PostGIS  3.1.6dev-r@@SVN_REVISION@@

◆ ptarray_substring()

POINTARRAY* ptarray_substring ( POINTARRAY pa,
double  d1,
double  d2,
double  tolerance 
)

@d1 start location (distance from start / total distance) @d2 end location (distance from start / total distance)

Parameters
tolerancesnap to vertices at locations < tolerance away from given ones

Definition at line 1066 of file ptarray.c.

1067 {
1068  POINTARRAY *dpa;
1069  POINT4D pt;
1070  POINT4D p1, p2;
1071  POINT4D *p1ptr=&p1; /* don't break strict-aliasing rule */
1072  POINT4D *p2ptr=&p2;
1073  int nsegs, i;
1074  double length, slength, tlength;
1075  int state = 0; /* 0=before, 1=inside */
1076 
1077  /*
1078  * Create a dynamic pointarray with an initial capacity
1079  * equal to full copy of input points
1080  */
1081  dpa = ptarray_construct_empty(FLAGS_GET_Z(ipa->flags), FLAGS_GET_M(ipa->flags), ipa->npoints);
1082 
1083  /* Compute total line length */
1084  length = ptarray_length_2d(ipa);
1085 
1086 
1087  LWDEBUGF(3, "Total length: %g", length);
1088 
1089 
1090  /* Get 'from' and 'to' lengths */
1091  from = length*from;
1092  to = length*to;
1093 
1094 
1095  LWDEBUGF(3, "From/To: %g/%g", from, to);
1096 
1097 
1098  tlength = 0;
1099  getPoint4d_p(ipa, 0, &p1);
1100  nsegs = ipa->npoints - 1;
1101  for ( i = 0; i < nsegs; i++ )
1102  {
1103  double dseg;
1104 
1105  getPoint4d_p(ipa, i+1, &p2);
1106 
1107 
1108  LWDEBUGF(3 ,"Segment %d: (%g,%g,%g,%g)-(%g,%g,%g,%g)",
1109  i, p1.x, p1.y, p1.z, p1.m, p2.x, p2.y, p2.z, p2.m);
1110 
1111 
1112  /* Find the length of this segment */
1113  slength = distance2d_pt_pt((POINT2D *)p1ptr, (POINT2D *)p2ptr);
1114 
1115  /*
1116  * We are before requested start.
1117  */
1118  if ( state == 0 ) /* before */
1119  {
1120 
1121  LWDEBUG(3, " Before start");
1122 
1123  if ( fabs ( from - ( tlength + slength ) ) <= tolerance )
1124  {
1125 
1126  LWDEBUG(3, " Second point is our start");
1127 
1128  /*
1129  * Second point is our start
1130  */
1131  ptarray_append_point(dpa, &p2, LW_FALSE);
1132  state=1; /* we're inside now */
1133  goto END;
1134  }
1135 
1136  else if ( fabs(from - tlength) <= tolerance )
1137  {
1138 
1139  LWDEBUG(3, " First point is our start");
1140 
1141  /*
1142  * First point is our start
1143  */
1144  ptarray_append_point(dpa, &p1, LW_FALSE);
1145 
1146  /*
1147  * We're inside now, but will check
1148  * 'to' point as well
1149  */
1150  state=1;
1151  }
1152 
1153  /*
1154  * Didn't reach the 'from' point,
1155  * nothing to do
1156  */
1157  else if ( from > tlength + slength ) goto END;
1158 
1159  else /* tlength < from < tlength+slength */
1160  {
1161 
1162  LWDEBUG(3, " Seg contains first point");
1163 
1164  /*
1165  * Our start is between first and
1166  * second point
1167  */
1168  dseg = (from - tlength) / slength;
1169 
1170  interpolate_point4d(&p1, &p2, &pt, dseg);
1171 
1172  ptarray_append_point(dpa, &pt, LW_FALSE);
1173 
1174  /*
1175  * We're inside now, but will check
1176  * 'to' point as well
1177  */
1178  state=1;
1179  }
1180  }
1181 
1182  if ( state == 1 ) /* inside */
1183  {
1184 
1185  LWDEBUG(3, " Inside");
1186 
1187  /*
