.. index:: ! grdmask .. include:: module_core_purpose.rst_ ******* grdmask ******* |grdmask_purpose| Synopsis -------- .. include:: common_SYN_OPTs.rst_ **gmt grdmask** *table* |-G|\ *outgrid* |SYN_OPT-I| |SYN_OPT-R| [ |-A|\ [**m**\|\ **p**\|\ **x**\|\ **y**\|\ **r**\|\ **t**] ] [ |-C|\ **f**\|\ **l**\|\ **o**\|\ **u** ] [ |-N|\ [**z**\|\ **Z**\|\ **p**\|\ **P**]\ *values* ] [ |-S|\ *radius*\|\ *xlim*\ /*ylim* ] [ |SYN_OPT-V| ] [ |SYN_OPT-a| ] [ |SYN_OPT-bi| ] [ |SYN_OPT-di| ] [ |SYN_OPT-e| ] [ |SYN_OPT-f| ] [ |SYN_OPT-g| ] [ |SYN_OPT-h| ] [ |SYN_OPT-i| ] [ |SYN_OPT-j| ] [ |SYN_OPT-n| ] [ |SYN_OPT-qi| ] [ |SYN_OPT-r| ] [ |SYN_OPT-w| ] [ |SYN_OPT-x| ] [ |SYN_OPT-:| ] [ |SYN_OPT--| ] |No-spaces| Description ----------- **grdmask** can operate in two different modes. 1. It reads one or more *pathfiles* that each define a closed polygon. The nodes defined by the specified region and lattice spacing will be set equal to one of three possible values depending on whether the node is outside, on the polygon perimeter, or inside the polygon, with the assigned *z* value selected via |-N|. If multiple polygons overlap the same nodes then the polygon selected depends on the |-C| selection. The resulting mask may be used in subsequent operations involving :doc:`grdmath` to mask out data from polygonal areas. 2. The *pathfiles* simply represent data point locations and the mask is set to the inside or outside value depending on whether a node is within a maximum distance from the nearest data point. If the distance specified is zero then only the nodes nearest each data point are considered "inside". Required Arguments ------------------ *table* The name of 1 or more ASCII [or binary, see **-bi**] files holding the polygon(s) or data points. .. _-G: .. |Add_outgrid| replace:: Give the name of the output mask grid file. .. include:: /explain_grd_inout.rst_ :start-after: outgrid-syntax-begins :end-before: outgrid-syntax-ends .. _-I: .. include:: explain_-I.rst_ .. |Add_-R| replace:: |Add_-R_links| .. include:: explain_-R.rst_ :start-after: **Syntax** :end-before: **Description** Optional Arguments ------------------ .. _-A: **-A**\ [**m**\|\ **p**\|\ **x**\|\ **y**] If the input data are geographic (as indicated by **-f**) then the sides in the polygons will be approximated by great circle arcs. When using the |-A| sides will be regarded as straight lines. Alternatively, append **m** to have sides first follow meridians, then parallels. Or append **p** to first follow parallels, then meridians. For Cartesian data, points are simply connected, unless you append **x** or **y** to construct stair-case paths whose first move is along *x* or *y*, respectively. If your Cartesian data are polar (*theta*, *r*), append **t** or **r** to construct stair-case paths whose first move is along *theta* or *r*, respectively. .. _-C: **-C**\ **f**\|\ **l**\|\ **o**\|\ **u** Clobber mode: Selects the polygon whose *z*-value will determine the grid nodes. Choose from the following modes: **f** for the first polygon to overlap a node; **o** for the last polygon to overlap a node; **l** for the polygon with the lowest *z*-value, and **u** for the polygon with the uppermost *z*-value [Default is **o**]. **Note**: Does not apply to |-S|. For polygon *z*-values, see |-N|. .. _-N: **-N**\ [**z**\|\ **Z**\|\ **p**\|\ **P**]\ *values* Sets the *out/edge/in* that will be assigned to nodes that are *out*\ side the polygons, on the *edge*, or *in*\ side. Values can be any number, including the textstring NaN [Default is 0/0/1]. Optionally, use **Nz** to set polygon insides to the z-value obtained from the data (either segment header **-Z**\ *zval*, **-L**\ *header* or via **-a**\ Z=\ *name*); use **-NZ** to consider the polygon boundary as part of the inside. Alternatively, use **-Np** to use a running number as polygon ID; optionally append start of the sequence [0]. Here, **-NP** includes the polygon perimeter as inside. **Note**: **-N**\ **z**\|\ **Z**\|\ **p**\|\ **P** cannot be used in conjunction with **-S**; they also all optionally accept /*out* [0]. .. _-S: **-S**\ *radius*\|\ *xlim*\ /*ylim* Set nodes to inside, on edge, or outside depending on their distance to the nearest data point. Nodes within