Provided by: gmt-common_5.4.5+dfsg-1_all

**NAME**

gmtspatial - Do geospatial operations on lines and polygons

**SYNOPSIS**

gmtspatial[table] [-A[amin_dist][unit]] [-C] [-D[+ffile][+aamax][+ddmax][+c|Ccmax][+sfact] ] [-E+|-] [-F[l] ] [-I[e|i] ] [-Npfile[+a][+pstart][+r][+z] ] [-Q[[-|+]unit][+cmin[/max]][+h][+l][+p][+s[a|d]] ] [-Rregion] [-Si|u|s|j] [-T[clippolygon] ] [-V[level] ] [-bbinary ] [-dnodata ] [-eregexp ] [-fflags ] [-ggaps ] [-hheaders ] [-iflags ] [-oflags ] [-:[i|o] ]Note:No space is allowed between the option flag and the associated arguments.

**DESCRIPTION**

gmtspatialreads one or more data files (which may be multisegment files) that contains closed polygons and operates of these polygons in the specified way. Operations include area calculation, handedness reversals, and polygon intersections.

**REQUIRED** **ARGUMENTS**

None.

**OPTIONAL** **ARGUMENTS**

tableOne or more ASCII (or binary, see-bi[ncols][type]) data table file(s) holding a number of data columns. If no tables are given then we read from standard input.-A[amin_dist][unit] Perform spatial nearest neighbor (NN) analysis: Determine the nearest neighbor of each point and report the NN distances and the point IDs involved in each pair (IDs are the input record numbers starting at 0). Use-Aato decimate a data set so that no NN distance is lower than the thresholdmin_dist. In this case we write out the (possibly averaged) coordinates and the updated NN distances and point IDs. A negative point number means the original point was replaced by a weighted average (the absolute ID value gives the ID of the first original point ID to be included in the average.). Note: The input data are assumed to contain (lon,lat) or (x,y), optionally followed by azand aweight[1] column. We compute a weighted average of the location andz(if present).-CClips polygons to the map region, including map boundary to the polygon as needed. The result is a closed polygon (see-Tfor truncation instead). Requires-R.-D[+ffile][+aamax][+ddmax][+c|Ccmax][+sfact] Check for duplicates among the input lines or polygons, or, iffileis given via+f, check if the input features already exist among the features infile. We consider the cases of exact (same number and coordinates) and approximate matches (average distance between nearest points of two features is less than a threshold). We also consider that some features may have been reversed. Features are considered approximate matches if their minimum distance is less thandmax[0] (see UNITS) and their closeness (defined as the ratio between the average distance between the features divided by their average length) is less thancmax[0.01]. For each duplicate found, the output record begins with the single letter Y (exact match) or ~ (approximate match). If the two matching segments differ in length by more than a factor of 2 then we consider the duplicate to be either a subset (-) or a superset (+). Finally, we also note if two lines are the result of splitting a continuous line across the Dateline (|). For polygons we also consider the fractional difference in areas; duplicates must differ by less thanamax[0.01]. By default, we compute the mean line separation. Use+Ccminto instead compute the median line separation and therefore a robust closeness value. Also by default we consider all distances between points on one line and another. Append+pto limit the comparison to points that project perpendicularly to points on the other line (and not its extension).-E+|-] Reset the handedness of all polygons to match the given+(counter-clockwise) or-(clockwise). Implies-Q+.-F[l] Force input data to become polygons on output, i.e., close them explicitly if not already closed. Optionally, appendlto force line geometry.-I[e|i] Determine the intersection locations between all pairs of polygons. Appendito only compute internal (i.e., self-intersecting polygons) crossovers oreto only compute external (i.e., between paris of polygons) crossovers [Default is both].-Npfile[+a][+pstart][+r][+z] Determine if one (or all, with+a) points of each feature in the input data are inside any of the polygons given in thepfile. If inside, then report which polygon it is; the polygon ID is either taken from the aspatial value assigned to Z, the segment header (first-Z, then-Lare scanned), or it is assigned the running number that is initialized tostart[0]. By default the input segment that are found to be inside a polygon are written to stdout with the polygon ID encoded in the segment header as-ZID. Alternatively, append+rto just report which polygon contains a feature or+zto have the IDs added as an extra data column on output. Segments that fail to be inside a polygon are not written out. If more than one polygon contains the same segment we skip the second (and further) scenario.-Q[[-|+]unit][+cmin[/max]][+h][+l][+p][+s[a|d]] Measure the area of all polygons or length of line segments. Use-Q+hto append the area to each polygons segment header [Default simply writes the area to stdout]. For polygons we also compute the centroid location while for line data we compute the mid-point (half-length) position. Append a distance unit to select the unit used (see UNITS). Note that the area will depend on the current setting of PROJ_ELLIPSOID; this should be a recent ellipsoid to get accurate results. The centroid is computed using the mean of the 3-D Cartesian vectors making up the polygon vertices, while the area is obtained via an equal-area projection. For line lengths you may prepend-|+to the unit and the calculation will use Flat Earth or Geodesic algorithms, respectively [Default is great circle distances]. Normally, all input segments will be be reflected on output. Usecto restrict processing to those whose length (or area for polygons) fall inside the specified range set byminandmax. Ifmaxis not set it defaults to infinity. To sort the segments based on their lengths or area, usesand appendafor ascending anddfor descending order [ascending]. By default, we consider open polygons as lines. Append+pto close open polygons and thus consider all input as polygons, or append+lto consider all input as lines, even if closed.-Rwest/east/south/north[/zmin/zmax][+r][+uunit]west,east,south, andnorthspecify the region of interest, and you may specify them in decimal degrees or in [±]dd:mm[:ss.xxx][W|E|S|N] format Append+rif lower left and upper right map coordinates are given instead of w/e/s/n. The two shorthands-Rgand-Rdstand for global domain (0/360 and -180/+180 in longitude respectively, with -90/+90 in latitude). Alternatively for grid creation, giveRcodelon/lat/nx/ny, wherecodeis a 2-character combination of L, C, R (for left, center, or right) and T, M, B for top, middle, or bottom. e.g., BL for lower left. This indicates which point on a rectangular region thelon/latcoordinate refers to, and the grid dimensionsnxandnywith grid spacings via-Iis used to create the corresponding region. Alternatively, specify the name of an existing grid file and the-Rsettings (and grid spacing, if applicable) are copied from the grid. Appending+uunitexpects projected (Cartesian) coordinates compatible with chosen-Jand we inversely project to determine actual rectangular geographic region. For perspective view (-p), optionally append /zmin/zmax. In case of perspective view (-p), a z-range (zmin,zmax) can be appended to indicate the third dimension. This needs to be done only when using the-Jzoption, not when using only the-poption. In the latter case a perspective view of the plane is plotted, with no third dimension. Clips polygons to the map region, including map boundary to the polygon as needed. The result is a closed polygon.-Si|j|s|uSpatial processing of polygons. Choose from-Siwhich returns the intersection of polygons (closed),-Suwhich returns the union of polygons (closed),-Sswhich will split polygons that straddle the Dateline, and-Sjwhich will join polygons that were split by the Dateline. Note: Only-Sshas been implemented.-T[clippolygon] Truncate polygons against the specified polygon given, possibly resulting in open polygons. If no argument is given to-Twe create a clipping polygon from-Rwhich then is required. Note that when the-Rclipping is in effect we will also look for polygons of length 4 or 5 that exactly match the-Rclipping polygon.-V[level] (more ...) Select verbosity level [c].-bi[ncols][t] (more ...) Select native binary input. [Default is 2 input columns].-bo[ncols][type] (more ...) Select native binary output. [Default is same as input].-d[i|o]nodata(more ...) Replace input columns that equalnodatawith NaN and do the reverse on output.-e[~]"pattern"|-e[~]/regexp/[i] (more ...) Only accept data records that match the given pattern.-f[i|o]colinfo(more ...) Specify data types of input and/or output columns.-g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...) Determine data gaps and line breaks.-h[i|o][n][+c][+d][+rremark][+rtitle] (more ...) Skip or produce header record(s).-icols[+l][+sscale][+ooffset][,...] (more ...) Select input columns and transformations (0 is first column).-ocols[,...] (more ...) Select output columns (0 is first column).-:[i|o] (more ...) Swap 1st and 2nd column on input and/or output.-^or just-Print a short message about the syntax of the command, then exits (NOTE: on Windows just use-).-+or just+Print an extensive usage (help) message, including the explanation of any module-specific option (but not the GMT common options), then exits.-?or no arguments Print a complete usage (help) message, including the explanation of all options, then exits.

