Convert long/lat to pixel x/y on a given picture

Question

I have a city map of Moscow. We modified a Google Maps image with some artistic elements, but the relation between GPS coordinates and pixels remains the same.

Answer 1

The translation you are addressing has to do with Map Projection, which is how the spherical surface of our world is translated into a 2 dimensional rendering. There are multiple ways (projections) to render the world on a 2-D surface.

If your maps are using just a specific projection (Mercator being popular), you should be able to find the equations, some sample code, and/or some library (e.g. one Mercator solution - Convert Lat/Longs to X/Y Co-ordinates. If that doesn't do it, I'm sure you can find other samples - https://stackoverflow.com/search?q=mercator. If your images aren't map(s) using a Mercator projection, you'll need to determine what projection it does use to find the right translation equations.

If you are trying to support multiple map projections (you want to support many different maps that use different projections), then you definitely want to use a library like PROJ.4, but again I'm not sure what you'll find for Javascript or PHP.