.. index:: ! gmtselect .. include:: module_core_purpose.rst_ ********* gmtselect ********* |gmtselect_purpose| Synopsis -------- .. include:: common_SYN_OPTs.rst_ **gmt select** [ *table* ] [ |SYN_OPT-Area| ] [ |-C|\ *pointfile*\ \|\ *lon*/*lat*\ **+d**\ *dist* ] [ |-D|\ *resolution*\ [**+f**] ] [ |-E|\ [**f**][**n**] ] [ |-F|\ *polygonfile* ] [ |-G|\ *gridmask* ] [ |-I|\ [**cfglrsz**] ] [ |-J|\ *parameters* ] [ |-L|\ *linefile*\ **+d**\ *dist*\ [**+p**] ] [ |-N|\ *maskvalues* ] [ |SYN_OPT-R| ] [ |SYN_OPT-V| ] [ |-Z|\ *min*\ [/*max*]\ [**+a**]\ [**+c**\ *col*]\ [**+h**\ [**k**\|\ **s**]]\ [**+i**] ] [ |SYN_OPT-a| ] [ |SYN_OPT-b| ] [ |SYN_OPT-d| ] [ |SYN_OPT-e| ] [ |SYN_OPT-f| ] [ |SYN_OPT-g| ] [ |SYN_OPT-h| ] [ |SYN_OPT-i| ] [ |SYN_OPT-o| ] [ |SYN_OPT-q| ] [ |SYN_OPT-s| ] [ |SYN_OPT-w| ] [ |SYN_OPT-:| ] [ |SYN_OPT--| ] |No-spaces| Description ----------- **select** is a filter that reads (x, y) or (longitude, latitude) positions from the first 2 columns of *infiles* [or standard input] and uses a combination of 1-7 criteria to pass or reject the records. Records can be selected based on whether or not they are 1) inside a rectangular region (|-R| [and |-J|]), 2) within *dist* km of any point in *pointfile*, 3) within *dist* km of any line in *linefile*, 4) inside one of the polygons in the *polygonfile*, 5) inside geographical features (based on coastlines), 6) has z-values within a given range, or 7) inside bins of a grid mask whose nodes are non-zero. The sense of the tests can be reversed for each of these 7 criteria by using the |-I| option. See option **-:** on how to read (*y, x*) or (*lat, lon*) files (this option affects all module input data). **Note**: If no projection information is used then you must supply **-fg** to tell **select** that your data are geographical. Required Arguments ------------------ .. |Add_intables| unicode:: 0x20 .. just an invisible code .. include:: explain_intables.rst_ Optional Arguments ------------------ .. _-A: .. |Add_-A| replace:: Ignored unless |-N| is set. .. include:: explain_-A.rst_ .. _-C: **-C**\ *pointfile*\ \|\ *lon*/*lat*\ **+d**\ *dist* Pass all records whose location is within *dist* of any of the points in the ASCII file *pointfile*. If *dist* is zero then the 3rd column of *pointfile* must have each point's individual radius of influence. If you only have a single point then you can specify *lon*/*lat* instead of *pointfile*. Distances are Cartesian and in user units; specify **-fg** to indicate spherical distances and append a distance unit, even if the distance specified is 0. (see `Units`_). Alternatively, if |-R| and |-J| are used then geographic coordinates are projected to map coordinates (in cm, inch, or points, as determined by :term:`PROJ_LENGTH_UNIT`) before Cartesian distances are compared to *dist*. .. _-D: **-D**\ *resolution*\ [**+f**] Ignored unless |-N| is set. Selects the resolution of the coastline data set to use ((**f**)ull, (**h**)igh, (**i**)ntermediate, (**l**)ow, or (**c**)rude). The resolution drops off by ~80% between data sets. [Default is **l**]. Append (**+f**) to automatically select a lower resolution should the one requested not be available [abort if not found]. Note that because the coastlines differ in details it is not guaranteed that a point will remain inside [or outside] when a different resolution is selected. .. _-E: **-E**\ [**f**][**n**] Specify how points exactly on a polygon boundary should be considered. By default, such points are considered to be inside the polygon. Append **f** and/or **n** to change this behavior for the |-F| and/or |-N| options, respectively, so that boundary points are considered to be outside. .. _-F: **-F**\ *polygonfile* Pass all records whose location is within one of the closed polygons in the multiple-segment file *polygonfile*. For spherical polygons (*lon, lat*), make sure no consecutive points are separated by 180 degrees or more in longitude. Note that *polygonfile* must be in ASCII regardless of whether **-bi** is used. .. _-G: **-G**\ *gridmask* Pass