Local Coordinates
Alteia has the possibilities to have a Local Coordinates system.
Local Coordinates is a coordinates system that which are localized to minimize visual distortion / simplify measurement in a small region. It is specially good to make measurement and designed to be adapted for a particular region.
Please consult the CRS article if needed.
Alteia Local coordinates is based on a transformation with the help of GCPs from WGS84 Datum to the desired local coordinates.
Consequently those Ground Control Point has to be measured with the wished local coordinates and also in WGS84 (long, lag) DATUM.
1. Workflow
Local coordinates can be specified during the site creation.
Step 1: Click on create a Site
Step 2: In the Site properties, please choose the global site CRS.
Step 3: After choosing your global site CRS please click on Define Local CRS
There are three ways to define the Local CRS:
- Single local-global coordinates file (.csv)
- Separate local and global coordinates files (.csv)
- JXL file
IMPORTANT
- The global coordinates, mentioned here, does not correspond to the GLOBAL SITE CRS. It correspond to the reference for the transformation. And it must be in WGS84 (EPSG:4326). The GLOBAL SITE CRS refers to the system you are using on the platform.
- DO NOT forget to choose the unit in which the local coordinate is written
You can find below example files :
Single Local global Control point.csv
1.1 Single local-global coordinates csv file
It allows the user to embed on a same CSV file, for a given point on the earth the correlation between a global system and a local system.
This CSV file must respect the following rules :
- No Header
- Must contain at least 3 points
- Supported separator must be ,
- Global coordinates of the GCP must be in WGS84 (EPSG:4326)
- Must have the following structure as shown in the example table below (The column must have the same order (first local coordinates followed by the WGS84 coordinates)) :
GCP ID Northing or Y axes (local units) Easting or X axes (local units) Elevation (local units) Latitude (deg) Longitude (deg) Ellipsoid Height (m) gcp 0 9951.901 11728.371 788.614 34.71285 -118.13166 677.058928
gcp 1 9864.197 11796.451 790.885 34.71261 -118.13143 679.331512 gcp 2 9793.678 11671.38 787.715 34.71242 -118.13185 676.168511
gcp 3 9887.278 11570.888 788.415 34.71267 -118.13218 676.866717
1.2 Separate local and global coordinates files (.csv)
- No Header
- Must contain at least 3 points
- Supported separator must be ,
- Global coordinates of the GCP must be in WGS84 (EPSG:4326)
- Must have the following structure as shown in the example table below (The column must have the same order (first local coordinates
followed by the WGS84 coordinates)) :
GCP Global CRS csv :
GCP Local CRS csv :GCP ID Longitude (deg) Latitude (deg) Ellipsoid Height (m) gcp 0 -118.13166 34.71285 677.058928 gcp 1 -118.13143 34.71261 679.331512 gcp 2 -118.13185 34.71242 676.168511 gcp 3 -118.13218 34.71267 676.866717 GCP ID Easting or X axes (local units) Northing or Y axes (local units)
Elevation (local units) gcp 0 11728.371 9951.901 788.614 gcp 1 11796.451 9864.197 790.885 gcp 2 11671.38 9793.678 787.715 gcp 3 11570.888 9887.278 788.415
1.3 JXL file
Supported Projection :
| Projection | Supported by Trimble | Supported by Alteia |
| Mercator |  |
beta |
| Transverse Mercator |  |
 |
| UTM |  |
beta |
| Lambert Conformal Conical |  |
beta |
| Oblique Mercator |  |
|
| Oblique Conformal Cylindrical |  |
|
| Oblique Stereographic |  |
|
| Polar Stereographic |  |
|
| RD Stereographic |  |
|
| Albers Equal Area |  |
beta |
| Cassini Soldner |  |
beta |
| Krovak |  |
|
| New Zealand Map Grid |  |
beta |
| United Kingdom National Grid |  |
|
| Denmark |  |
|
| Hungarian EOV |  |
|
| Stereographic Double |  |
|
| Rectified Skewed Orthomorphic (RSO |  |
|
| UPS North |  |
beta |
| UPS South |  |
beta |
| Projection Grid |  |
Supported Datum Transformation :
| Projection | Supported by Trimble | Supported by Alteia |
| No Datum |  |
 |
| Helmert Three Parameters |  |
beta |
| Helmert Seven Parameters |  |
beta |
| Grid Datum |  |
|
| RTCM Grid |  |
|
Supported Geoid Model :
| Trimble Name | Proj4 filename | Supported |
| EGM96 (Global) | egm96_15.gtx |  |
| GEOID12A (Conus) | g2012au0.gtx |  |
| GEOID12A (Alaska) | g2012aa0.gtx |  |
| GEOID12A (American Samoa) | g2012as0.gtx |  |
| GEOID12A (Guam) | g2012ag0.gtx |  |
| GEOID12A (Hawaii) | g2012ah0.gtx |  |
| GEOID12A (Puerto Rico) | g2012ap0.gtx |  |
| GEOID12B (Conus) | g2012bu0.gtx |  |
| GEOID12B (Alaska) | g2012ba0.gtx |  |
| GEOID12B (American Samoa) | g2012bs0.gtx |  |
| GEOID12B (Guam) | g2012bg0.gtx |  |
| GEOID12B (Hawaii) | g2012bh0.gtx |  |
| GEOID12B (Puerto Rico) | g2012bp0.gtx |  |
| Atlantic Canada HT2 | HT2_0.gtx |  |
2. Update the local CRS of an already existing site
It is possible to define the local CRS of a site from the info panel
In order to make the transformation possible, a global system must be defined previously
With this method we enabled the capacity to export older dataset into the local system as we now have the transformation with both systems.
3. Set the Local coordinates during Site Creation with images
If you create a site and upload images at the same time, you can also set the local coordinate :
Like mentioned above, the global site Coordinate Reference System must be also defined.
4. Data importation in local CRS
- Vector : User can upload a vector file with the local CRS.
- Raster : For the moment a raster file can only be uploaded as File in local CRS which means it will not be displayed on the map.
- Point Cloud : Not supported yet in Local CRS
5. Data exportation in local CRS
Datasets can be export in Local CRS. Please click here to learn about exporting data on Alteia
In the download section, during the export, click on Switch to Local CRS.
- Vector : users can export in local CRS
- Raster : users can export in local CRS
- Point Cloud : user can export in local CRS using the analytic Convert Point Cloud to local coordinates
