# writers.ept_addon¶

The EPT Addon Writer supports writing additional dimensions to Entwine Point Tile datasets. The EPT addon writer may only be used in a pipeline with an EPT reader, and it creates additional attributes for an existing dataset rather than creating a brand new one.

The addon dimensions created by this writer are stored independently from the corresponding EPT dataset, therefore write-access to the EPT resource itself is not required to create and use addon dimensions.

Default Embedded Stage

This stage is enabled by default

## Example¶

This example downloads the Autzen dataset (10M points) and runs the :ref:filters.smrf <SMRF filter>_, which populates the Classification dimension with ground values, and writes the resulting attribute to an EPT addon dataset on the local filesystem.

[{
"type": "readers.ept",
"filename": "http://na.entwine.io/autzen/ept.json"
}, {
"type": "filters.assign",
"assignment": "Classification[:]=0"
}, {
"type": "filters.smrf"
}, {
"type": "writers.ept_addon",
"addons": { "~/entwine/addons/autzen/smrf": "Classification" }
}]


And here is a follow-up example of reading this dataset with the :ref:readers.ept <EPT reader>_ - with the created addon overwriting the Classification value - and then writing the output to a single file with the :ref:writers.las <LAS writer>_.

[{
"type": "readers.ept",
"filename": "http://na.entwine.io/autzen/ept.json",
"addons": { "Classification": "~/entwine/addons/autzen/smrf" }
}, {
"type": "writers.las",
"filename": "autzen-ept-smrf.las"
}]


Here is an example of using multiple mappings in the addons option, to apply a new color scheme with filters.colorinterp mapping the Red, Green, and Blue dimensions to new values.

[{
"type": "readers.ept",
"filename": "http://na.entwine.io/autzen/ept.json"
}, {
"type": "filters.colorinterp"
}, {
"type": "writers.ept_addon",
"addons": {
"~/entwine/addons/autzen/interp/Red":   "Red",
"~/entwine/addons/autzen/interp/Green": "Green",
"~/entwine/addons/autzen/interp/Blue":  "Blue"
}
}]


And to read the data with the new colors:

[{
"type": "readers.ept",
"filename": "http://na.entwine.io/autzen/ept.json",
"addons": {
"Red":   "~/entwine/addons/autzen/interp/Red",
"Green": "~/entwine/addons/autzen/interp/Green",
"Blue":  "~/entwine/addons/autzen/interp/Blue"
}
}, {
"type": "writers.las",
"filename": "autzen-ept-interp.las"
}]


## Options¶

addons
A JSON object whose keys represent output paths for each addon dimension, and whose corresponding values represent the attributes to be written to these addon dimensions. [Required]

Note

The addons option is reversed between the EPT reader and addon-writer: in each case, the right-hand side represents an assignment to the left-hand side. In the writer, the dimension value is assigned to an addon path. In the reader, the addon path is assigned to a dimension.

threads
Number of worker threads used to write EPT addon data. A minimum of 4 will be used no matter what value is specified.