Hi fellows,

We have some queries to answer some technical issues regarding solar observation to compute/obtain azimuth of an observed station and how convergence angle applied to the computation of grid azimuth.

1. What is the azimuth reference computed from a solar observation?

2. How to apply convergence angle when the observed stations is in the left or right in the central meridian and how it differ from each other? 

3. What is the difference between true north, grid north and magnetic north?

4. What is the  azimuth reference used in executing a traverse for a meridional block survey?( Meridional blocks are defined by each geographic coordinates and later converted to grid coordinate.)

Thank you fellows.

Find Similar Content by Clicking These Tags ☟
Subject Tags: azimuth, observation, solar, surveying

This Content Originally Published to Land Surveyors United Network

Views: 1237

☇ Reply to this

Replies to This Discussion

Are you familiar with a  document titled " Astronomical Observation Handbook" by Charles Ghiliani? It describes the techniques a surveyor needs to know for determining azimuths, north, etc using astronomic observations. If you send me your email address I can send you the pdf. It's only about 17 pages long.

Please send me the PDF . Much obliged Arthur Will

Here's the document.

Download Survey Documents-Members Only


Here's the document.

Download Survey Documents-Members Only

Hi Carlos, i saw your mail regarding the document, and it is an important helpful document. I kindly ask if it is possible to email the document to me as well. my email _ [email protected]


Thank you

Here are the two relevant documents.

Download Survey Documents-Members Only

Here are the two documents discussed.

Download Survey Documents-Members Only

Hi Carlos, maybe that would be helpful document. Please send at [email protected] Thank you bro.

Separately, I sent you the document I originally noted. I just located another paper in my files on Astronomic Geodesy, which I am attaching here, and maybe provides more help.

Download Survey Documents-Members Only

It's been 30+ years since I last did one, so I will defer to the instructions provided by others.  I will however tell you that the results we got were very impressive. 

We had a 25 mile Geodetic control Survey in Upstate NY in early 80's.  One of our party members was from Ghiana, (British Scholl of Survey), so if I remember correctly they could not observe Polaris or Southern Cross as they were so close to the Equator.

In any case he had a program in his TI 59 that we used.  We scaled a lat/long from a quad and used a Radio Shack time cube (remember them?) and used a T2 and Rolffs solar prism.  We observed azimuths on 4-5 of our legs that were adjusted from the 25 mile Geodetic traverse.

The results on the Solar vs. conventional were all with less than 10 seconds of the adjusted conventional control.

Pretty neat stuff.

Let us know how you make out. 


In brief terms Astronomic azimuth is true north; your meridional circuit is grid north, and magnetic north is the local magnetic north at any point on the earth's surface (not very useful in surveying terms but alas it is used as a reference in Australia for their cadastral surveys>>baffling!!)

True North and Grid North are related by convergence..Be very careful applying the correction you will need to draw a diagram..

At the central meridian of your grid system (meridional circuit) by definition grid bearings = astro bearings; and as we move east or west of this CM the convergence increases + or - depending on whether we go west or east.

You are in the Northern Hemisphere I take it so the convention is:

West of CM: Grid > True

East of CM: Grid < True

Southern Hemisphere:

West of CM: Grid < True

East of CM: Grid > True

To see this you will need to draw a diagram with pole (North or South depending on hemisphere), and draw location of observer P and a direction to a point say 'A'. Grid North or South is a line parallel to CM line (a meridian by definition), and True North or South the direction to the pole for the observer.

Remember that depending on the map projection you are using a different calculation of convergence may be needed but for a TM the general approx formula is:

Conv = dLong * SIN (Obs Latitude)

A scaled position of observer's LAT / LONG will be necessary to get a good approximation of the convergence at any point.

Hope this helps a bit



Land Surveyors Celebrate the Past Present and Future of Professional Land Surveying in this Geosocial Network. Frictionless GeoCollaboration

Surveyor Hubs and Tags

Surveyor Community Hubs For World Regions

Surveying Hubs For US States

Social Support For Equipment

Surveying Photos by Tag

Surveying Videos by Tag

What You Missed

Lalith Senanayake posted a photo

Survey through rubber estate

Topcon does what I need for the moment
3 hours ago
RAJA M.HALEEM MINHAS replied to Malik Abdur Rehman's discussion Radial Easting Northing in the group Excel Spreadsheets for Surveyors
"i can not fine the attached file.kindly attach it again. "
10 hours ago
Profile IconJJ Nell, Danie Du Plooy, andres carpio and 1 more joined Land Surveyors United
20 hours ago
talat promoted zainul ulum's discussion cut and fill calculation on cross section chart with vba excel
Deward Karl Bowles replied to David Chandler's discussion GPS rover in doorway problems.....
"Sounds like multi path issues and a weak solution as a result of the "masking" of your…"
Lalith Senanayake's photo was featured

Sokkia,theodolite still in operation for settigout

During a setting out,for partition case,This is handy for setting out!
Profile IconChad Erickson, Wi Pattison, David Chandler and 2 more joined Land Surveyors United
Scott D. Warner, PLS shared Deward Karl Bowles's blog post on Google +1
Jansen Loi replied to David Chandler's discussion GPS rover in doorway problems.....
"I assume you are using RTK mode in for your survey. Are you able to achieve lock or did you lose…"
ePalmetto promoted Deward Karl Bowles's blog post CHAIN! The weakest link (in the chain)
Scott D. Warner, PLS promoted Deward Karl Bowles's blog post CHAIN! The weakest link (in the chain)
Scott D. Warner, PLS commented on Deward Karl Bowles's blog post CHAIN! The weakest link (in the chain)
"Karl, Thank you for sharing your thoughts. I read your post twice and visited all the articles you…"
ePalmetto promoted LSU Justin's blog post Surveying Will NEVER Die and YOU are the Proof!
ePalmetto promoted mohammed shakeel's photo
mohammed shakeel's photo was featured

this our senior ibrahim daher

this project name is w t c qatar
Profile IconSURVEYORS "OLD"TAC BALL 1989 is the most popular photo to date


Surveyors Tac Ball, vintage "1989"
David Chandler posted a discussion

GPS rover in doorway problems.....

Our company just recently within the last year got a GPS unit for surveying....So far we have not…See More
Wi Pattison promoted Deward Karl Bowles's blog post CHAIN! The weakest link (in the chain)
ePalmetto shared their video on Tweet This
LSU Justin's 3 groups were featured

Take This Page With You

follow us in feedly

Take this Page With You

QR Code for This Page: What is this?

Surveyor Goodies

© 2014   © Created by Land Surveyors United

Badges  |  Contact LSU  |  Privacy Policy  |  Terms of Service

Related Posts for Land Surveyors UnitedRelated Posts Plugin for Land Surveyors United Network ForumRelated Surveying Photos Land Surveyors United Live Support