How to set reference system for {x},{y},{z} PNG raster images

Question

I have a set of PNG images downloaded from a service like:
http://tile.openstreetmap.org/{z}/{x}/{y}.png
The images are named:
09_118_180.PNG
09_119_180.PNG
etc.

How can I combine these image in FME and project them correctly?

Answer 1 · 2019-05-31T13:54:57Z

Best Answer

Answer by jdh · May 31 at 01:54 PM

OSM uses a slippy map.

To go from tile numbers to lat long use the following equations:

n = 2 ^ zoom lon_deg = xtile / n * 360.0 - 180.0 
lat_rad = arctan(sinh(π * (1 - 2 * ytile / n))) 
lat_deg = lat_rad * 180.0 / π

This returns the NW corner of the image. You can use xtile+0.5 and ytile+0.5 to get the center of the tile

Add comment · Show 2 · Share

10 |4000 characters needed characters left characters exceeded

Attachments: Up to 10 attachments (including images) can be used with a maximum of 4.0 MB each and 4.0 MB total.

jdh · May 31 at 04:47 PM 0

Share

Personally I would calculate all four corners and use the RasterGeoreferencer and then the RasterMosaicker, then use a CoordinateSystemSetter to define the projection as EPSG 3857.

yvrig · Jun 03 at 06:53 AM 0

Share

Works like a charm, thank you!
I ended up not using the RasterMosaicker as it opened too many files which would require to use the Mosaicker in two steps. Instead I vectorized each raster individually and combined the results at the end, which probably also is faster for my scenario.

capture-fme.png (107.7 kB)

How to set reference system for {x},{y},{z} PNG raster images

1 Reply

Follow this Question

Related Questions