1188  * 'to' point is our second point.
1189  */
1190  if ( fabs(to - ( tlength + slength ) ) <= tolerance )
1191  {
1192 
1193  LWDEBUG(3, " Second point is our end");
1194 
1195  ptarray_append_point(dpa, &p2, LW_FALSE);
1196  break; /* substring complete */
1197  }
1198 
1199  /*
1200  * 'to' point is our first point.
1201  * (should only happen if 'to' is 0)
1202  */
1203  else if ( fabs(to - tlength) <= tolerance )
1204  {
1205 
1206  LWDEBUG(3, " First point is our end");
1207 
1208  ptarray_append_point(dpa, &p1, LW_FALSE);
1209 
1210  break; /* substring complete */
1211  }
1212 
1213  /*
1214  * Didn't reach the 'end' point,
1215  * just copy second point
1216  */
1217  else if ( to > tlength + slength )
1218  {
1219  ptarray_append_point(dpa, &p2, LW_FALSE);
1220  goto END;
1221  }
1222 
1223  /*
1224  * 'to' point falls on this segment
1225  * Interpolate and break.
1226  */
1227  else if ( to < tlength + slength )
1228  {
1229 
1230  LWDEBUG(3, " Seg contains our end");
1231 
1232  dseg = (to - tlength) / slength;
1233  interpolate_point4d(&p1, &p2, &pt, dseg);
1234 
1235  ptarray_append_point(dpa, &pt, LW_FALSE);
1236 
1237  break;
1238  }
1239 
1240  else
1241  {
1242  LWDEBUG(3, "Unhandled case");
1243  }
1244  }
1245 
1246 
1247 END:
1248 
1249  tlength += slength;
1250  memcpy(&p1, &p2, sizeof(POINT4D));
1251  }
1252 
1253  LWDEBUGF(3, "Out of loop, ptarray has %d points", dpa->npoints);
1254 
1255  return dpa;
1256 }
#define LW_FALSE
Definition: liblwgeom.h:108
double distance2d_pt_pt(const POINT2D *p1, const POINT2D *p2)
Definition: measures.c:2397
void interpolate_point4d(const POINT4D *A, const POINT4D *B, POINT4D *I, double F)
Find interpolation point I between point A and point B so that the len(AI) == len(AB)*F and I falls o...
Definition: lwgeom_api.c:650
#define FLAGS_GET_Z(flags)
Definition: liblwgeom.h:179
#define FLAGS_GET_M(flags)
Definition: liblwgeom.h:180
int getPoint4d_p(const POINTARRAY *pa, uint32_t n, POINT4D *point)
Definition: lwgeom_api.c:126
#define LWDEBUG(level, msg)
Definition: lwgeom_log.h:83
#define LWDEBUGF(level, msg,...)
Definition: lwgeom_log.h:88
double ptarray_length_2d(const POINTARRAY *pts)
Find the 2d length of the given POINTARRAY (even if it's 3d)
Definition: ptarray.c:1757
POINTARRAY * ptarray_construct_empty(char hasz, char hasm, uint32_t maxpoints)
Create a new POINTARRAY with no points.
Definition: ptarray.c:59
int ptarray_append_point(POINTARRAY *pa, const POINT4D *pt, int repeated_points)
Append a point to the end of an existing POINTARRAY If allow_duplicate is LW_FALSE,...
Definition: ptarray.c:147
double m
Definition: liblwgeom.h:428
double x
Definition: liblwgeom.h:428
double z
Definition: liblwgeom.h:428
double y
Definition: liblwgeom.h:428
uint32_t npoints
Definition: liblwgeom.h:441

References distance2d_pt_pt(), POINTARRAY::flags, FLAGS_GET_M, FLAGS_GET_Z, getPoint4d_p(), interpolate_point4d(), LW_FALSE, LWDEBUG, LWDEBUGF, POINT4D::m, POINTARRAY::npoints, ptarray_append_point(), ptarray_construct_empty(), ptarray_length_2d(), POINT4D::x, POINT4D::y, and POINT4D::z.

Referenced by LWGEOM_line_substring().

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