From: Julian Todd (julian_at_goatchurch.org.uk)
Date: Wed Jan 17 2001 - 12:33:48 CET
Received: (from mdom_at_localhost) by karto.ethz.ch (8.9.3/8.9.3/SuSE Linux 8.9.3-0.1) id NAA02512 for cavexml-outgoing; Wed, 17 Jan 2001 13:30:33 +0100 Received: from carbon.btinternet.com (carbon.btinternet.com [194.73.73.92]) by karto.ethz.ch (8.9.3/8.9.3/SuSE Linux 8.9.3-0.1) with ESMTP id NAA02508 for <cavexml_at_cartography.ch>; Wed, 17 Jan 2001 13:30:32 +0100 Received: from [62.7.115.151] (helo=gordon) by carbon.btinternet.com with smtp (Exim 3.03 #83) id 14IrjV-0004vg-00 for cavexml_at_cartography.ch; Wed, 17 Jan 2001 12:30:34 +0000 Message-ID: <00d401c08080$f7fa7750$0a3c10ac@gordon> Reply-To: "Julian Todd" <julian_at_goatchurch.org.uk> From: "Julian Todd" <julian_at_goatchurch.org.uk> To: <cavexml_at_cartography.ch> References: <3.0.1.32.20010116181528.00693dac_at_mail01.hml.aone.net.au> Subject: Re: LRUD: 'From' or 'To' ? Date: Wed, 17 Jan 2001 11:33:48 -0000 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2314.1300 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2314.1300 Sender: owner-cavexml_at_karto.baug.ethz.ch Precedence: bulk
I've done quite a bit of development on this topic.
Absolutely should not have either convention proposed.
A convention is not necessary because an example of a
form definition of cross-section location and orientation
which generalizes all conventions I presently know can be
read in http://www.goatchurch.org.uk/Tunnel/xsecto.html
This page contains diagrams.
It basically gives it in 7 parameters:
Location: station0_location + lambda * (station1_location -
station0_location)
Orientation: angle = (angle(station_fore_location - location) +
angle(location - station_back_location - location)) / 2 + adisp, tilt_angle.
Obvious adjustments made to account for one or other or both of
station_fore_location and station_back_location
being null.
Cross sections centring on a particular station set lambda = 0.
Orientations that are halfway between previous and next leg set adisp = 0,
tilt_angle = 0.
Cross sections that are horizontal, defining pitch dimensions will want
tilt_angle = 90.
The calculations for these values are reasonably trivial for a viewer
program to
follow, whereas many of the conventions require specific knowledge of
which legs connected to which station and in what order they were measured
in
order to work out which two legs it should be creating its section
halfway between.
Furthermore, LRUD defines a rectanglular cross section.
Why not have a cross section that is a loop made from
a series of points (like the kind you draw on your survey)?
Surveys that start as LRUD can write this into XML as a
rectangle or diamond: { (R, 0), (0, -D), (-L, 0), (U, 0).}
This will not preclude people recording proper
cross sections instead.
The problem with the standard conventions is that they are
unbelievably restrictive and force surveyors to
record what is clearly nonsense a lot of the time
(eg LRUD in a tall hading rift).
Sensible cross sections need not be in the vertical plane,
or centred on a station. They can be halfway along a leg,
and be tilted with the general dip of the passage.
Julian Todd.
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