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Terrain Data Fixed!

It's been a long time coming.

If you've ever looked at the Longley-Rice coverage maps in or near Des Moines, IA; Providence, RI; Florence, SC; or Gainesville, FL; you've probably noticed that they have odd diamond-shaped areas where the maps just look wrong. What's wrong is that the SRTM-3 data that is used by SPLAT to create those maps has diamond-shaped holes in it in those places. Using functions SPLAT has for handling it, I had patched in other lower-resolution data, and while it helped, it still wasn't really correct.

Yesterday I got a question from a friend about where the SRTM-3 data had moved to, since the links on the SPLAT webpage are dead now. I went looking and found it, but then I noticed a message that said the data had been updated in 2015 and now had some of the holes in the data have been patched. I grabbed the files that cover the Iowa hole, which was the worst of the four, and reran one of the maps. Sure enough, the hole there is now patched and the maps came out looking correct.

I'm in the midst of rerunning the maps that were impacted by that issue in Iowa. As of this writing, I've also grabbed the patched terrain for the South Carolina hole, and tested it on WBTW to prove that hole is also patched. Once I'm done with Iowa, I'll move on to South Carolina. I also intend to fix the maps in Florida and Rhode Island, but I'll do those after South Carolina is done. I'm going in order of how offensive I found the missing data to be; Iowa was clearly worst, but the other three are all somewhat minimal just because of how close to sea level the terrain is in those places. I personally found the South Carolina one to be most jarring, followed by Florida (pretty flat), followed by Rhode Island (decent portion of the diamond was in the ocean anyway).

It's going to take some getting used to the fact that those maps are now correct. It's been wrong for literally the last 15 years and I'm very used to it. I also want to note that there is at least one additional hole that I'm aware of in the US, in southwest Texas, but as I recall there are few or no TV stations that reach it, so I'm not sure if I'll need to do much there.

Finally, there was also a separate flaw in the terrain near the Salton Sea in California. I've tried replacing the terrain data with newer data here as well and the issue appears to be resolved per the KESQ map I ran. I'll be rerunning maps in that area as well.

UPDATE (2/16/2023 at 3:08PM ET): So the Iowa maps should be done. Let me know if you spot any I missed. I am in the midst of rerunning the Yuma stations impacted by the Salton Sea issue. I reran WBZ to test the Rhode Island fix and am happy with it. I reran WUFT and WXGA to test the Florida fix and I'm not as happy with that one. I'm going to think on that one a bit and focus on the other areas before deciding what to do there. In any event, expect to continue to see replacement maps near Florence, Providence, and Palm Springs in the coming days.


1. On Wednesday, March 15 2023, 11:08 by Douglass Allen

Thanks Trip, Great maps now even better!
Doug K4LY Inman, SC