## SYNOPSIS

**project**[

*infile*]

**-F**

*flags*

**-C**

*cx/cy*[

**-A**

*azimuth*] [

**-Dd|g**] [

**-E**

*bx/by*] [

**-G**

*dist*] [

**-H**[

*nrec*] ] [

**-L**[

**w**][

*l_min/l_max*] ] [

**-M**[

*flag*] ] [

**-N**] [

**-Q**] [

**-S**] [

**-T**

*px/py*] [

**-V**] [

**-W**

*w_min/w_max*] [

**-:**] [

**-bi**[

**s**][

*n*] ] [

**-bo**[

**s**][

*n*] ]

## DESCRIPTION

**project**reads arbitrary (

*x, y*[,

*z*]) data from standard input [or

*infile*] and writes to standard output any combination of (

*x, y, z, p, q, r, s*), where (

*p, q*) are the coordinates in the projection, (

*r, s*) is the position in the (

*x, y*) coordinate system of the point on the profile (

*q*= 0 path) closest to (

*x, y*), and

*z*is all remaining columns in the input (beyond the required

*x*and

*y*columns). Alternatively,

**project**may be used to generate (

*r, s, p*) triples at equal increments

*dist*along a profile. In this case (

**-G**option), no input is read. Projections are defined in any (but only) one of three ways: (Definition 1) By a Center

**-C**and an Azimuth

**-A**in degrees clockwise from North. (Definition 2) By a Center

**-C**and end point E of the projection path

**-E**. (Definition 3) By a Center

**-C**and a roTation pole position

**-T**. To spherically project data along a great circle path, an oblique coordinate system is created which has its equator along that path, and the zero meridian through the Center. Then the oblique longitude (

*p*) corresponds to the distance from the Center along the great circle, and the oblique latitude (

*q*) corresponds to the distance perpendicular to the great circle path. When moving in the increasing (

*p*) direction, (toward

*B*or in the

*azimuth*direction), the positive (

*q*) direction is to your left. If a Pole has been specified, then the positive (

*q*) direction is toward the pole. To specify an oblique projection, use the

**-T**option to set the Pole. Then the equator of the projection is already determined and the

**-C**option is used to locate the

*p*= 0 meridian. The Center

*cx/cy*will be taken as a point through which the

*p*= 0 meridian passes. If you do not care to choose a particular point, use the South pole (

*ox*= 0,

*oy*= -90). Data can be selectively windowed by using the

**-L**and

**-W**options. If

**-W**is used, the projection Width is set to use only points with

*w_min*< q <

*w_max*. If

**-L**is set, then the Length is set to use only those points with

*l_min*< p <

*l_max*. If the

**-E**option has been used to define the projection, then

**-Lw**may be selected to window the length of the projection to exactly the span from

**O**to

**B**. Flat earth (cartesian) coordinate transformations can also be made. Set

**-N**and remember that

*azimuth*is clockwise from North (the

*y*axis), NOT the usual cartesian theta, which is counterclockwise from the

*x*axis.

*azimuth*= 90 - theta. No assumptions are made regarding the units for

*x, y, r, s, p, q, dist, l_min, l_max, w_min, w_max*. If

**-Q**is selected, map units are assumed and

*x, y, r, s*must be in degrees and

*p, q, dist, l_min, l_max, w_min, w_max*will be in km.

**project**is CASE SENSITIVE. Use UPPER CASE for all one-letter designators which begin optional arguments. Use lower case for the xyzpqrs letters in

**-flags**.

**-C**-
*cx/cy*sets the origin of the projection, in Definition 1 or 2. If Definition 3 is used (**-T**), then*cx/cy*are the coordinates of a point through which the oblique zero meridian (*p*= 0) should pass.

