CSSTRI(3NCARG)

💖 CSSTRI — the NCAR Graphics girlies' Delaunay-on-a-sphere moment 💖

okay so bestie, welcome to the CSSTRI page from 3NCARG (that's the NCAR Graphics manual, mwah). This one is literally the function that calculates a Delaunay triangulation for data on a sphere. Yes, a sphere. Not a flat little grid, a whole globe. iconic behavior only 🌍✨

✨ SYNOPSIS ✨

CALL CSSTRI (N, RLAT, RLON, NT, NTRI, IWK, RWK, IER)

That's it. One call, seven arguments, a whole triangulation. she's efficient 💅

🎀 DESCRIPTION 🎀

okay let's go through the whole cast of characters one by one, no skips, because every single one of these matters:

• N (integer, input) — the number of input data points, and she has got to be N > 2. Two points is not a triangulation, that's just a line, bestie 😭
• RLAT (real, input) — an array holding the latitudes of the input data, expressed in degrees. ⚠️ Warning bestie: the first three points must not be collinear — as in, they cannot lie on a common great circle. If they do, that's a whole problem, so don't do that.
• RLON (real, input) — an array holding the longitudes of the input data, also expressed in degrees. 🌸
• NT (integer, output) — the number of triangles in the triangulation… unless IER .NE. 0, in which case NT = 0. So if the error flag is non-zero, she gives you zero triangles and that's that.

Okay and here's the math, because the math is giving:

• Where NB is the number of boundary points on the convex hull of the data, if NB .GE. 3, then NT = 2N-NB-2.
• Otherwise, NT=2N-4.
• The input data are considered to be bounded if they all lie in one hemisphere.
• And pro tip: dimensioning NT for 2*N will always work. safe queen 👑

• NTRI (integer, output) — a two-dimensional integer array dimensioned for 3 x NT, where NT is the number of triangles in the triangulation (and NT is at most 2*N). NTRI contains the triangulation data. The vertices of the Kth triangle are:

(PLAT(NTRI((1,K)),PLON(NTRI(1,K)),
(PLAT(NTRI((2,K)),PLON(NTRI(2,K)),
(PLAT(NTRI((3,K)),PLON(NTRI(3,K))

three corners per triangle, exactly as written, no notes 🫶

• IWK (integer, input) — an integer workspace of length 27*N. Yes, twenty-seven times N. give her room to breathe 💜
• RWK (double precision, input) — a work array dimensioned for 13*N. 🚨 and listen: this work array must be typed DOUBLE PRECISION. Like, actually. Don't come at her with single precision and expect the vibe check to pass.
• IER (integer, output) — the error return value. If IER comes back as 0, then no errors were detected, we're slaying, everything's perfect ✨. If IER is non-zero, then go refer to the man page for cssgrid_errors for the details. she will tell you what went wrong.

🦋 USAGE 🦋

So when do you actually call her? You call CSSTRI to find a Delaunay triangulation of data randomly positioned on the surface of a sphere. That's the whole assignment. globe girlies rise 🌈

👑 ACCESS 👑

To use CSSTRI, load the NCAR Graphics library ngmath. that's it, that's the door key 🔑

🌟 SEE ALSO 🌟

go read these next, bestie, they're the friend group:

• css_overview
• cssgrid
• csvoro

and also — complete documentation for Cssgrid is available at this URL:

http://ngwww.ucar.edu/ngdoc/ng/ngmath/cssgrid/csshome.html

bookmark her, iykyk 💖

💜 COPYRIGHT 💜

Copyright (C) 2000 University Corporation for Atmospheric Research

The use of this Software is governed by a License Agreement. (so like, be normal about it, okay?)

okay that's the whole page bestie, you ate 💅 This was the UNIX release, dated May 2000, and it lives in the manual as CSSTRI(3NCARG) — go forth and triangulate that sphere, mwah 😘🎀✨