all locations that are inside the valid data area of the grid *gridmask*. Nodes that are outside are either NaN or zero. .. _-I: **-I**\ [**cflrsz**] Reverses the sense of the test for each of the criteria specified: - **c** - select records **not** inside any point's circle of influence. - **f** - select records **not** inside any of the polygons. - **g** - pass records inside the cells with z equal zero of the grid mask in |-G|. - **l** - select records **not** within the specified distance of any line. - **r** - select records **not** inside the specified rectangular region. - **s** - select records **not** considered inside as specified by |-N| (and |-A|, |-D|). - **z** - select records **not** within the range specified by |-Z|. .. |Add_-J| replace:: |Add_-J_links| .. include:: explain_-J.rst_ :start-after: **Syntax** :end-before: **Description** .. _-L: **-L**\ *linefile*\ **+d**\ *dist*\ [**+p**] Pass all records whose location is within *dist* of any of the line segments in the ASCII multiple-segment file *linefile*. If *dist* is zero then we will scan each sub-header in the *linefile* for an embedded **-D**\ *dist* setting that sets each line's individual distance value. Distances are Cartesian and in user units; specify **-fg** to indicate spherical distances append a distance unit (see `Units`_). Alternatively, if |-R| and |-J| are used then geographic coordinates are projected to map coordinates (in cm, inch, m, or points, as determined by :term:`PROJ_LENGTH_UNIT`) before Cartesian distances are compared to *dist*. Append **+p** to ensure only points whose orthogonal projections onto the nearest line-segment fall within the segment's endpoints [Default considers points "beyond" the line's endpoints]. .. _-N: **-N**\ *maskvalues* Pass all records whose location is inside specified geographical features. Specify if records should be skipped (s) or kept (k) using 1 of 2 formats: **-N**\ *wet/dry*. **-N**\ *ocean/land/lake/island/pond*. [Default is s/k/s/k/s (i.e., s/k), which passes all points on dry land]. .. |Add_-R| replace:: If no map projection is supplied we implicitly set **-Jx**\ 1. |Add_-R_links| .. include:: explain_-R.rst_ :start-after: **Syntax** :end-before: **Description** .. |Add_-V| replace:: |Add_-V_links| .. include:: explain_-V.rst_ :start-after: **Syntax** :end-before: **Description** .. _-Z: **-Z**\ *min*\ [/*max*]\ [**+a**]\ [**+c**\ *col*]\ [**+h**\ [**k**\|\ **s**]]\ [**+i**] Control passing or skipping records (or entire segments) given the selections set via the arguments. Pass all records whose 3rd column (*z*; *col* = 2) lies within the given range or is NaN (use **-s** to skip NaN records). If *max* is omitted then we test if *z* equals *min* instead. This means equality within 5 ULPs (unit of least precision; http://en.wikipedia.org/wiki/Unit_in_the_last_place). To indicate no limit on *min* or *max*, specify a hyphen (-). **Notes**: (1) If your 3rd column is absolute time then remember to supply **-f**\ 2T. (2) To specify several tests just repeat the **Z** option as many times as you have columns to test. (3) To use **-Z**, the input file must have at least three columns. (4) When more than one **Z** option is given then the **-Iz** option cannot be used. Several modifiers are available: - **+a** - In the case of multiple tests, output any record that passes at least one of your *z* tests [Default is all tests must pass]. - **+c** - To specify another *z*-column, append **+c**\ *col*. If **+c** is not used then it is automatically incremented for each new |-Z| option, starting from 2. - **+h** - Instead of obtaining *z* from the data column(s), extract *z* from the segment header |-Z|\ *z* string. If no such entry is found we skip [Default, or **+hs**] the entire segment (or we keep the entire segment if **+hk** was given), otherwise it is subject to the test(s) using the constant *z* for each segment. - **+i** - Reverses the tests to pass record with a *z* value **not** in the given range. .. include:: explain_-aspatial.rst_ .. |Add_-bi| replace:: [Default is 2 input columns]. .. include:: explain_-bi.rst_ .. |Add_-bo| replace:: [Default is same as input]. .. include:: explain_-bo.rst_ .. |Add_-d| unicode:: 0x20 .. just an invisible code .. include:: explain_-d.