# Project Georeferencing

## Coordinate Systems in SpatialExplorer 6

### How Datums, Epochs and Projected Coordinate Systems are handled in SpatialExplorer 6 Desktop

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If you experience outputs of SpatialExplorer being shifted by up to tens of meters, ensure that the epoch of imported and exported data is correct.
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All data that is active in SpatialExplorer is georeferenced based on the project's (.plp file) datum. To ensure that your end products are correctly generated it is critical to understand how and when transformations are applied during data import and data export.

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It is highly advisable to utilize the same datum & epoch for input, intermediate, and output data.
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Currently SpatialExplorer supports time dependent datum transformations that are based on the input source's specified epoch. It does not support time dependent transforms with a user specified target epoch.
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* **Input data**: The coordinate reference system information must be known by the user for all input data. 
  * SpatialExplorer will automatically read metadata and also potentially prompt the user if information cannot be found during import. 
  * SpatialExplorer will transform all input data to geocentric coordinates based on the project's datum and the specified input data's datum & epoch using a time dependent datum transformation.
* **Active Data**: All data that is actively displayed in SE will be based on the project's datum & the epoch of inputs. 
  * The project (.plp) datum & epoch should be set to match the user's desired coordinate system for their final products.
  * The project epoch should always be set to match that of your input files.
* **Output Data**: The user can specify which coordinate reference system to use when outputting data. 
  *  The SpatialExplorer project epoch will be used as input to the final transformation, so it must match your intended target CRS.
  * Output's CRS should match the project datum to avoid unnecessary transformations. 

![](/files/-MZyEZW1pm969lUjACfr)

## How to ensure accurate Georeferencing in SpatialExplorer

![](/files/-MZxpITDM_yTRztw2A0k)

![](/files/-M_S3YnII5hfltUbVzq4)

1. Open your .plp and set the datum & epoch in SpatialExplorer. Current project settings are visible in the top right corner. These settings are saved in your .plp file. Change inappropriate settings by clicking the datum & epoch label in the top right  corner of SE. This requires a save & re-launch of your project.
2. Import processed trajectory files and specify the datum & epoch used during their creation. SpatialExplorer will prompt the user for what information is needed depending on the file format.
3. Import GCP files and specify their projection, datum and epoch.
4. Proceed with the next stages in your SpatialExplorer workflow.
5. Export products using your desired projected coordinate reference system.

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