yes - I'm aware you can remove oversampled flat regions or shadow points as
long as they're far enough away and/or they're far enough down from the
previous high point to avoid removing defraction effects ... but where I'm
at now is - I created 10 m point plots - and I used those with HFTA... so -
actually looking at the PRO files I can see that indeed somewhere something
changed the steps to 30M! So first my apologies Shawn for saying otherwise!
I know I downloaded the 1/3arcsec file ... and thought I had used Microdem
correctly ... how then does it end up not using this data and 'crashing'?
Either Microdem didn't create 10m steps (I screwed up or it has its own
limitations that I wasn't aware of nor saw in the help file) or HFTA
massaged the data files somehow changing them to 30M by using every third
point. The latter is extremely unlikely as I'm sure it would say it was
doing this to avoid confusion.
Does Stu, TU, do this for you in his plots that his site creates?
Gary
-----Original Message-----
From: Ian White
Sent: Sunday, July 17, 2016 8:43 AM
To: 'StellarCAT' ; towertalk@contesting.com
Subject: RE: [TowerTalk] HFTA Disc....
HFTA does not require evenly spaced data points, so the 149-point limit in
the data file is not the problem it might seem. If you are prepared to
remove some redundant data from the computer-generated file, you can often
reclaim space to insert important local detail that the satellite surveys
had missed.
Redundant data includes:
* All but the first and last points from a string of data showing the same
height (so a large body of water can be represented by just two points near
the opposite shores, and HFTA will interpolate as needed).
* All intermediate data points on a uniform slope (these opportunities are
harder to notice in the file, but they may well be there)
* Excessively dense data at great distances (it makes no sense to use the
same point spacing at the far horizon that you're using close in).
* Everything beyond the horizon (it is advisable to leave a few points in
just beyond the ridge line to allow for diffraction, but distant locations
in 'deep shadow' can be safely ignored).
Always keep back-copies, of course, and always check for the effects of your
editing on the computed results.
And having done that, you can then insert some new data points close-in
where it matters, based on your own local knowledge. For example, I deleted
a 'hill' which was actually a clump of tall trees (replacing that data point
with the true ground level) and inserted new data points to represent a
sharp drop-off which the satellite data had missed.
73 from Ian GM3SEK
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
StellarCAT
Sent: 17 July 2016 12:51
To: towertalk@contesting.com
Subject: Re: [TowerTalk] HFTA Disc....
Yes but to Shawn's point there is an arbitrary limit to the number of
points
allowed. I had a friend in CO ask me to do a plot for him using MicroDEM
and the 10 meter points (1/3 arcsec) ... he had distant mountains that
didn't show in the normal 14,000' range ... but when I tried to go out
further, using this with HFTA it told me there was a limit to 149 points. I
had never seen that before in my use - using 10 meter and 5 deg
increments... but to Shawn's point in a reply today, something I hadn't
thought about with my runs, 4400M (14K' roughly) would be 440 points if it
was 10 meters and 147 if 30 meters... so it might very well be that it
truncated the data using only every third one and all this time I had been
believing I was using 10 meter points!
My plots look quite undulated and match a topo map ... but I can now
easily
see that it could very well be 30 meters since the major demarcation points
are 1000'!
This would be the first thing I'd like to see changed - take it, change it
so that it can use the 10 meter data out to the full extent.
Gary
-----Original Message-----
From: Jim Brown
Sent: Saturday, July 16, 2016 7:28 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] HFTA Disc....
Gary,
When I was running HFTA on my QTH in the Santa Cruz mountains, Dean
advised me to to out to 10-15 miles. This ignores small variations, like
the gullies being described. The radial data is a plain text file, and
it is possible to generate your own data from topo maps. When I started
using HFTA, I did a few radials this way as an exercise.
73, Jim K9YC
On Sat,7/16/2016 3:03 PM, StellarCAT wrote:
I use the 10M range data with HFTA exclusively! The 30 is far too long of
a sample point. I'd prefer even smaller if available. I set up microdem
at
5° increments and never have a problem getting the full data set. Works
great.
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