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_-ocols.rst_ .. include:: explain_-q.rst_ .. include:: explain_-s.rst_ .. include:: explain_-w.rst_ .. include:: explain_colon.rst_ .. include:: explain_help.rst_ .. include:: explain_distunits.rst_ .. include:: explain_precision.rst_ This note applies to ASCII output only in combination with binary or netCDF input or the **-:** option. See also the note below. Note On Processing ASCII Input Records -------------------------------------- Unless you are using the **-:** option, selected ASCII input records are copied verbatim to output. That means that options like **-foT** and settings like :term:`FORMAT_FLOAT_OUT` and :term:`FORMAT_GEO_OUT` will not have any effect on the output. On the other hand, it allows selecting records with diverse content, including character strings, quoted or not, comments, and other non-numerical content. Note On Distances ----------------- If options |-C| or |-L| are selected then distances are Cartesian and in user units; use **-fg** to imply spherical distances in km and geographical (*lon, lat*) coordinates. Alternatively, specify |-R| and **-J** to measure projected Cartesian distances in map units (cm, inch, or points, as determined by :term:`PROJ_LENGTH_UNIT`). This program has evolved over the years. Originally, the |-R| and **-J** were mandatory in order to handle geographic data, but now there is full support for spherical calculations. Thus, |-J| should only be used if you want the tests to be applied on projected data and not the original coordinates. If |-J| is used the distances given via |-C| and |-L| are projected distances. Note On Segments ---------------- Segment headers in the input files are copied to output if one or more records from a segment passes the test. Selection is always done point by point, not by segment. That means only points from a segment that pass the test will be included in the output. If you wish to clip the lines and include the new boundary points at the segment ends you must use :doc:`gmtspatial` instead. Examples -------- .. include:: explain_example.rst_ To only return the data points from the remote file @ship_15.txt that lie within the region between longitudes 246 and 247 and latitudes 20 and 21, try:: gmt select @ship_15.txt -R246/247/20/21 To return all the points *except* those inside that square, use:: gmt select @ship_15.txt -R246/247/20/21 -Ir To extract the subset of data set that is within 300 km of any of the points in pts.txt but more than 100 km away from the lines in lines.txt, run :: gmt select lonlatfile -fg -Cpts.txt+d300k -Llines.txt+d100k -Il > subset.txt Here, you must specify **-fg** so the program knows you are processing geographical data. To keep all points in data.txt within the specified region, except the points on land (as determined by the high-resolution coastlines), use :: gmt select data.txt -R120/121/22/24 -Dh -Nk/s > subset.txt To return all points in quakes.txt that are inside or on the spherical polygon lonlatpath.txt, try :: gmt select quakes.txt -Flonlatpath.txt -fg > subset1.txt To return all points in stations.txt that are within 5 cm of the point in origin.txt for a certain projection, try :: gmt select stations.txt -Corigin.txt+d5 -R20/50/-10/20 -JM20c --PROJ_LENGTH_UNIT=cm > subset2.txt To return all points in quakes.txt that are inside the grid topo.nc where the values are nonzero, try :: gmt select quakes.txt -Gtopo.nc > subset2.txt The pass all records whose 3rd column values fall in the range 10-50 and 5th column values are all negative, try :: gmt select dataset.txt -Z10/50 -Z-/0+c4 > subset3.txt .. include:: explain_gshhg.rst_ .. include:: explain_inside.rst_ See Also -------- :doc:`gmt`, :doc:`gmt.conf`, :doc:`gmtconvert`, :doc:`gmtsimplify`, :doc:`gmtspatial`, :doc:`grdlandmask`, :doc:`coast`