Convert grdblend test to documentation figure (#7968)

* Convert grdblend test to documentation figure

Removing the old test/grdblend/blend.sh and add doc/scripts/GMT_blend.sh instead, with figure link in grdblend documentation.

* Rename script

* Create GMT_blend.sh

* Update images.dvc

* Update grdblend.rst

doc/rst/source/grdblend.rst

@@ -117,6 +117,16 @@ Optional Arguments
     for subsequent grids we only consider them in the decision if the
     values are :math:`z \ge 0` (**+p**) or :math:`z \le 0` (**+n**), respectively.
 
+
+.. figure:: /_images/GMT_blendtype.*
+   :width: 500 px
+   :align: center
+
+   Blending is just one option what happens in areas of overlap. The dashed
+   lines indicates the "inner" regions where the relative weights are 1 and
+   between the dashed lines and the grid borders the relative weights are
+   cosine-tapered down to 0.
+
 .. _-Q:
 
 **-Q**

doc/scripts/GMT_blendtype.sh

@@ -0,0 +1,97 @@
+#!/usr/bin/env bash
+#
+
+# "Inner" regions when blending (dashed lines)
+cat << EOF > info.txt
+a.nc	-R1/5/1/5	1
+b.nc	-R5/10/1/4	1
+c.nc	-R5/9/5/9	1
+d.nc	-R1/5/5/9	1
+EOF
+# Make 4 constant grids
+gmt grdmath -R0/6/0/6 -I0.1   0 = a.nc
+gmt grdmath -R4/10/0/5 -I0.1  2 = b.nc
+gmt grdmath -R0/6/4/10 -I0.1  8 = c.nc
+gmt grdmath -R4/10/4/10 -I0.1 4 = d.nc
+
+gmt begin GMT_blendtype
+	gmt set GMT_THEME cookbook FONT_TAG 10p,Helvetica-Bold,black FONT_ANNOT_PRIMARY 8p
+	gmt makecpt -Crainbow -T0/8
+	gmt subplot begin 2x3 -Fs5c/3c -Sct -Srl -R0/10/0/10 -A0+jTR
+	gmt subplot set 0 -Aaverage
+	# 0. Just add them up
+	gmt grdblend ?.nc -R0/10/0/10 -I0.1 -Gblend.nc
+	gmt grdimage blend.nc
+	# Draw grid outlines
+	cat <<- EOF > lines.txt
+	> a
+	6	0
+	6	6
+	0	6
+	> b
+	4	0
+	4	5
+	10	5
+	> c
+	4	10
+	4	4
+	10	4
+	> d
+	6	10
+	6	4
+	0	4
+	EOF
+	gmt plot lines.txt -W1p
+	# 1. Blend the overlapping grids
+	gmt grdblend info.txt -I0.1 -Gblend.nc
+	gmt subplot set 1 -Ablend
+	gmt grdimage blend.nc
+	gmt plot lines.txt -W1p
+	# Draw the inside regions
+	gmt plot -W0.5p,- -L <<- EOF
+	> a
+	1	1
+	5	1
+	5	5
+	1	5
+	> b
+	5	1
+	10	1
+	10	4
+	5	4
+	> c
+	5	5
+	9	5
+	9	9
+	5	9
+	> d
+	1	5
+	5	5
+	5	9
+	1	9
+	EOF
+	# 2. Last grid encountered matters
+	gmt grdblend ?.nc -Co -I0.1 -Gblend.nc
+	gmt subplot set 2 -Alast
+	gmt grdimage blend.nc 
+	gmt plot lines.txt -W1p
+	# 3. First grid encountered matters
+	gmt grdblend ?.nc -Cf -I0.1 -Gblend.nc
+	gmt subplot set 3 -Afirst
+	gmt grdimage blend.nc
+	gmt plot  lines.txt -W1p
+	# 4. Grid with lowest value matters
+	gmt grdblend ?.nc -Cl -I0.1 -Gblend.nc
+	gmt subplot set 4 -Alow
+	gmt grdimage blend.nc
+	gmt plot lines.txt -W1p
+	# 5. Grid with highest value matters
+	gmt grdblend ?.nc -Cu -I0.1 -Gblend.nc
+	gmt subplot set 5 -Ahigh
+	gmt grdimage blend.nc
+	gmt plot lines.txt -W1p
+	gmt subplot end
+	gmt colorbar -DJRM -B1
+gmt end show
+
+

doc/scripts/images.dvc

@@ -1,5 +1,5 @@
 outs:
-- md5: c80408f923113a2ef18ad98111b0496a.dir
-  size: 33225142
-  nfiles: 201
+- md5: d32873164f988cee578babc564af6bd6.dir
+  size: 33333883
+  nfiles: 203
   path: images

test/baseline/grdblend.dvc

@@ -1,5 +1,5 @@
 outs:
-- md5: 45920baa4aca533105ba984d12245bb5.dir
-  size: 319127
-  nfiles: 8
+- md5: c26aa6d39feeec2780603ba7ebe3eaf9.dir
+  size: 266208
+  nfiles: 7
   path: grdblend

test/baseline/psxy.dvc

@@ -1,5 +1,5 @@
 outs:
-- md5: 5c6184bff710b71e7134155b26ca285f.dir
-  size: 9377472
-  nfiles: 143
+- md5: 239f4bd18d38b222c7da4a1fa70bb7aa.dir
+  size: 9322544
+  nfiles: 142
   path: psxy