I am working in a project that involve several countries. I am base in the middle of the project, the engineering department receive a KMZ file with all the information we need for site, so we convert that KMZ file in SHP files and worked with that inform

[PatriciaDianderas]

need help!!!

[JoeBorgione]

Not real sure what you are asking for; perhaps you could be a little more descriptive.

[PatriciaDianderas]

Ok, I will try to explain better my problem.

The original shapes where created in WGS 1984, I do not know why at the moment to share the projection coordinates were changed, so now I have shp files in a server that are in the Projection Coordinate System WGS_1984_Web_Mercator_Auxiliary_Sphere (use in google earth etc), but I have to work with that information in the Greek Grid.

When I transform the server shp files to the Greek Grid I have a difference in the position with the original information:

1st I use ArcToolbox/projections for made the transformations and obtain a difference in the in the coordinates with the original shapes,

2nd so I try by other way and export the server shp files using the same coordinate system as the data frame (Greek Grid) and in again obtain the same coordinates, means all are move from the original shapes.

If during all these different process we use ArcGIS 10.3 why we have difference in the information? it is possible that any of the parameters in ArcGIS could be wrong?

I am trying to find the parameters of the transformation between WGS_1984_Web_Mercator_Auxiliary_Sphere and Greek Grid so maybe creating a custom geographic transformation I can obtain the correct coordinates.

Can somebody help me?

[JoeBorgione]

I'm going to reach out to Melita Kennedy​ as she is the person best qualified to answer this one.

[MelitaKennedy]

Hello Patricia,

Is the data using the GGRS87 Greek Grid or the older "Greek" datum/GeogCRS / Hatt projection?

Are you setting any transformations? The most accurate transformations between the older Greek Grid (Hatt projection) and GGRS87 Greek Grid is a polynomial transformation that you would have to get from the government but Esri doesn't support polynomial transformations anyway.

We have a Greek datum/GeogCRS to GGRS87 transformation in version 10.0. There's also a GGRS87 to WGS84 transformation.

If you haven't been, trying setting the corresponding transformation in ArcMap (data frame properties, Coordinate Systems tab, Transformations button).

Melita

[PatriciaDianderas]

HI Melita,

The official parameters that they gave me are:

GEODETIC PARAMETERS

GREECE Grid

Projection: Traverse Mercator

False Easting:500000.0

False Northing:  0.0

Central Meridian:  24.0

Scale Factor:  0.9996

Latitude Of Origin:  0.0

Linear Unit:  Meter (1,0)

Geographic Coordinate System: GCS GGRS 1987

Angular Unit:  Degree (0,0174532925199433)

Prime Meridian:  Greenwich (0,0)

Datum:  D GGRS 1987

Spheroid: GRS 1980

Semimajor Axis:  6378137.0

Semiminor Axis:  6356752,314140356

Inverse Flattening:  298.257222101

But when I found the differences after the transformation, a college working in other area near the one I am, told me that they solve the problem using this:

Transformation Method: Coordinate Frame

dx=-203; dy=73;dz=243

rx=0,17;ry=0,06;rz=0,151;s=0,294

So I am trying to find from where they obtain these parameters but until now no answer.

I am still lost, and could not explain the difference, all of us are using ArcGIS 10.3

thanks is advance.

cheers

Patricia

[PatriciaDianderas]

Melita,

what I use to do is import the data from the server (that is in WGS_1984_Web_Mercator_Auxiliary_Sphere) then I use the projections and transformation's tool from ArcToolbox, when I introduce the Input dataset or feature class, it automatically recognize de projection(WGS_1984_Web_Mercator_Auxiliary_Sphere) and then I set the out coordinate system in greed grid with the parameters:

Greek_Grid
WKID: 2100 Authority: EPSG

Projection: Transverse_Mercator
False_Easting: 500000.0
False_Northing: 0.0
Central_Meridian: 24.0
Scale_Factor: 0.9996
Latitude_Of_Origin: 0.0
Linear Unit: Meter (1.0)

Geographic Coordinate System: GCS_GGRS_1987
Angular Unit: Degree (0.0174532925199433)
Prime Meridian: Greenwich (0.0)
Datum: D_GGRS_1987
  Spheroid: GRS_1980
    Semimajor Axis: 6378137.0
    Semiminor Axis: 6356752.314140356
    Inverse Flattening: 298.257222101

and as you can see is the same as the official parameters that the company gave us, and I do not change anything, I do not introduce any information all is done in the program, maybe I am doing wrong and need to know what is that

I hope that with this information you can help me,

cheers

Pat

[MelitaKennedy]

Hi Pat,

I have no official knowledge of those transformation parameters. They're not in the EPSG Geodetic Parameter Dataset, but they are similar to what's there (dx: -199.87, dy:74.79, dz:246.62).

So, try this. In ArcMap, open data frame properties and select the Coordinate Systems tab.

Click the Transformations button.

The "Into:" box should say GGRS 1987. The "From" box should list both GGRS 1987 and WGS 1984. Select WGS 1984.

Click the "Using:" pull-down and select GGRS_1987_To_WGS_1984.

What we're seeing is if that gets rid of most of the offset. If it does, and you're happy with the results, you can stop. If you want to try the 7 parameter transformation that you received, open the Create Custom Geographic Transformation tool in ArcToolbox.

1. Give the new transformation a name like, GGRS 1987 to WGS84 7par

2. Set the source/input GCS to GGRS 1987.

3. Set the target/output GCS to WGS 1984.

4. Set the method to Position Vector (it could also be Coordinate Frame; try PV first as it's more common in Europe).

5. Fill in the parameter values.

6. Okay the dialog.

A transformation-name.gtf file will be created and written to your data location. For example on Windows 7, mine is at C:\Users\<username>\AppData\Roaming\ESRI\Desktop10.4\ArcToolbox\CustomTransformations. You can copy that file between machines but it has to go into the same location (per user).

Melita

[PatriciaDianderas]

Hi Melita,

Apologize for answer quite
late.

Look I try many ways and obtain the same result, well I did not use the parameters that they gave me (which we do not know from where it was obtain) not feel conformable using them; however we travelled to meet the originator of the shape files.

They are working with a huge amount of information, the point is, that they are working and generating the information in Greek GRID, ALL the information; and then they load it in the server. The quantity information for the server they have is too much, so what the IT department did is "block" the volume of the information we can access though internet: for example in the shp file named as Parcels Zone A, it has more than 10000 features inside, then I open the shape file with my computer I can see the complete shape in the screen but when I open attribute table I am capable only to read 1000 items, if I exported the shape only the 1000 items are exported and they are the 1st 1000 items, I can not access to the other 9000 or selected the part I need, only see them in the screen.

So, we saw the original files load in the server (they are in Greek Grid) but immediately when I access to the server (by internet in the web portal) I only have real access of part of the shape, and when I check the layer properties the project
system coordinate is changed to WGS_1984_Web_Mercator_Auxiliar_Sphere!!!!

Therefore is it possible that when the information is load to the server and access to it through the web the files coordinate system change?

Or maybe because the files are (we can say) split to have access only the 1000 items first contributed to change the coordinates and increase the mistake in the accuracy?

I really do not know what to do, and how explain to my boss why we have that difference.

cheers

Pat