From d5d60b7154d149de797737ecd96fde56bfecb7c2 Mon Sep 17 00:00:00 2001
From: "Toby C. Wilkinson" <open@tobywilkinson.co.uk>
Date: Mon, 20 Dec 2021 19:22:46 +0000
Subject: Fix and additional options for Peirce Quincuncial projections (#2978)

This fixes the current forward implementation of Peirce Quincuncial proj to correctly flip/reflect out the southern hemisphere to four triangles, and rotate entire result to a square or diamond. (It there resolves the issues identified with pull request https://github.com/OSGeo/PROJ/pull/2230 , where southern hemisphere was wrongly projected over northern, and reverses the restriction to northern hemisphere introduced there). It also adds additional lateral projection of the hemispheres.

- This PR adds an optional parameter `+type` which allows selection of projection. The `+type=square` and `+type=diamond` types match in principle ESRI's twin implementations of square and diamond PQ projs. The **default** if not specified is `+type=diamond`.

- The previous behaviour restricted to the northern hemisphere can be reproduced using the `+type=nhemisphere`, though this is an edge case only.

- An additional `+type=horizontal` and `+type=vertical` rectangular lateral versions have been added that place each hemisphere side-by-side. This is primarily to allow creation of projections such as Greiger Triptychial, which also require the additional optional params `scrollx` or `scrolly` in order to shift parts of the projection from one side of the map to the other.

- Additional documentation has been added to proj description, including quoting the usual meridian used in common usage of projection, and images showing the different types.
---
 docs/plot/plotdefs.json | 39 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 36 insertions(+), 3 deletions(-)

(limited to 'docs/plot/plotdefs.json')

diff --git a/docs/plot/plotdefs.json b/docs/plot/plotdefs.json
index 1e9c05ee..a6d70273 100644
--- a/docs/plot/plotdefs.json
+++ b/docs/plot/plotdefs.json
@@ -1051,13 +1051,46 @@
         "type": "poly"
     },
     {
-        "filename": "peirce_q.png",
+        "filename": "peirce_q_square.png",
         "latmax": 90,
-        "latmin": 0,
+        "latmin": -90,
+        "lonmax": 180,
+        "lonmin": -180,
+        "name": "peirce_q_square",
+        "projstring": "+proj=peirce_q +lon_0=25 +type=square",
+        "res": "low",
+        "type": "poly"
+    },
+    {
+        "filename": "peirce_q_diamond.png",
+        "latmax": 90,
+        "latmin": -90,
         "lonmax": 180,
         "lonmin": -180,
         "name": "peirce_q",
-        "projstring": "+proj=peirce_q",
+        "projstring": "+proj=peirce_q +lon_0=25 +type=diamond",
+        "res": "low",
+        "type": "poly"
+    },
+    {
+        "filename": "peirce_q_horizontal.png",
+        "latmax": 90,
+        "latmin": -90,
+        "lonmax": 180,
+        "lonmin": -180,
+        "name": "peirce_q_horizontal",
+        "projstring": "+proj=peirce_q +lon_0=25 +type=horizontal",
+        "res": "low",
+        "type": "line"
+    },
+    {
+        "filename": "grieger_triptychial.png",
+        "latmax": 90,
+        "latmin": -90,
+        "lonmax": 180,
+        "lonmin": -180,
+        "name": "grieger_triptychial",
+        "projstring": "+proj=pipeline +step +proj=ob_tran +o_proj=peirce_q +o_lat_p=-45 +o_lon_p=45 +type=horizontal +scrollx=-0.25 +step +proj=affine +s11=-1 +s12=0 +s21=0 +s22=-1",
         "res": "low",
         "type": "poly"
     },
-- 
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