Any One Can help me,

We have completed the static survey with PM3 for Fixing of Control Poins.after processed we have got Easting Northing with Vector Distance.(UTM/WGS84-Zone43N)

But the problem is the vector distance and the distance calculated from the co ordinates is not matching.The error is increased based on the distance, for Examble if the co ordinate distance is 25m the vector distane is 24.97m if the co ordinate distance is 2657m the vector distance is 2653.when the distance is increaing the error also increase.

But the Vector distance is matching with the Total station distance with out any error. I feel there is some thing which i am missing to change the setup when i am generating the co ordinate by GNSS.

Due to this we have been struck up please anybody can help us to short out this problem

P.K.Samy

would you post a couple of examples of your xyz coordinates and the resulting computed vectors?

JD

The vector distances are surface slope measurements. They should be with 0.01m of your traverse ground measurements. You need to account for the difference in elevation, for which you can use ortho or elliptical for check purposes. Unless you are near sea level (i.e. bellow the ellipsoid) your vector distances should be greater than your grid distances.

You need to use a proper survey grid, which UTM is not, to relate ground measurements to grid measurements. You may have to create one. Where exactly are you, I am in Zone18N whic is a long ways away?

Paul in PA
Modified By Lawrence Paul Lopresti on 10/8/2006 at 10:19 AM

Pythagorous smiles upon you.

Dangerous Dave

I believe Mr. SAMY may be in India as he seemed to suggest in prior posts.

From the University of Wisconsin Green Bay,

http://www.uwgb.edu/dutchs/FieldMethods/UTMSystem.htm

"The Mercator projection is a conformal projection, meaning that angles and small shapes on the globe project as the same angles or shapes on the map. The price paid by all conformal projections is great variation in scale away from the central portions of the map. Greenland on a Mercator map looks as big as South America, though it has actually only 1/8 the area. However, a small portion of the Greenland coast (or any small region, in fact) has the same shape on the map as it does on the ground."

"Within ten degrees or so of the equator, the scale error on a Mercator map is only a percent or so, so in that region a Mercator map is about as accurate as a map can get."

"Because the Transverse Mercator projection is very accurate in narrow zones, it has become the basis for a global coordinate system called the Universal Transverse Mercator System or UTM System. The globe is subdivided into narrow longitude zones, which are projected onto a Transverse Mercator projection. A grid is constructed on the projection, and used to locate points. The upside of the grid system is that, since the grid is rectangular and decimal, it is far easier to use than latitude and longitude. The downside is that, unlike latitude and longitude, there is no way to determine grid locations independently. The scale along the central meridian of each zone is 0.9996 of true scale. True scale occurs about 180 kilometers east and west of the central meridian."

0.9996 is significantly more scale distortion than our SPC systems.

25.00m * 0.9996 = 24.99m

A UTM zone is 668km wide, so at the edges, 334km from the meridian, scale distortion can be significant.

Samy may or may not be in 43N which would put him in the first zone North of the equator. I am not in 18N I am in 18T. Solutions breaks UTM into S & N. But UTM zones run from C through X.

Samy is that zone 43N per UTM or per Solutions?

Paul in PA

Do not use the distances on the vectors tab as a basis for comparison of inverses between coordinates.

GNSS Solutions is not COGO software. The vector lengths are not inverse disances between coordinates.

From all apparent evidence the reported vectors are as recorded on the surface. The only real question is where on the surface?

I had assumed that they might be from the ground point of my observations, because I saw similar vectors when using different antenna heights. But the more I think about, I believe they could also be from ARP to ARP which is where the raw data originates. Since I now use very similar antenna heights, slant height of 6.991' for my ProMark 2s and vertical height of 7.040' from my Z-12 there is no way for me to see the difference.

It might be easier to show if Solutions had an x, y, z coordinate system, but Solutions does give my x, y, z differences for each vector. When I use several Z-12s, I can also compare my OPUS x, y, z values. I have one project where I used 3 Z-12s and 3 PM2s. Since I only have 4 fixed height rod setups, 2 Z-12s were on tripods with different heights. I will go back and compare my OPUS x, y, z positions with my Solutions x, y, z differences.

It is simple geometry, SPC gives me N and E, plus I have an UP value. I have to convert my SPC N & E to a ground N & E but my UP does not change.

The vector distances are not inverses between 3D coordinates, since they are calculated prior to the coordinates. However they give the same vaule as if you did a 3D inverse between the resulting coordinate sets. Solutions is a 3D software while in most COGO packages we consider an inverse as 2D. It is all in your perspective.

Paul in PA

People expect me to tell them why the vector length is not the same as an inverse between the coordinates.

GNSS Solutions is not COGO. That is an opinion from somebody who uses COGO to make inverse calculations.

I have no problem with whatever works for anybody. Use the tools for whatever benefit they provide to you. GNSS Solutions provides many beneficial features related to GPS data processing.

It is not my intention to make the software be something that it is not. GNSS Solutions is not COGO.

I was trying to explain the differences.

BTW Phil, update your email address in your profile.

Paul in PA

I just did a check on data from my Saturday project. I raise one receiver antenna 2m and recalculated. The elevation dropped 2m and the vector got longer to the point that was higher and the vector got shorter to the point that was lower. This tells me that the vectors Solutions reports are slope ground vectors, from ground point to ground point. i.e. Solutions is inversing my N, E and UP position values.

It makes very good sense to me to compare my GPS vectors with my 3D traverse vectors.

Paul in PA
Modified By Lawrence Paul Lopresti on 10/9/2006 at 8:35 PM

My problem is the processed co ordinate distance is not matching with the ground distance i have 1m error for a Km.but that it is matching with Vector distance which is Slope Distance.

PKS