as a surveyor, we maintain a "face" tag on each horizontal angular observation reading from the theodolite. The FACE attribute MUST be carried thru the data reduction of multiple horizontal angle pointings. The vertical angle (Zenith Angle) is easier to follow: 1 thru 180 implies "direct scope" and 180 thru 360 is "inverted scope". =20 I have never seen Modern electronic survey equipment output a negative Zenith Angle. A survey "Total Station" instrument is oriented either in "direct" or "inverted" FACE for any of the three types of measurements it makes: HzAngle, Zangle, SlopeDistance. By the way, 270 degees Zenith is also at station-level (horizon) We are currently attempting to create a XML that supports raw-survey-readings for our survey notes... from this rawsurveyXML we can output LandXML without having to change the LandXML spec. below is a snippet of the Zenith portion of our observation record: please note that we glom all the zeniths together, regardless of the "face"... then reduce the average to the direct face reading mode: <vert-angle zenith=3D"86.635625"> <zenith-average zenith=3D"86.635625" stddev=3D"0.00261"> <zenith-sample zenith=3D"86.637778"/> <zenith-sample zenith=3D"273.365556"/> <zenith-sample zenith=3D"86.637778"/> <zenith-sample zenith=3D"273.3675"/> </zenith-average> </vert-angle> -----Original Message----- From: John Halleck [mailto:John.Halleck@xxxxxxxx]=20 Sent: Thursday, July 17, 2003 2:06 PM To: Kevin Murphy Cc: landxml@xxxxxxxxxxxxx; john.halleck@xxxxxxxx; nathan.crews@xxxxxxxxxxxx Subject: [LandXML] Re: LandXML vertical angle clarification On Thu, 17 Jul 2003, Kevin Murphy wrote: > Date: Thu, 17 Jul 2003 13:49:57 -0400 > From: Kevin Murphy <KMURPHY@xxxxxxxxxxxxxx> > To: landxml@xxxxxxxxxxxxx, john.halleck@xxxxxxxx > Cc: nathan.crews@xxxxxxxxxxxx > Subject: [LandXML] Re: LandXML vertical angle clarification >=20 > John, > With zero directly overhead and 90 degrees on the horizon, it should > not matter > what side of the instrument you stand on. The horizon is always at 90 > degrees. I realise this...=20 But that is not what the description says. The description that Mr. Crews offers is in terms of "clockwise". Which means, as a software developer, I'm free to have the horizon -90 degrees. Rewording it to say that it=20 "Represents zenith angles with the 0 origin as straight up and measured such that the horizon is positive in the specified Angular Units" Would be closer to what I would expect in the official definition. > If you are referring to the angle if the scope of the instrument is > inverted ( reversed), > then the Zenith angle would be 360 - Z. >=20 > hope this helped... > -Kevin >=20 >=20 > >>> John Halleck <John.Halleck@xxxxxxxx> 07/17/03 01:19PM >>> > Nathan Crews says: > "Represents zenith angles with the 0 origin as straight=20 > up and measured in a clockwise direction in the specified Angular=20 > units." >=20 >=20 > If I change which side of the instrument I'm standing at, > which way is clockwise for a vertical angle changes. >=20 > I therefore find this confusing. >=20 >=20 >=20