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: 1135

☇ 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

Help Keep Us Alive and Free!

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

charlie-jm commented on Thiago Paim's photo
Land Survey Media Thumbnail

Brazil Surveying in VW

"es total station by topcon "
2 hours ago
kenneth foong joined Malik Abdur Rehman's group
Land Survey Media Thumbnail

Excel Spreadsheets for Surveyors

This group is for discussions related to the use of spreadsheets and excel in land surveying.See More
9 hours ago
kenneth foong replied to Durai Kannan's discussion STAR NET PROCESSING in the group Excel Spreadsheets for Surveyors
"You can try use this FRT to covert start net format."
9 hours ago
Profile IconBrad Martin, Gerald Bernhard, Saqib Wazir and 2 more joined Land Surveyors United
11 hours ago
Mike McCulley promoted LSU Justin's group Topcon Support Group
21 hours ago
Desmond Elliott updated their profile
23 hours ago
Achilles Nizamopoulos replied to Achilles Nizamopoulos's discussion survce localization problem
"Hello Desmond, thanks for the reply. i am tryin gto follow tour steps. how do you procces the RINEX…"
Surveying Jobber's video was featured

Precision and Accuracy in Geodetic Surveying

This brief video, produced in collaboration between NOAA’s National Geodetic Survey and The COMET Program, is aimed at surveying professionals, planners, policy-makers and others who use mapping products. The video emphasizes that survey…
Gennady's 2 photos were featured
ePalmetto shared their page on Tweet This
Jacquelin RAMAROLAHY's discussion was featured


Hi all,Did you already have any experience with this device? which software is fit better to read…See More
LSU Justin shared Charles Carpenter's discussion on Tweet This
Gennady was featured
Julius's photo was featured

Camel Crew

"collecting assumed X,Y,Z on disturbed borehole (geophysical survey point) inside camel cage"
ePalmetto promoted Julius's photo
ePalmetto shared Julius's photo on Tweet This
Brian Loucks joined LSU Justin's group
Land Survey Media Thumbnail

California Land Surveyors

California Land Surveyors group is a discussion forum for land surveyors who live and survey in the…See More
Brian Loucks updated their profile photo
Profile IconBrian Loucks, kayveen murithi, Marcello Cesaratto and 5 more joined Land Surveyors United
LSU Justin shared Charles Carpenter's discussion on Tweet This

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