How to densify LineString vertices in Shapely/GeoPandas

Question

I'm looking for an equivalent of densify tool in ArcGIS, but with GeoPandas or Shapely. I have a line that would like to be densified with a specific distance; how to add vertices of a line using Python?

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Suppose I have a line that has 2 vertices (WKT) LINESTRING (0 0, 9 0). how do I divide the line into an equal distance of 1 such that it returns the same line, but with instead of 2 vertices, it has 10 vertices? the result I expect:
LINESTRING (0 0, 1 0, 2 0, 3 0, 4 0, 5 0, 6 0, 7 0, 8 0, 9 0). I find this post which is similar to what I want, but it uses ArcGIS instead of GeoPandas and Shapely.

Answer 1

I crafted a function for you. Here is your line, which I call old_line:

old_line=LineString([(0,0), (9,0)]) # your line with 2 vertices

Here is the function that takes a line geometry as main input, you assign a step (i.e the spacing along the old line) and and additional Coordinate Reference System (crs) to georeference the new densified line.

   def densify_geometry (line_geometry, step, crs=None):
        
        # crs: epsg code of a coordinate reference system you want your line to be georeferenced with
        # step: add a vertice every step in whatever unit your coordinate reference system use.
    
        length_m=line_geometry.length # get the length
    
        xy=[] # to store new tuples of coordinates
    
        for distance_along_old_line in np.arange(0,int(length_m),step): 
    
            point = line_geometry.interpolate(distance_along_old_line) # interpolate a point every step along the old line
            xp,yp = point.x, point.y # extract the coordinates
    
            xy.append((xp,yp)) # and store them in xy list
    
        new_line=LineString(xy) # Here, we finally create a new line with densified points.
        
        if crs != None:  #  If you want to georeference your new geometry, uses crs to do the job.
            new_line_geo=gpd.geoseries.GeoSeries(new_line,crs=crs) 
            return new_line_geo
    
        else:
            return new_line

Now, running:

densify_geometry(line_geometry=old_line, step= 0.5, crs= 32754)

returns:

LINESTRING (0.00000 0.00000, 0.50000 0.00000, ...
dtype: geometry

If you want to .apply it to a whole GeoDataFrame geometry column:

kwargs_dict={'step':0.5,
             'crs':32754}

your_gdf["new_geometry"]=your_gdf.geometry.apply(densify_geometry, kwargs=**kwargs_dict)

This should do the job.

Answer 2

I'm late to the party, but for future reference, Shapely now has this as a builtin feature called segmentize().

Just pass in a linestring geometry and the maximum segment length that you want to see. Requires GEOS >= 3.10.0

line_geometry = loads(
    "LINESTRING (-122.341611276025 47.6821613269801,-122.341891356399 47.6824837063215,-122.342138308987 47.6827979735732)")

new_line = shapely.segmentize(line_geometry, 0.0001)
# Output:
# LINESTRING (-122.341611276025 47.6821613269801, -122.3416672920998 47.68222580284838, -122.34172330817461 47.68229027871666, -122.3417793242494 47.68235475458494, -122.34183534032421 47.68241923045322, -122.341891356399 47.6824837063215, -122.341953094546 47.68256227313442, -122.342014832693 47.682640839947354, -122.34207657084 47.68271940676028, -122.342138308987 47.6827979735732)

https://shapely.readthedocs.io/en/stable/reference/shapely.segmentize.html