What's the most accurate elevation tool on the net (freebie)

alpha male · 2012-03-03T04:02:49+00:00

What elevation tool do you use and how does it compare in accuracy?I'm trying to do some antenna siting calculations ... and ... for that ... I need elevation information.However ... given any set of coordinates ... e.g., Mt Hamilton, California at coordinates 37.337408,-121.644073 ... I find the following elevation tools all give DIFFERENT elevations (some are off by more than a hundred feet!)1. Google Map API yields 1217.061889648438 meters (3992.985 feet) Geoplaner yields 1217.1 meters (3993 feet) 2. Daftlogic yields 1230.988 meters (4038.676 feet) Earthtools yields 1210 meters (3969.8 feet) 5. Heywhatsthat (SRTM db) yields 1213 meters (3980 feet) Which elevation tool do you use ... & what's the accuracy?

Mar 03, 2012 24 Replies

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Jeff Liebermann 14 years ago

True. 1 degree resolution at perhaps 20km is: tan(1deg) * 20km = 350 meters resolution. Not great resolution, but good enough for wide area coverage. For wi-fi, the range is much less, so the "squares" shown on the map will be correspondingly smaller.

Samples of wide coverage area RM calcs.

We recently moved our tower and antenna, when the building that previously supported them was demolished. So, I recalculated the coverage. I believe I used 1 degree resolution.

I'm too lazy to check the numbers right now. Maybe tomorrow. Meanwhile, this article claims that Splat is limited to 3600x3600 while Radio-Mobile is limited to 2000x2000. No clue at this time who's correct.

A 90 mile PATH (line) is quite different from a 90 mile radius coverage (area) radius.

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Jeff Liebermann 14 years ago

Looks like the balloon trackers have the same problem with Radio Mobile Deluxe.

"The 2000x2000 software elevation matrix limits paths to 2000km for 1000m data (30-arc second), 200km for 100m data (3-arc second) and 130km for 30m data (1-arc second)."

Now, go away so I can get some work done...

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Jeff 14 years ago

It is a simple click to change the step size even down to 0.01 of a degree in the polar plot, or just run a Cartesian plot where you can specify down to one pixel resolution.

Jeff

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miso 14 years ago

Yes. I'm just mentioning cranking down the angle to save someone a few meaningless runs. It didn't occur to me to do the math as you suggested, but it makes perfect sense.

I was running the beta version of splat-hd. I could do 6 degree x 6 degrees at 1/3 arc second. Each degree is 3600x3600, so I could do

21600x21600. If you want to do "mountain-topping", you need that kind of span.

Looking at the overlays I generated, I had to hack the output into 12 to

20 blocks, 3600x3600 at a time, to make it google earth compatible. Hopefully the new version does this automatically.

I believe this was the program I was trying to get to work to do the cookie cutting. Looking at the bug report, it still looks like it has issues.

I got really good with GIMP to do the cookie cutting. Still a PITA.

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