the searsch *radius* [0] from the nearest data point are considered inside; append a distance unit (see `Units`_). If *radius* is given as **z** then we instead read individual radii from the 3rd input column. Unless Cartesian data, specify the unit of these radii by appending it after **-Sz**. If |-S| is not set then we consider the input data to define one or more closed polygon(s) instead. For Cartesian data with different units you can instead append *xlim*\ /*ylim* which will perform a rectangular search where all nodes within ±\ *xlim* and ±\ *ylim* of a data point will be considered inside. One can also achieve the rectangular selection effect by using the **-S**\ *n_cells*\ **c** form. Here *n_cells* means the number of cells around each data point. As an example, **-S**\ 0\ **c** means that only the cell where point lies is masked, **-S**\ 1\ **c** masks one cell beyond that (i.e. makes a 3x3 neighborhood), and so on. .. |Add_-V| replace:: |Add_-V_links| .. include:: explain_-V.rst_ :start-after: **Syntax** :end-before: **Description** .. include:: explain_-aspatial.rst_ .. |Add_-bi| replace:: [Default is 2 input columns (3 with **-Sz**)]. .. include:: explain_-bi.rst_ .. |Add_-di| unicode:: 0x20 .. just an invisible code .. include:: explain_-di.rst_ .. |Add_-e| unicode:: 0x20 .. just an invisible code .. include:: explain_-e.rst_ .. |Add_-f| unicode:: 0x20 .. just an invisible code .. include:: explain_-f.rst_ .. |Add_-g| unicode:: 0x20 .. just an invisible code .. include:: explain_-g.rst_ .. |Add_-h| unicode:: 0x20 .. just an invisible code .. include:: explain_-h.rst_ .. include:: explain_-icols.rst_ .. include:: explain_distcalc.rst_ **-n**\ [**b**\|\ **c**\|\ **l**\|\ **n**][**+a**][**+b**\ *BC*][**+t**\ *threshold*] Append **+b**\ *BC* to set any boundary conditions to be used, adding **g** for geographic, **p** for periodic, or **n** for natural boundary conditions. For the latter two you may append **x** or **y** to specify just one direction, otherwise both are assumed. [Default is geographic if grid is geographic]. .. include:: explain_-qi.rst_ .. |Add_nodereg| unicode:: 0x20 .. just an invisible code .. include:: explain_nodereg.rst_ .. include:: explain_-w.rst_ .. include:: explain_core.rst_ .. include:: explain_help.rst_ .. include:: explain_distunits.rst_ .. include:: explain_grd_coord.rst_ .. include:: explain_inside.rst_ Notes ----- A grid produced by grdmask is a *categorical* dataset. As such, one has to be careful not to interpolate it with standard methods, such as splines. However, if you make a map of this grid using a map projection the grid will be reprojected to yield a rectangular matrix in the projected coordinates. This interpolation is done using splines by default and thus may yield artifacts in your map. We recommend you use :doc:`grdimage` **-nn** to instead use a nearest neighbor interpolation for such cases. Save storage space ------------------ Since most uses of grdmask revolves around creating mask grids that hold just a few integer values (and perhaps NaN), we choose to write them to disk as byte grids by appending the suffix **=nb** to the desired grid filename. Some situations may store integers that exceed the range available in a byte and for those we specify a short integer grid with **=ns**. For larger integers you may consider **=ni**, otherwise use the default float grid format. Examples -------- .. include:: explain_example.rst_ To set all nodes inside and on the polygons coastline_*.xy to 0, and outside points to 1, do :: gmt grdmask coastline_*.xy -R-60/-40/-40/-30 -I5m -N1/0/0 -Gland_mask.nc=nb -V To set nodes within 50 km of data points to 1 and other nodes to NaN, do :: gmt grdmask data.xyz -R-60/-40/-40/-30 -I5m -NNaN/1/1 -S50k -Gdata_mask.nc=nb -V To assign polygon IDs to the gridnodes using the insides of the polygons in plates.gmt, based on the attribute POL_ID, do :: gmt grdmask plates.gmt -R-40/40/-40/40 -I2m -Nz -Gplate_IDs.nc=ns -aZ=POL_ID -V Same exercise, but instead compute running polygon IDs starting at 100, do :: gmt grdmask plates.gmt -R-40/40/-40/40 -I2m -Np100 -Gplate_IDs.nc=ns -V See Also -------- :doc:`gmt`, :doc:`grdlandmask`, :doc:`grdmath`, :doc:`grdclip`, :doc:`mask`, :doc:`clip`