**UNITS**

For map distance unit, appendunitdfor arc degree,mfor arc minute, andsfor arc second, orefor meter [Default],ffor foot,kfor km,Mfor statute mile,nfor nautical mile, andufor US survey foot. By default we compute such distances using a spherical approximation with great circles. Prepend-to a distance (or the unit is no distance is given) to perform "Flat Earth" calculations (quicker but less accurate) or prepend+to perform exact geodesic calculations (slower but more accurate).

**ASCII** **FORMAT** **PRECISION**

The ASCII output formats of numerical data are controlled by parameters in your gmt.conf file. Longitude and latitude are formatted according to FORMAT_GEO_OUT, absolute time is under the control of FORMAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point values are formatted according to FORMAT_FLOAT_OUT. Be aware that the format in effect can lead to loss of precision in ASCII output, which can lead to various problems downstream. If you find the output is not written with enough precision, consider switching to binary output (-boif available) or specify more decimals using the FORMAT_FLOAT_OUT setting.

**EXAMPLE**

To turn all lines in the multisegment file lines.txt into closed polygons, run gmt spatial lines.txt -F > polygons.txt To compute the area of all geographic polygons in the multisegment file polygons.txt, run gmt spatial polygons.txt -Q > areas.txt Same data, but now orient all polygons to go counter-clockwise and write their areas to the segment headers, run gmt spatial polygons.txt -Q+h -E+ > areas.txt To determine the areas of all the polygon segments in the file janmayen_land_full.txt, add this information to the segment headers, sort the segments from largest to smallest in area but only keep polygons with area larger than 1000 sq. meters, run gmt spatial -Qe+h+p+c1000+sd -V janmayen_land_full.txt > largest_pols.txt To determine the intersections between the polygons A.txt and B.txt, run gmt spatial A.txt B.txt -Ie > crossovers.txt To truncate polygons A.txt against polygon B.txt, resulting in an open line segment, run gmt gmtspatial A.txt -TB.txt > line.txt

**NOTES**

OGR/GMT files are considered complete datasets and thus you cannot specify more than one at a given time. This causes problems if you want to examine the intersections of two OGR/GMT files. The solution is to convert them to regular datasets via gmtconvert and then rungmtspatialon the converted files.

**SEE** **ALSO**

gmt, gmtconvert, gmtselect, gmtsimplify

**COPYRIGHT**

2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe