Construct Points on polyline at 3d distance
It would be nice if there there were additional methods for 3D measurements. All methods are 2D on the polyline geometry. There is the segmentAlongLine method that mentions measures, so I was hopeful that converting the geometry to Polyline ZM would allow for extracting a sub-segment and use the lastPoint of the polyline to get the point. In a previous thread I published a snippet to convert a PolylineZ to PolylineZM and assign the 3D length as M value:
https://community.esri.com/message/516789#comment-516789
That turned out to be wrong. So I used the snippet and shaped it a little bit to create a positionAlongLine3D function.
def main(): import arcpy arcpy.env.overwriteOutput = True sr = arcpy.SpatialReference(28992) lst_coords = [[[0, 0, 0], [1000, 0, 0], [1000, 1000, 0], [0, 1000, 0], [0, 0, 0]], [[2000, 0, 0], [3000, 0, 1000], [3000, 1000, 2000], [2000, 1000, 3000], [2000, 0, 4000]]] lines = [] points = [] lines_m = [] points_m = [] points_ok = [] for feature in lst_coords: polyline = arcpy.Polyline( arcpy.Array([arcpy.Point(*coords) for coords in feature]), sr, True, False) lines.append(polyline) segment = polyline.segmentAlongLine(0, 2500, False) points.append(arcpy.PointGeometry(segment.lastPoint, sr, True, False)) polyline_zm = CreateZAwareFeature(polyline, sr) lines_m.append(polyline_zm) segment_m = polyline_zm.segmentAlongLine(0, 2500, False) points_m.append(arcpy.PointGeometry(segment_m.lastPoint, sr, True, True)) pnt_ok = positionAlongLine3D(polyline, 2500) points_ok.append(pnt_ok) arcpy.CopyFeatures_management(lines, r'C:\GeoNet\Query3DpointAndDistance\test.gdb\lines') arcpy.CopyFeatures_management(points, r'C:\GeoNet\Query3DpointAndDistance\test.gdb\points') arcpy.CopyFeatures_management(lines_m, r'C:\GeoNet\Query3DpointAndDistance\test.gdb\lines_m') arcpy.CopyFeatures_management(points_m, r'C:\GeoNet\Query3DpointAndDistance\test.gdb\points_m') arcpy.CopyFeatures_management(points_ok, r'C:\GeoNet\Query3DpointAndDistance\test.gdb\points_ok') def positionAlongLine3D(polyline_z, dist): length = 0 if dist <= 0: return arcpy.PointGeometry(polyline_z.firstPoint, polyline_z.spatialReference, True) elif dist >= polyline_z.length: return arcpy.PointGeometry(polyline_z.lastPoint, polyline_z.spatialReference, True) else: for part in polyline_z: cnt = 0 for pnt in part: if cnt == 0: pnt_prev = arcpy.Point(pnt.X, pnt.Y, pnt.Z) length += get3DLength(pnt, pnt_prev) if length > dist: d1 = dist - prev_length seg_length = length - prev_length frac = d1 / seg_length segment = arcpy.Polyline(arcpy.Array([pnt_prev, pnt]), polyline_z.spatialReference) pnt_3d = segment.positionAlongLine(frac, True) z = (1-frac) * pnt_prev.Z + frac * pnt.Z pntz = arcpy.Point(pnt_3d.firstPoint.X, pnt_3d.firstPoint.Y, z) return arcpy.PointGeometry(pntz, polyline_z.spatialReference, True) break cnt += 1 pnt_prev = pnt prev_length = length def CreateZAwareFeature(polyline_z, sr): lst_poly_zm = [] length = 0 for part in polyline_z: part_zm = [] cnt = 0 for pnt in part: if cnt == 0: pnt_prev = arcpy.Point(pnt.X, pnt.Y, pnt.Z) length += get3DLength(pnt, pnt_prev) pnt_zm = arcpy.Point(pnt.X, pnt.Y, pnt.Z, length) part_zm.append(pnt_zm) pnt_prev = arcpy.Point(pnt.X, pnt.Y, pnt.Z) cnt += 1 lst_poly_zm.append(part_zm) polyline_zm = arcpy.Polyline(arcpy.Array(lst_poly_zm), sr, True, True) return polyline_zm def get3DLength(pnt1, pnt2): return math.sqrt((pnt1.X - pnt2.X)**2 + (pnt1.Y - pnt2.Y)**2 + (pnt1.Z - pnt2.Z)**2) if __name__ == '__main__': main()
So the script creates two lines, the first is 2D (no Z) and the second has the same shape but the sides have an angle of 45° in Z direction, which mean that they are root(2) longer as shown in the field Length3D:
If you look at the lines in 2D they look the same, but the (3D) length isn't:
When you want to get the point at a distance of 2500m from the start in 3D the result should be:
... or looking at it in 3D:
The alternative would be to use dynamic segmentation on the M-aware polylines.
