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How to correct Control points Coordinates

i have 2 control points created by GPS on my new project, and my Total station without Scale factor (Leica 407)

So, the Orientation get 16 cm difference

What should i Do?

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Replies to This Discussion

First point... GPS ALWAYS works on WGS84. The only issue you can do is to transform those coordinates to whatever system you are interested.

Second Point, making a projection with a GIS means... nothing? Depends of which projection are you interested in... (Projection is not the correct word, it is only for geometry, for us it is a transformation)

I will put an example... You made your observations with GPS, and then you have used your GIS software to transform it on some other system, for example, UTM. If you are using UTM, this system have always a factor scale, so whatever you are designing, will have a factor scale in our ground.

If you want to use GPS and TS data without taking care of a factor scale, you should setup your GIS software for the Datum you are interested in, the coordinates system you are interested in and a factor scale = 1.0000000. Then, you can use data from one or another source.

But keep in mind that in order to make this transformation, GIS software won´t do that, because they have implemented global transformations as UTM, for example, so it is required to place some benchmarks with global coordinates and no factor scale, and force to your GIS software to make a transformation between the global coordinates without factor scale to your GPS Data.

Clear example... You need to survey an area when you can make some observations with GPS and some observations with TS. So first of all you should place some benchmarks and observe it without factor scale (It means, forget your GPS and use your TS to bring non-factor scale coordinates). Once that you have that coordinates, the observ that benchmarks with your GPS and force your GPS to make a transformation between WGS84 to your local system without factor scale. Once that you have it, you can use GPS or TS freely.

But if you have made your GPS observations, you have transform it with any GIS system, then you got a projected coordinates that USUALLY will have a factor scale. So if you are using a TS upon this data, you will get some closing errors. If that points are very closed, it will seem that it is an instrumental error, but if they are very far, you will have huge errors... Depends on the projection you are using in your GIS system and your position in the projection area.

hello sir I have two gps wgs84 coordinate with scale factor of0.9996 how can I convert it to local coordinates with scale factor of 1

Dear Raymond...

Is not as simple as this.

WGS84 is just a elipsoid, so you have Lat and Long, not X&Y.

In order to get there you need a Datum and a Projection.

Which Datum are you using? (Maybe Umm Er Rus Datum, Midra Jinubi Alignment, Clark 1866)

Which Projection are you using? (ARAMCO Gauss-Krüger Transverse Mercator?)

With these data, we can know how to transform Lat/Long to X/Y, and later we can talk regarding factor scale. If you can provide me those data, we will manage

sir but the client gived me two xy coordinates and they told me this is wgs 84 coordinate 37q zone with scale factor of0.9996

Dear Raymond:

Take a look to https://en.wikipedia.org/wiki/World_Geodetic_System and you will see that there are no coordinates on WGS84.

But your client told you that you are on zone 37q, so you are using an UTM system (take a look at https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordin...) and you are in Saudi Arabia.

In Saudi Arabia, the oficial Datum is Umm Er Rus, with Midra Jinubi Alignment using Clark 1866 elipsoid (not WGS84). The official projection in Saudi Arabia is ARAMCO Gauss-Krüger Tranverse Mercator.

Please, ask to your client if they have used this Datum and Projection and then we will bring new coordinates.

Regards

Means is it a utm coordinate sir....
Is utm is a cartesian coordinate system

UTM is a projection system. It is cartesian but every single point has a different factor scale. Please, send me a sketch of what you have an will give you and idea.

yes it's really useful

hello  Amhed, i am DONE!!

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