# NASA Mars Relief :::{figure} /_static/nasa-logo-web-rgb.png :align: right :scale: 20 % ::: :::{figure} /_static/GMT_mars_relief.jpg :height: 888 px :width: 1774 px :align: center :scale: 40 % ::: ## Usage You access the global MOLA relief grid by specifying the special name > @mars_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-mars_relief)= | Code | Dimensions | Reg | Size | Description | | ---- | -------------- | --- | ------ | ----------------------------------------------- | | 01d | 360 x 180 | g,p | 109 KB | 1 arc degree Mars relief (MOLA @ 168 km) | | 30m | 720 x 360 | g,p | 373 KB | 30 arc minute Mars relief (MOLA @ 84 km) | | 20m | 1080 x 540 | g,p | 781 KB | 20 arc minute Mars relief (MOLA @ 56 km) | | 15m | 1440 x 720 | g,p | 1.3 MB | 15 arc minute Mars relief (MOLA @ 42 km) | | 10m | 2160 x 1080 | g,p | 2.8 MB | 10 arc minute Mars relief (MOLA @ 28 km) | | 06m | 3600 x 1800 | g,p | 7.5 MB | 6 arc minute Mars relief (MOLA @ 17 km) | | 05m | 4320 x 2160 | g,p | 11 MB | 5 arc minute Mars relief (MOLA @ 16 km) | | 04m | 5400 x 2700 | g,p | 16 MB | 4 arc minute Mars relief (MOLA @ 11 km) | | 03m | 7200 x 3600 | g,p | 28 MB | 3 arc minute Mars relief (MOLA @ 8.4 km) | | 02m | 10800 x 5400 | g,p | 61 MB | 2 arc minute Mars relief (MOLA @ 5.6 km) | | 01m | 21600 x 10800 | g,p | 228 MB | 1 arc minute Mars relief (MOLA @ 2.8 km) | | 30s | 43200 x 21600 | g,p | 822 MB | 30 arc second Mars relief (MOLA @ 1.4 km) | | 15s | 86400 x 43200 | g,p | 2.7 GB | 15 arc second Mars relief (MOLA @ 0.7 km) | | 12s | 106694 x 53347 | p | 3.1 GB | 12.14... arc second Mars relief (MOLA original) | Note that resolutions 05m and higher are tiled. See {gmt-docs}`Remote Datasets ` for more information. See {gmt-docs}`GMT remote dataset 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 mars_relief files being placed in an `mars/mars_relief` sub-directory. If you do not specify a CPT then the default CPT for this dataset (the GMT master *@mars_relief.cpt* CPT) will be used. ## Examples To create a PDF map of the Mars MOLA relief at 1 arc degree resolution, try: ```bash gmt grdimage @mars_relief_01d -Baf -pdf mars_relief ``` ## Technical Information As you see, the 01m and lower resolutions are all derivatives of USGS' 12.1468873601 arc-second Mars_HRSC_MOLA_BlendDEM_Global_200mp_v2.tif (Neumann_et_al., 2003). We have downsampled it via Cartesian Gaussian filtering to prevent aliasing while preserving the latitude-dependent resolution in the original 12.1468873601 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 12.1468873601 arc-seconds resolution (here called @mars_relief_12s). 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 mars_relief grids this means we chose 0.5 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: []. 1. MOLA: [].