Created
January 17, 2016 21:35
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Get sum of change in degrees between the 2 line segments in every trigram of points in a LinestringZ as proxy for curvature.
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select | |
ogc_fid, | |
sum(degrees(atan2(opposite, adjacent))) as delta_degrees | |
from | |
(select | |
ogc_fid, | |
point_idx, | |
st_3ddistance(unit_tangent_endpoint, unit_vector_endpoint) as opposite, | |
st_3ddistance(common_point, unit_vector_endpoint) as adjacent | |
from | |
(select | |
ogc_fid, | |
point_idx, | |
point_2 as common_point, | |
st_setsrid( | |
st_makepoint( | |
st_x(point_2) + ((st_x(point_2) - st_x(point_1)) / st_3ddistance(point_1, point_2)), | |
st_y(point_2) + ((st_y(point_2) - st_y(point_1)) / st_3ddistance(point_1, point_2)), | |
st_z(point_2) + ((st_z(point_2) - st_z(point_1)) / st_3ddistance(point_1, point_2)) | |
), 2852 | |
) as unit_tangent_endpoint, | |
st_setsrid( | |
st_makepoint( | |
st_x(point_2) + ((st_x(point_3) - st_x(point_2)) / st_3ddistance(point_2, point_3)), | |
st_y(point_2) + ((st_y(point_3) - st_y(point_2)) / st_3ddistance(point_2, point_3)), | |
st_z(point_2) + ((st_z(point_3) - st_z(point_3)) / st_3ddistance(point_2, point_3)) | |
), 2852 | |
) as unit_vector_endpoint | |
from | |
(select ogc_fid, point_idx, point_count, | |
st_transform(st_pointn(geom, point_idx), 2852) as point_1, | |
st_transform(st_pointn(geom, point_idx+1), 2852) as point_2, | |
st_transform(st_pointn(geom, point_idx+2), 2852) as point_3 | |
from | |
(select ogc_fid, st_numpoints(wkb_geometry) as point_count, | |
generate_series(1, st_numpoints(wkb_geometry)-2) as point_idx, wkb_geometry as geom | |
from vermont.roads | |
where | |
tnmfrc < 4 | |
and st_numpoints(wkb_geometry) >= 3 | |
) as points | |
) as point_3tuple | |
where st_3ddistance(point_1, point_2) > 0 and st_3ddistance(point_2, point_3) > 0 | |
) as unit_vector_endpoints | |
) as tan_components | |
group by ogc_fid |
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