[TowerTalk] Site Elevation and TOA

[Ian White]

>On 6/18/2014 12:07 AM, David Gilbert wrote:
>> The HFTA terrain file is a very simple text file containing two
>> columns of paired numbers (one for distance and one for elevation)
and
>> is trivial to edit.
>
>Yes. When I was first learning HFTA, I generated a couple of radials by
>tracing a line, picking elevations off of a terrain map.
>
>73, Jim K9YC
>

All users should try creating a .PRO file from scratch at least once,
because creating your own file gives far more insight into how HFTA
actually uses its radial data. If you use only the SRTM data, your
understanding will remain stuck at "consumer level".

A couple of points that are in the manual somewhere, but might be
missed:

1. HFTA doesn't require terrain heights at uniform distance intervals.
It builds up the terrain profile by connecting whatever data points you
have provided, using straight lines. For intermediate distances, HFTA
will interpolate as required. 

This means a "flat terrain" profile can be created in just three lines:
(measurement units), (height at zero range) and (height at maximum
range) - for example,

meters
0 87.1
4000 87.1

Any height would produce the same results, so long as it's the same in
both lines.

2. SRTM data often requires some editing to supply local detail that the
radar didn't see - but YOU know exists, and so too did the old-time
surveyors on horseback. So once again, you need to know how to edit a
STRM-generated .PRO file to insert an extra line or two.  You can add an
extra data point at any distance (provided that the distance is greater
than the line before, and less than the line following). If the file
already contains the maximum allowable number of lines, see 1 above to
help you decide which of the other lines can be safely removed.


Try it - you'll learn something. 


73 from Ian GM3SEK