[TowerTalk] HFTA Disc....

Sun Jul 17 10:06:46 EDT 2016

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 at 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 at contesting.com] On Behalf Of
>StellarCAT
>Sent: 17 July 2016 12:51
>To: towertalk at 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 at 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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