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Background: I have generated a static map (map.png) of a particular city using mapnik and osm data of the highest zoom level. I am able to zoom in and zoom out successfully using my Java program. It is an offline desktop application.

Question: I want to represent a point at a particular latitude and longitude on this map. How do I do it?

I went through the following references: http://wiki.openstreetmap.org/wiki/Zoom_levels http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#Resolution_and_Scale How to plot a point on a static Google map [png]?

I'm still not able to understand how to plot it on a static map by calculating a specific latitude and longitude at a particular zoom level with the image having a specific pixel width and height.

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from what I understand, you have a single ungeoreferenced image, and you want to find the extent.

This can be done in QGIS

QGIS - Using Capture Coordinate

If this is an urban map with details in the corners, you can manually match up the corners using the Capture coordinate plugin.

  • start with an empty project

  • Install the OpenLayers plugin (this goes in the Web menu), and use this to show OSM for the region around your city

  • Install the "Capture coordinate" capture plugin, and bring up the Capture coordinate panel using the Vector > Coordinate Capture. You might want to set the sampling to EPSG:4326 to get traditional latitude, longitude coordinates

  • For two corner points on your png (diagonally opposite), look at the corner of your png and find its position in OSM, panning and zooming as required.

  • click on 'start capture', then click on the point corresponding to the corner of your image

  • once you have two diagonally opposite corners' coordinates, it's now simple maths to interpolate a pixel position to/from lat, lon

QGIS - Using georeferencing

This is a little more advanced, but will give you results if it's not possible to exactly pick out where the corners are (for example, if it's empty ground or in the sea)

  • start with empty project
  • use OpenLayers plugin to display OSM as before
  • install the Georeferencer plugin
  • start it up with Raster > Georeferencer
  • load in your png raster (first icon)
  • find some landmark on your png as close as possible to one corner- a building, for example, or a road junction
  • click on add point, and in the dialog check 'from map canvas'. If you have a mouse wheel you can pan with that. Click on the corresponding place in the OSM map.
  • repeat for the other 3 corners
  • see the GCP table? Those are your coordinates ('ground control points')
  • click on Transformation settings, and set up where you want to save the raster. You might want to change the crs to EPSG:4326 if you want lat,lon.
  • click on the Run icon (green arrow)
  • you'll now have a georeferenced tiff.

There's quite a good step-by-step guide here, although it's a bit out of date.

Now if you open this geotiff (add as a raster layer) you go into properties and you'll see your extent.

  • I appreciate your response. But suppose I need to find out lat/long at a zoom level without using an external application, how do I do it? I have with me : static image.png, known zoom level, bounding box, image width and height at the highest zoom level. – suhas bhairav Aug 4 '15 at 7:37

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