# USGS Pluto Relief

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## Usage

You access the global New Horizon relief grid by specifying the special name

> @pluto_relief[\_*rru*[\_*reg*]]

This grid contains observed relief measured via altimetry.
The following codes for the optional *rru* and *reg* are supported (dimensions are listed
for pixel-registered grids; gridline-registered grids increment dimensions by one):

(tbl-pluto_relief)=

| Code | Dimensions    | Reg | Size   | Description                                    |
| ---- | ------------- | --- | ------ | ---------------------------------------------- |
| 01d  | 360 x 180     | g,p | 71 KB  | 1 arc degree Pluto relief (NH @ 59 km)         |
| 30m  | 720 x 360     | g,p | 220 KB | 30 arc minute Pluto relief (NH @ 29 km)        |
| 20m  | 1080 x 540    | g,p | 452 KB | 20 arc minute Pluto relief (NH @ 20 km)        |
| 15m  | 1440 x 720    | g,p | 774 KB | 15 arc minute Pluto relief (NH @ 15 km)        |
| 10m  | 2160 x 1080   | g,p | 1.6 MB | 10 arc minute Pluto relief (NH @ 9.8 km)       |
| 06m  | 3600 x 1800   | g,p | 4.2 MB | 6 arc minute Pluto relief (NH @ 5.9 km)        |
| 05m  | 4320 x 2160   | g,p | 6.0 MB | 5 arc minute Pluto relief (NH @ 4.9 km)        |
| 04m  | 5400 x 2700   | g,p | 9.0 MB | 4 arc minute Pluto relief (NH @ 3.3 km)        |
| 03m  | 7200 x 3600   | g,p | 15 MB  | 3 arc minute Pluto relief (NH @ 2.9 km)        |
| 02m  | 10800 x 5400  | g,p | 33 MB  | 2 arc minute Pluto relief (NH @ 2.0 km)        |
| 01m  | 21600 x 10800 | g,p | 122 MB | 1 arc minute Pluto relief (NH @ 1.0 km)        |
| 52s  | 24888 x 12444 | p   | 124 MB | 52.07... arc second Pluto relief (NH original) |

Note that resolutions 05m and higher are tiled.
See {gmt-docs}`Remote Datasets <datasets/remote-data.html>` for more information.

See {gmt-docs}`GMT remote dataset usage <datasets/remote-data.html#usage>` for when resolution codes are optional or required.
All of these data will, when downloaded, be placed in your ~/.gmt/server directory, with
the pluto_relief files being placed in an `pluto/pluto_relief` sub-directory. If you
do not specify a CPT then the default CPT for this dataset (the GMT master *@pluto_relief.cpt* CPT) will be used.

## Examples

To create a PDF map of the Pluto New Horizons relief at 1 arc degree resolution, try:

```bash
gmt grdimage @pluto_relief_01d -Baf -pdf pluto_relief
```

## Technical Information

As you see, the 01m and lower resolutions are all derivatives of USGS' 52.0732883317 arc-second Pluto_NewHorizons_Global_DEM_300m_Jul2017_16bit.tif
(Moore_et_al., 2016). We have downsampled it via Cartesian Gaussian filtering to prevent
aliasing while preserving the latitude-dependent resolution in the original 52.0732883317 arc sec grid.
The full (6 sigma) filter-widths are indicated in parenthesis. Almost all grids
are available in both gridline- and pixel-registered formats except the original pixel-registered
grid at 52.0732883317 arc-seconds resolution (here called @pluto_relief_52s).

We also scale and reformat the original data to take up very little space so that downloads
from the servers are as fast as possible. For the pluto_relief grids this means we chose 0.25
meter as the grid z step, which is well below the uncertainties in the data. Elevations
are scaled and shifted to fit in a short integer grid that is highly compressed by netCDF
lossless compression and chunking.

**Note**: Because of this quantization, these grids should be used with care in morphometric
studies (e.g., slope, curvature or roughness analyses), since even sub-meter rounding can bias
slope and aspect calculations [Carter, 1992]. We suggest using the original dataset instead for
such applications.

## Data References

1. Carter, J.R., 1992: [<https://doi.org/10.3138/aj35-34h3-524k-0685>].
1. NH: [<https://doi.org/10.1126/science.aad7055>].