## OPTIONS

*infile*-
name of ASCII (or binary, see
**-bi**) file(s) with 2 or more columns holding (x,y,[z]) data values. If no filenames are given, project will read from standard input. If the**-G**option is selected, no input data are read. **-F**-
Specify your desired output using any combination of
*xyzpqrs*, in any order. Do not space between the letters. Use lower case. The output will be ASCII (or binary) columns of values corresponding to*xyzpqrs*. If both input and output are using ASCII format then the*z*data are treated as textstring(s). If the**-G**option is selected, the output will be*rsp*. **-A**-
*azimuth*defines the azimuth of the projection (Definition 1). **-D**-
Set the location of the Discontinuity in longitude (
*r*coordinate).**-Dd**will place the discontinuity at the Dateline, (-180 <*r*< 180);**-Dg**will place it at Greenwich, (0 <*r*< 360). Default usually falls at dateline due to*atan2*calls. **-E**-
*bx/by*defines the end point of the projection path (Definition 2). **-G**-
*dist*Generate mode. No input is read. Create (*r, s, p*) output points every*dist*units of*p*. See**-Q**option. **-H**-
Input file(s) has Header record(s). Number of header records can be changed by editing
your .gmtdefaults file. If used,
**GMT**default is 1 header record. **-L**-
Length controls. Project only those points whose
*p*coordinate is within*l_min*<*p*<*l_max*. If**-E**has been set, then you may use**-Lw**to stay within the distance from**C**to**E**. **-M**-
Multiple segment file(s). Segments are separated by a special record.
For ASCII files the first character must be
*flag*[Default is '>']. For binary files all fields must be NaN. **-N**- Flat earth. Make a cartesian coordinate transformation in the plane. [Default uses spherical trigonometry.]
**-Q**-
Map type units, i.e., project assumes
*x, y, r, s*are in degrees while*p, q, dist, l_min, l_max, w_min, w_max*are in km. If**-Q**is not set, then all these are assumed in same units. **-S**-
Sort the output into increasing
*p*order. Useful when projecting random data into a sequential profile. **-T**-
*px/py*sets the position of the roTation pole of the projection. (Definition 3). **-V**- Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
**-W**-
Width controls. Project only those points whose
*q*coordinate is within*w_min*<*q*<*w_max*. **-:**- Toggles between (longitude,latitude) and (latitude,longitude) input/output. [Default is (longitude,latitude)]. Applies to geographic coordinates only.
**-bi**-
Selects binary input. Append
**s**for single precision [Default is double]. Append*n*for the number of columns in the binary file(s). [Default is 2 input columns]. **-bo**-
Selects binary output. Append
**s**for single precision [Default is double].

## EXAMPLES

To generate points every 10km along a great circle from 10N,50W to 30N,10W, try:
**project** **-C**-50/10 **-E**-10/30 **-G**10 **-Q** > great_circle_points.xyp

(Note that great_circle_points.xyp could now be used as input for **grdtrack**, etc. ).

To project the shiptrack gravity, magnetics, and bathymetry in c2610.xygmb along a great circle through an origin at 30S, 30W, the great circle having an azimuth of N20W at the origin, keeping only the data from NE of the profile and within +/- 500 km of the origin, try:

**project** c2610.xygmb **-C**-30/-30 **-A**-20 **-W**-10000/0 **-L**-500/500 **-F**pz **-Q** > c2610_projected.pgmb

(Note in this example that **-W**-10000/0 is used to admit any value with a large negative *q* coordinate. This
will take those points which are on our right as we walk along the great circle path, or to the NE in this example.)

To make a cartesian coordinate transformation of mydata.xy so that the new origin is at 5,3 and the new *x* axis (*p*)
makes an angle of 20 degrees with the old *x* axis, try:

**project** mydata.xy **-C**5/3 **-A**70 **-F**pq > mydata.pq

To take data in the file pacific.lonlat and transform it into oblique coordinates using a pole from the hotspot reference
frame and placing the oblique zero meridian (*p* = 0 line) through Tahiti, try:

**project** pacific.lonlat **-T**-75/68 **-C**-149:26/-17:37 **-F**pq > pacific.pq

Suppose that pacific_topo.grd is a grdfile of bathymetry, and you want to make a file of flowlines in the hotspot reference frame. If you try:

**grd2xyz** pacific_topo.grd | **project** **-T**-75/68 **-C**0/-90 **-F**xyq | **xyz2grd**
**-R***etc* **-I***etc* **-C**flow.grd

then flow.grd is a file in the same area as pacific_topo.grd, but flow contains the latitudes about the pole of the projection.
You now can use grdcontour on flow.grd to draw lines of constant oblique latitude, which are flow lines in the hotspot frame.

If you have an arbitrarily rotation pole *px/py* and you would like to draw an oblique small circle on a map, you
will first need to make a file with the oblique coordinates for the small circle (i.e., lon = 0-360, lat is constant), then create
a file with two records: the north pole (0/90) and the origin (0/0), and find what their oblique coordinates are using your
rotation pole. Now, use the projected North pole and origin coordinates as the rotation pole and center, respectively,
and project your file as in the pacific example above. This gives coordinates for an oblique small circle.