## Land Surveyor Community Forum

### Elements of projection questions

Hi all

Just lookimg for some help on a couple of questions in the elements of a projection

1. what is scale coefficient

2. what is scale error

3. what is grid scale constant

any help would be great

Cheers

Mat

You need to be a member of Land Surveyors United - Surveying Community & Forums to add thoughts!

#### Replies

• Interesting, I have a friend that retired from BLM in Alaska. He likes old vintage shotguns & rifles & wrote a number of articles in "THE DOUBLE GUN JOURNAL". I hunted pheasant,ducks & geese with him in N.Dakota. He went to Australia on a combination waterfowl & buffalo hunt which was quite successful. They made their own bismuth shot.
Modern geodetic science is the same in New Zealand as it is here or anywhere else in the world. The meanings of words & therefore the definitions seem to vary somewhat with the locality. I am still a student of the subject myself but as I understand it, a rectilinear survey such as done with a transit & tape (or theodolite & edm), does not consider curvature of the earth or the mapping angle. Geodetic surveys are based on the geoid. Latitude & longitude are the same at any elevation but coordinates based on a grid change with elevation. A grid projection is an approximation. Inverse between any two grid coordinates & the distance will usually be different than the distance between the same two points on the surface of the earth. Applying the grid factor & the elevation factor to a point will convert grid coordinates to ground coordinates or vice versa. There are various methods of reconciling the two types of surveys that have various degrees of success. As far as I can tell, the results always have some error which increases with distance.
• Hello Charlie

I think you are right what you say meanings of words & therefore the definitions seem to vary somewhat with the locality. A lot of definitions of projection elements or surveying practices i have researched for my studies definately have more than one definition, and some even contradict each other.

Like everything on the internet you dont know what to believe sometime.

Thanks for your replies

Mat

• Hi Charlie, Michael Baker Jr. wanted to send me to that part of the world,but also to Saudi Arabia,South America,and this is when the Alaska Pipeline was being built,they wanted me to go work on it also. So i studied how to do a star shot on the Southern Cross for the South Pole, for New Zealand.I made plans to go and my mother became very sick ,so i change my plans and stayed in the U.S.But that's life.Everyone surveys the same,about their system. they have their own projections for this area the old system was done for sailors.That's why i gave Mat the New Zealand Site,there is a lot of info on this site about New Zealand and there controls,since he is a student i thought this would help him, go there and look at it.I found it about a year ago ,looking for Datum conversion,Back to the hunting they have a special Deer , a Stag similar to North American Elk. these Deer came from Europe, I forgot the date but it real old.they are more impresses than our Elk, much larger and there racks also, in fact this help save this Deer from extinction, but now it become even bigger in New Zealand over the years of living there. I was in hopes i would get to hunt one if i went. So Mat take all this in and know that you have new friends in the Survey World and we are here to help you.

• Hey Billy

around the 1850 british red deer (Cervus elaphus) were released into New Zealand. They cause some destruction to the native plants in the high country. in the 1930 they culled of 1000 of them. Numbers are getting up there again now and you do see some large stags being brought out. i live on the west coast of the south island where the deer can be found everywhere.

Thanks for all the information and help guys really appreciate it

• 1. What is scale coefficient?

In New Zealand, the official datum is New Zealand Geodetic Datum 2000 (NZGD2000), as you can check on DATUM, and the official Projection is New Zealand Transverse Mercator 2000, as you can check on Projection.

UTM projection is a projection system that was designed for sailing, so the angles on the real life and on drawings are the same, but, the distances are not the same. In order to match, it is required to apply a scale coefficient (factor scale) that depend on your coordinates and the coordinates of the target.

2. what is scale error

Scale error is the error that you have when you apply a scale. As our visual accuracy is 0.2 mm, on any drawing, your scale error will be 0.2mm x Scale. For example, in a 1:10000 scale, the error scale is 0.2mm x 10000 = 2000 mm = 2 m. So it is useless any survey with 2 points within 2 meters, as there won´t be any representation for it. For digital purposes, it is the same issue.

Regarding height, it is something similar but regarding level curves. For example, usually, on a 1:10000 scale, the curve levels are within 1 meter, so any element that has less than 1 meter in height won´t have any representation on drawings.

You should consider this issue in order to know the accuracy on drawings. So, for example, if your are doing a survey for a 1:10000 scale drawings, you shouldn´t waste your time take details that have less than 2 meters on plan and less than 1 meter on height. If you take a survey of one road, you shoul take the axis and the end of the paved/unpaved shoulder. The remaining details should be done by CAD systems, as on scale, it doesn´t have representation. The kerbs have no representation, so 1 point is enough for surveying, if one staircase is minor than 2 meters, you shoudn´t represent it...

3. what is grid scale constant

A grid scale constant can be many issues, but usually, it is mention for:

- on UTM (Mercator) projections, it is the grid area when you can consider a factor scale as constant.

- on normal surveying, it is a grid when you are considering the factor scale constant (usually 1.0), so you don´t need to apply factor scale.

Which one do you think are you interested?

• Thanks for being a mate David,that's what this is all about helping surveyors of the World.

• Hey Mate, How is it down under , i like to take a look at that Southern Cross myself. Worked with a Civil Eng / Surveyor  from New Zealand ,here in Texas he was a blast told me many things about New Zealand, he told me dinosaurs were only 6000 years old,Like i said he was a blast. Where do you live,i like to hunt those Stag bucks. Anyway here is some more info  and this New Zealand site there is a lot of links and information there that can help you i have even used it, plus some more like survenator gave you. so good day mate. stay in touch Mat.

billy,  I see you live in Hokitika

http://www.linz.govt.nz/data/geodetic-services/coordinate-conversion

https://en.wikipedia.org/wiki/Mercator_projection

https://en.wikipedia.org/wiki/Lambert_conformal_conic_projection

https://en.wikipedia.org/wiki/Lambert_azimuthal_equal-area_projection

https://en.wikipedia.org/wiki/Lambert_projection

https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordin...

• You need to understand the basics of State Plane Coordinates & geodetic science. Your best source of information is probably free. Contact your States geodetic survey & NGS. Geodesy is a complicated subject & there is no easy solution so expect to do some work. If there is an easy "cook book" formula, I haven't found it. If you are a registered surveyor, it is not beyond your capabilities but a transit or rectilinear survey is different than a geodetic survey that takes the scale factors & mapping angle into account. I am no expert on the subject but that is my take thus far.
• Party Chief
Coefficient
In mathematics, a coefficient is a multiplicative factor in some term of a polynomial, a series, or any expression; it is usually a number, but may b…
This reply was deleted.