Open Source Work-flow for Surface Interpolation with Curvilinear Anisotropy

Michele Tobias, PhD

Geospatial Consulting @ UC Davis University of California Davis

FOSS4G Portland, OR Sept. 8-13, 2014

Question: How do you accurately interpolate depths for a meandering river channel?

Variable data density

Highly anisotropic

Variable anisotropy direction

Why Don't TypicalInterpolation MethodsWork?

IDW

Overview

Input Data

Straighten the River

Interpolation

Re-Bend the Estimate

Input Data

Depth Measurements

River Polygon&Reference Line Offset from River

Regular Grid over River

Made in QGIS

Straighten the River

Based on Merwade et al. 2005

CREATE TABLE points_sn AS

SELECTpoints.gid,points.bed_elevat AS depth,st_distance(line.geom, points.geom) AS N, st_line_locate_point(st_linemerge(line.geom), points.geom) * st_length(st_linemerge(line.geom)) AS S,points.easting AS X, points.northing AS Y,st_makepoint(st_distance(line.geom, points.geom), st_line_locate_point(st_linemerge(line.geom), points.geom) * st_length(st_linemerge(line.geom))) AS geom

FROM referenceline AS line, willamette_points AS points

In PostGIS: Transform the Depth Data

CREATE TABLE rivergrid_sn as

SELECT points.gid,st_distance(line.geom, points.geom) AS N, st_line_locate_point(st_linemerge(line.geom), points.geom) * st_length(st_linemerge(line.geom)) AS S,st_makepoint(st_distance(line.geom, points.geom), st_line_locate_point(st_linemerge(line.geom), points.geom) * st_length(st_linemerge(line.geom))) AS geom

FROM referenceline AS line, gridpoints AS points

In PostGIS: Transform the River Grid

Interpolation

In R or your favorite GIS

vgm.data