g.proj: Add JSON support

general/CMakeLists.txt

@@ -26,6 +26,7 @@ build_program_in_subdir(
   DEPENDS
   grass_gis
   grass_gproj
+  grass_parson
   PROJ::proj
   OPTIONAL_DEPENDS
   GDAL::GDAL)

general/g.proj/Makefile

@@ -3,7 +3,7 @@ MODULE_TOPDIR = ../..
 PGM = g.proj
 
 EXTRA_INC = $(PROJINC) $(GDALCFLAGS)
-LIBES = $(GPROJLIB) $(GISLIB) $(GDALLIBS) $(PROJLIB)
+LIBES = $(GPROJLIB) $(GISLIB) $(GDALLIBS) $(PROJLIB) $(PARSONLIB)
 DEPENDENCIES = $(GPROJDEP) $(GISDEP)
 
 include $(MODULE_TOPDIR)/include/Make/Module.make

general/g.proj/g.proj.md

@@ -116,6 +116,24 @@ Print the CRS information for the current project:
 g.proj -p
 ```
 
+Print the CRS information for the current project in JSON format:
+
+```sh
+g.proj -p format=json
+```
+
+Print the CRS information for the current project in WKT JSON format:
+
+```sh
+g.proj -w format=json
+```
+
+Print the CRS information for the current project in PROJ.4 JSON format:
+
+```sh
+g.proj -j format=json
+```
+
 List the possible datum transformation parameters for the current
 project:  
 
@@ -216,6 +234,40 @@ Reproject external vector map to current GRASS project using the OGR
 ogr2ogr -t_srs "`g.proj -wf`" polbnda_italy_GB_ovest.shp polbnda_italy_LL.shp
 ```
 
+### Using g.proj JSON output with pandas
+
+Using the CRS information for the current project in JSON format with pandas:
+
+```python
+  import grass.script as gs
+  import pandas as pd
+
+  # Run g.proj to get CRS information in JSON format.
+  proj_data = gs.parse_command("g.proj", flags="p", format="json")
+
+  df = pd.DataFrame(proj_data, index=[0]).T
+  print(df)
+```
+
+```sh
+                               0
+name     Lambert Conformal Conic
+proj                         lcc
+datum                      nad83
+a                      6378137.0
+es          0.006694380022900787
+lat_1          36.16666666666666
+lat_2          34.33333333333334
+lat_0                      33.75
+lon_0                        -79
+x_0                    609601.22
+y_0                            0
+no_defs                  defined
+unit                       Meter
+units                     Meters
+meters                         1
+```
+
 ## REFERENCES
 
 [PROJ](https://proj.org): Projection/datum support library  

general/g.proj/local_proto.h

@@ -4,6 +4,8 @@ extern struct Key_Value *projinfo, *projunits, *projepsg;
 extern char *projsrid, *projwkt;
 extern struct Cell_head cellhd;
 
+enum OutputFormat { PLAIN, JSON, SHELL };
+
 /* input.c */
 void input_currloc(void);
 
@@ -16,12 +18,12 @@ int input_georef(char *);
 #endif
 
 /* output.c */
-void print_projinfo(int);
+void print_projinfo(enum OutputFormat);
 void print_datuminfo(void);
-void print_proj4(int);
+void print_proj4(int, enum OutputFormat);
 
 #ifdef HAVE_OGR
-void print_wkt(int, int);
+void print_wkt(int, int, enum OutputFormat);
 #endif
 
 /* datumtrans.c */

general/g.proj/main.c

@@ -53,10 +53,12 @@ int main(int argc, char *argv[])
 #endif
         *listcodes, /* list codes of given authority */
         *datum,     /* datum to add (or replace existing datum) */
-        *dtrans;    /* index to datum transform option          */
+        *dtrans,    /* index to datum transform option          */
+        *format;    /* output format */
     struct GModule *module;
 
     int formats;
+    enum OutputFormat outputFormat;
     const char *epsg = NULL;
 
     /* We don't call G_gisinit() here because it validates the
@@ -223,11 +225,31 @@ int main(int argc, char *argv[])
     location->guisection = _("Create");
     location->description = _("Name of new project (location) to create");
 
+    format = G_define_standard_option(G_OPT_F_FORMAT);
+    format->guisection = _("Print");
+
     if (G_parser(argc, argv))
         exit(EXIT_FAILURE);
 
     /* Initialisation & Validation */
 
+    if (strcmp(format->answer, "json") == 0) {
+        outputFormat = JSON;
+    }
+    else if (shellinfo->answer) {
+        outputFormat = SHELL;
+    }
+    else {
+        outputFormat = PLAIN;
+    }
+
+    if (outputFormat == JSON &&
+        !(printinfo->answer || printproj4->answer || printwkt->answer)) {
+        G_fatal_error(_("The 'format=json' option can only be used with one of "
+                        "the -%c, -%c, or -%c flags"),
+                      printinfo->key, printproj4->key, printwkt->key);
+    }
+
     /* list codes for given authority */
     if (listcodes->answer) {
         list_codes(listcodes->answer);
@@ -326,14 +348,14 @@ int main(int argc, char *argv[])
 #endif
     }
     if (printinfo->answer || shellinfo->answer)
-        print_projinfo(shellinfo->answer);
+        print_projinfo(outputFormat);
     else if (datuminfo->answer)
         print_datuminfo();
     else if (printproj4->answer)
-        print_proj4(dontprettify->answer);
+        print_proj4(dontprettify->answer, outputFormat);
 #ifdef HAVE_OGR
     else if (printwkt->answer)
-        print_wkt(esristyle->answer, dontprettify->answer);
+        print_wkt(esristyle->answer, dontprettify->answer, outputFormat);
 #endif
     else if (location->answer)
         create_location(location->answer);