaps/android-maps-utils/blob/master/library/src/com/google/maps/android/SphericalUtil.java

and I need something, which works in the opposite way. Here's my implementation, but it doesn't give me correct result (the same for y/longitude):

double findFractionX(double latitudeLeftTop, double latitudeRightBottom, double latitude){
    return (latitude - latitudeLeftTop) / (latitudeRightBottom - latitudeLeftTop);
}

Then I can get final position of the marker like this:

float imageViewWidth; //width of the imageView holding map
float imageViewHeight; //height of the imageView holding map
float x = percentageX * imageViewWidth;
float y = percentageY * imageViewHeight;

Edit: my mistake was using latitude to get x and longitude to get y while it's just the opposite.

Still something's wrong, here's how it looks in the app:

enter image description here

Here's where it should have been (I used scribble to make this example):

enter image description here

Just to make it clear I'm talking about point named "1.1", don't pay your attention for the others, they're hardcoded in the image itself.

Solution

  • Since I got another idea to write up, I'll just put both in a full answer to have more space.

    First, check if you don't accidentally switched long/lat or x/y:

    Long = x and lat = y.

    Then, how does you view look that you add? While you get the exact position of the map marker, simply adding a view to that location may look off.

    The view itself probably has a width and height itself and you may want it placed on top of the marker like when clicking on a store on Google maps? If you just put it at the calculated position, it will put its top-left corner at that position.