how to Convert Lat ,long to an XY coordinate system (e.g. UTM) and then map this to pixel space of my Image

Question

I have a very small area map , which I downloaded from Openstreet map(PNG) and also its OSM(.osm) file which contains its Lat ,long.

Now I want to convert Lat ,long to an XY coordinate system (e.g. UTM) and then map this to pixel space of my Image which is of size (600 x 800 ). I know its a two way process ,like to know how to do this . Thank you

Bellman

Answer 1

GPS Coordinates to Pixels

• Assuming this map does not cross prime meridian
• Assuming pixel 0,0 is upper left, and pixel 600,800 is lower right.

• Assuming map is Northern Hemisphere Only (no part of map is southern hemisphere)

  1. Determine the left-most longitude in your 800x600 image (X)
  2. Determine the east-most longitude in your 800x600 image (Y)
  3. Determine Longitude-Diff (Z = Y - X)
  4. Determine north-most latitude in your 800x600 image (A)
  5. Determine south-most latitude in your 800x600 image (B)
  6. Determine Longitude-Diff (C = A - B)

Given a Latitude and Longitude, to determine which pixel they clicked on:

1. J = Input Longitude

2. K = Input Latitude

3. Calculate X-pixel

   XPixel = CInt(((Y - J) / CDbl(Z)) * 800)

4. Calculate Y-pixel

   YPixel = CInt(((A - K) / CDbl(C)) * 600)

UTM

Here is a cartographic library that should help with GPS to UTM conversions

Cruzcruzado

thanks for answer ..Similar to what you said above I already converted my Lat ,Long to Image X and Y . But if you see my question ,first thing is how to convert the Lat,Long to real world X,Y( UTM ) and then Map that to my image X,y ... Because I do certain processing using UTM(x,y). – Bellman

See this cartographic projection library for help with the conversion to UTM. Sorry I misunderstood your question. trac.osgeo.org/proj I don't know a solution for going to UTM then to pixels – Cruzcruzado

Looks interesting, but costs $$ eye4software.com/products/gpstoolkit/source/vcnet/utm – Cruzcruzado

here what are the steps 3 and 4 . ? ie CInt,CDbl ?? – Stanch

CInt converts the inner value into an integer, CDbl converts the inner value to a double-precision floating point – Cruzcruzado