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/******************************************************************************
*
* Project: Shapelib
* Purpose: Commandline program to generate points-in-polygons from a
* shapefile as a shapefile.
* Author: Marko Podgorsek, d-mon@siol.net
*
******************************************************************************
* Copyright (c) 2004, Marko Podgorsek, d-mon@siol.net
*
* SPDX-License-Identifier: MIT OR LGPL-2.0-or-later
******************************************************************************
*
*/
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <shapefil.h>
#define MAXINTERSECTIONPOINTS 255
enum loopDir
{
kExterior,
kInterior,
kError
};
struct DPoint2d
{
DPoint2d()
{
x = y = 0.0;
};
DPoint2d(double x, double y)
{
this->x = x;
this->y = y;
};
double x, y;
};
struct IntersectPoint
{
IntersectPoint(void)
{
x = y = 0.0;
boundry_nmb = 0;
loopdirection = kError;
};
double x, y;
int boundry_nmb;
loopDir loopdirection;
};
static loopDir LoopDirection(DPoint2d *vertices, int vertsize)
{
int i;
double sum = 0.0;
for (i = 0; i < vertsize - 1; i++)
{
sum += (vertices[i].x * vertices[i + 1].y) -
(vertices[i].y * vertices[i + 1].x);
}
if (sum > 0)
return kInterior;
else
return kExterior;
}
static DPoint2d CreatePointInPoly(SHPObject *psShape, int quality)
{
int i, j, k, end, vert;
double part, dx, xmin, xmax, ymin, ymax, x3, x4, y3, y4, len, maxlen = 0;
DPoint2d *vertices;
loopDir direction;
IntersectPoint mp1, mp2, point1, point2, points[MAXINTERSECTIONPOINTS];
xmin = psShape->dfXMin;
ymin = psShape->dfYMin;
xmax = psShape->dfXMax;
ymax = psShape->dfYMax;
part = (ymax - ymin) / (quality + 1);
dx = xmax - xmin;
for (i = 0; i < quality; i++)
{
const double y = ymin + part * (i + 1);
int pointpos = 0;
for (j = 0; j < psShape->nParts; j++)
{
if (j == psShape->nParts - 1)
end = psShape->nVertices;
else
end = psShape->panPartStart[j + 1];
vertices = new DPoint2d[end - psShape->panPartStart[j]];
for (k = psShape->panPartStart[j], vert = 0; k < end; k++)
{
vertices[vert].x = psShape->padfX[k];
vertices[vert++].y = psShape->padfY[k];
}
direction = LoopDirection(vertices, vert);
for (k = 0; k < vert - 1; k++)
{
y3 = vertices[k].y;
y4 = vertices[k + 1].y;
if ((y3 >= y && y4 < y) ||
(y3 <= y &&
y4 >
y)) //I check >= only once, because if it's not checked now (y3) it will be in the next iteration (which is y4 now)
{
point1.boundry_nmb = j;
point1.loopdirection = direction;
x3 = vertices[k].x;
x4 = vertices[k + 1].x;
if (y3 == y)
{
point1.y = y3;
point1.x = x3;
if (direction ==
kInterior) //add point 2 times if the direction is interior, so that the final count of points is even
{
points[pointpos++] = point1;
}
}
else
{
point1.x =
xmin +
(((((x4 - x3) * (y - y3)) -
((y4 - y3) * (xmin - x3))) /
((y4 - y3) * dx)) *
dx); //striped down calculation of intersection of 2 lines
point1.y = y;
}
points[pointpos++] = point1;
}
}
delete[] vertices;
}
for (j = 1; j < pointpos;
j++) //sort the found intersection points by x value
{
for (k = j; k > 0; k--)
{
if (points[k].x < points[k - 1].x)
{
point1 = points[k];
points[k] = points[k - 1];
points[k - 1] = point1;
}
else
{
break;
}
}
}
for (j = 0; j < pointpos - 1; j++)
{
point1 = points[j];
point2 = points[j + 1];
if ((point1.loopdirection ==
kExterior && //some checkings for valid point
point2.loopdirection == kExterior &&
point1.boundry_nmb == point2.boundry_nmb && j % 2 == 0) ||
(point1.loopdirection == kExterior &&
point2.loopdirection == kInterior) ||
(point1.loopdirection == kInterior &&
point2.loopdirection == kExterior))
{
len = sqrt(pow(point1.x - point2.x, 2) +
pow(point1.y - point2.y, 2));
if (len >= maxlen)
{
maxlen = len;
mp1 = point1;
mp2 = point2;
}
}
}
}
return DPoint2d((mp1.x + mp2.x) * 0.5, (mp1.y + mp2.y) * 0.5);
}
int main(int argc, char *argv[])
{
if (argc != 3)
{
printf("Usage: %s shpfile_path quality\n", argv[0]);
return 1;
}
int i, nEntities, quality;
SHPHandle hSHP;
DPoint2d pt;
quality = atoi(argv[2]);
hSHP = SHPOpen(argv[1], "rb");
SHPGetInfo(hSHP, &nEntities, NULL, NULL, NULL);
printf("PointInPoly v1.0, by Marko Podgorsek\n----------------\n");
for (i = 0; i < nEntities; i++)
{
SHPObject *psShape = SHPReadObject(hSHP, i);
if (psShape->nSHPType == SHPT_POLYGON)
{
pt = CreatePointInPoly(psShape, quality);
printf("%d: x=%f y=%f\n", i, pt.x, pt.y);
}
SHPDestroyObject(psShape);
}
SHPClose(hSHP);
return 0;
}
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