[GIS] How to get polyline features from a raster file using ArcGIS 10.1？

arcgis-10.1arcgis-desktoplinepolyline-creationraster

I have a watershed accumulation file look like this： enter image description here

There are several white lines by visual, and I tried the raster to polyline tool and got this：
enter image description here

Are there better ways to extract polyline features from a raster file instead of creating an new shapefile and drawing lines by myself？

Best Answer

before you run the raster to polyline tool, you should set a threshold on your accumulation value in order to define the background to zero. This can be done in many ways, e.g. using "reclassify" or using map algebra ( something like : Con( flowacc > threshold , 1, 0) ).

Alternatively, you can use "stream to feature", with a background set to NoData using SetNull( flowac > threshold, flowacc )

Related Solutions

Clip Raster Using Polyline or Polygon in ArcGIS Spatial Analyst

Use Extract by Mask which:

Extracts the cells of a raster that correspond to the areas defined by a mask.

and specify your polygon feature class of the US as the mask.

[GIS] Creating Polyline from GML using PyShp

Matthias,

The pyshp syntax requires nested Python lists containing coordinates as floats. Your current approach is a string which simply looks like the syntax.

The quick, but not recommended, method would be to eval your string (very insecure):

linestr = "[[[-94,-49.1152],[-94.45451,-49],[-93,-49.30391],[-94,-49.1152]]]"
w.line(parts=eval(linestr))

The proper way would be to cast each coordinate pair to floats and append to a list:

coords=[["-94","-49.1152"],["-94.45451","-49"],["-93","-49.30391"],["-94","-49.1152"]]
line_parts = []
line = []
for x,y in coords:
    line.append([float(x),float(y)])
line_parts.append(line)
w.line(parts=line_parts)

Best Answer

Related Solutions

Clip Raster Using Polyline or Polygon in ArcGIS Spatial Analyst

[GIS] Creating Polyline from GML using PyShp

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