search

jmcmellen / splat

SPLAT! is an RF Signal Propagation, Loss, And Terrain analysis tool for the spectrum between 20 MHz and 20 GHz. This is a copy of the code written by John Magliacane
http://www.qsl.net/kd2bd/splat.html
GNU General Public License v2.0
74 stars 39 forks source link

srtm2sdf creates wrong filenames for files in Australia #6

Open nebukadnezar opened 6 years ago

nebukadnezar commented 6 years ago

running the SDF converter for files in Australia: srtm2sdf S31E113.hgt

creates this output file:

-31:-30:246:247.sdf

The correct filename would be: -31:-30:113:114.sdf

This behaviour occurs both on OS X and Ubuntu 16.04. I've built from the git source on both platforms, and I've also tried the pre-compiled OS X binary. They all behave the same.

Cloud-RF commented 6 years ago

It's correct as SDF longitudes are positive westings. https://github.com/jmcmellen/splat/blob/master/utils/srtm2sdf.c#L550

nebukadnezar commented 6 years ago

That is a surprising explanation. And I'm not being cynical, I'm genuinely surprised by this, and here's why: Considering plotting a topo map with the filenames changed to the actual longitudes as I suggested above in fact does create the topo map, with the correct orientation. When I leave the filenames the way they were generated, no tiles are found, and, consequently, no topo map is created. However, that, along with the absence of any mention that longitudes are in fact NOT longitudes but eastings, led me down the wrong path.

And it's snake potion units again that are causing grief - and this time in a particularly mischievous way: latitude and longitude are well established terms with globally accepted meaning. If one substitutes one of the coordinates with a different unit, a different name should be used. Call it an easting, not a longitude. If only the world could agree one day on using the same units for the same things all over the place...