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I would like to create centerlines for many glaciers I am doing work with in ArcMap. I feel like I have a conceptual model that could work but can't seem to figure out how to make it happen with the tools available. I have polygons for each glacier outline, and DEMs for elevation data.

My idea is as follows:

  1. Using zonal stats find max/min elevation for each glacier using the outline polygons
  2. Turn the max and min pixel into a point file
  3. Then find either a least cost path using the DEM between the max/min for each glacier(seems complicated) or find the path between the two points that lies in the center of either side of the polygon.

It's the last step I need help with.

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2 Answers 2

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This is workflow for single glacier:

arcpy.PolygonToLine_management("Glacier", "./OUTLINE.shp")
arcpy.InterpolateShape_3d("DEM", "OUTLINE", "./outline3d.shp")
arcpy.FeatureVerticesToPoints_management("outline3d", "./points3d.shp", "ALL")
arcpy.AddZInformation_3d("points3d", "Z")
arcpy.Sort_management("points3d", "./sorted.shp", "Z DESCENDING")
# select extreme points
arcpy.SelectLayerByAttribute_management("sorted", "NEW_SELECTION", '"FID" in ( 0, 772)')
arcpy.SplitLineAtPoint_management("OUTLINE", "sorted", "./threeOrMore.shp", "0.5 Meters")
# set environment extent to glacier
arcpy.gp.EucAllocation_sa("threeOrMore", "./alloc", "", "", "5", "FID", "", "")
arcpy.gp.FocalStatistics_sa("ALLOC", "./fstat", "Rectangle 3 3 CELL", "RANGE", "DATA")
arcpy.gp.Thin_sa("fStat", "./thinned", "ZERO", "NO_FILTER", "ROUND", "50")
arcpy.RasterToPolyline_conversion("thinned", "./Skeleton.shp", "ZERO", "0", "SIMPLIFY", "VALUE")
arcpy.Clip_analysis("Skeleton", "Glacier", "./clipped.shp")
arcpy.SelectLayerByLocation_management("clipped", "INTERSECT", "sorted", "10 Meters")
arcpy.Dissolve_management("clipped", "./c_line.shp", "", "", "SINGLE_PART")

enter image description here

It's enough to create a loop through individual features to achieve your goal. You still need to decide what to do with holes in polygons caused by nunataks.

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GLARE toolbox created by bunch of authors have option for glacier flowline creation, it is called there "Trunk Stream Tool".

enter image description here

The inputs are:

  • Moraine - Frontal or lateral moraines that indicate the lower limit
    of the glacier
  • Zone Field - Field in the moraine feature class that
    identifies different features
  • DEM
  • Min Flow Accumulation (optional) - Minimum number of pixels from which water upstream would flow to consider a point as part of a stream
  • Output File Name - Name and storage for the resulting flowline
  • Output watershed (optional) - Name and storage for the resulting watershed

enter image description here

Here is a full information and article about the toolbox:

Ramón Pellitero, Brice R. Rea, Matteo Spagnolo, Jostein Bakke, Susan Ivy-Ochs, Craig R. Frew, Philip Hughes, Adriano Ribolini, Sven Lukas, Hans Renssen - GlaRe, a GIS tool to reconstruct the 3D surface of palaeoglaciers - Computers & Geosciences, Volume 94, 2016, Pages 77-85, ISSN 0098-3004.

sciencedirect.com, researchgate.com

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