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Overview
Comment:Add the geopoly_read() SQL function to the geopoly.c extension.
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SHA3-256: b37625e8e469f8856b19acabe9a6628322cba2e76d478da18caff4d9613ab5e6
User & Date: drh 2018-05-11 15:38:03
Context
2018-05-11
16:50
Add the geopoly_within() SQL function. check-in: 927d52a9 user: drh tags: geojson
15:38
Add the geopoly_read() SQL function to the geopoly.c extension. check-in: b37625e8 user: drh tags: geojson
14:02
Fix a typo in the help message from the ".sha3sum" command in the CLI. check-in: e76f676c user: drh tags: geojson
Changes
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Changes to ext/misc/geopoly.c.

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}


/*
** Implementation of the geopoly_area(X) function.
**
** If the input is a well-formed Geopoly BLOB then return the area


** enclosed by the polygon.  Otherwise return NULL.
*/
static void geopolyAreaFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){















}


#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_geopoly_init(







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}


/*
** Implementation of the geopoly_area(X) function.
**
** If the input is a well-formed Geopoly BLOB then return the area
** enclosed by the polygon.  If the polygon circulates clockwise instead
** of counterclockwise (as it should) then return the negative of the
** enclosed area.  Otherwise return NULL.
*/
static void geopolyAreaFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0]);
  if( p ){
    double rArea = 0.0;
    int ii;
    for(ii=0; ii<p->nVertex-1; ii++){
      rArea += (p->a[ii*2] - p->a[ii*2+2])           /* (x0 - x1) */
                * (p->a[ii*2+1] + p->a[ii*2+3])      /* (y0 + y1) */
                * 0.5;
    }
    rArea += (p->a[ii*2] - p->a[0])                  /* (xN - x0) */
             * (p->a[ii*2+1] + p->a[1])              /* (yN + y0) */
             * 0.5;
    sqlite3_result_double(context, rArea);
    sqlite3_free(p);
  }            
}


#ifdef _WIN32
__declspec(dllexport)
#endif
int sqlite3_geopoly_init(