[GIS] Calculating Slope of Street Segments using ArcGIS Desktop

3d-analystarcgis-desktopslopespatial-analyststreets

Using a DEM, I need to assign slope to individual segments in a street centerline feature class. It will be used to account for increased travel time for steep slopes in a network analysis. I am using ArcGIS 10.0, ArcInfo license, with 3D Analyst and Spatial Analyst extensions available.

My initial attempt was to use the "Add Surface Information" tool. However, the resulting average slope values seem suspect in some areas, for example if a stream crosses the street segment. I would like to try assigning elevations to street segment endpoints then calculating slope. I have read about this method Calculating average slope along line using ArcGIS Desktop?) but need further details on the process.

Best Answer

If you do not care about what happens between your two ends (not that this is dangerous for long roads in hilly regions), here are the steps :

1) feature vertices to points (ask for START and for END)

2) extract values to points (for both sets of points, don't forget to check the "interpolate" box)

3) join by attributes (based on ID) the starts and the ends to your line

4) compute your "start to end" slope

Related Solutions

[GIS] Calculating average slope along line using ArcGIS Desktop

A simple approach that you could automate in ArcMap using Python would be to break your line into points at a chosen interval ~~or even just at the vertices~~. Then extract values to points from the raster to get the longitudinal profile (make sure to select the interpolation option). Then simply calculate the average value of those points.

As @whuber mentioned there is an accuracy trade-off with simplicity, but if you're looking for a simple solution that you could script quickly the above should help.

[GIS] How to find the watershed for each outlet point and sum values within it

Assuming that each withdrawal point is related to the closest stream segment, we can do the following:

Use the split line at point tool to split the stream line into segments based on outlet points (depending on your data you may already have this). Make sure that each point has an ID, which should relate to stream order (see one method below for an example in Python).
Use the generate near table tool to generate a table that will link your withdrawal points to the nearest stream segment. Check the only get closest checkbox so you only get one result for each point.
Join the withdrawal amout to the near table to associate with the segment IDs.
Use the summary statistics tool to sum the withdrawal amount grouped by segment ID.
Join the output withdrawal sums to your stream segment, select those segments upstream from the point of interest, and sum the total withdrawals (again, see below for one way to do this).

And example of IDing the segments using Python.

import arcpy

#Written assuming arcGIS 10
#Note this will require modification to run...

start_pts = {}
end_pts = {}

for segment in arcpy.SearchCursor("segmented_line"):
    start_pts[segment.SEGMENT_ID] = segment.SHAPE.getObject(0) #SHAPE returns an arcpy.Array
                                                               #object containing points for
                                                               #geom type line
    end_pts[segment.SEGMENT_ID] = segment.SHAPE.getObject(segment.SHAPE.count)

try:
    #cleanup as you can only have one cursor open at once, otherwise wackiness
    del segment
except:
    pass

rows = arcpy.InsertCursor("start_pts")
for start in start_pts:
    row = rows.newRow()
    row.SHAPE = start_pts[start]
    row.SEGMENT_ID = start
    rows.insertRow(row)

try:
    #more cleanup
    del row
    del rows
except:
    pass

arcpy.SpatialJoin_analysis(start_pts, outlet_pts, "start_outlet_pts",
                           "JOIN_ONE_TO_ONE", match_option="WITHIN_A_DISTANCE",
                           search_radius="some metres")

arcpy.JoinField_management("segmented_line", "SEGMENT_ID", "start_outlet_pts", "SEGMENT_ID", "OUTLET_ID")

################################################################################
##Repeat for end_pts
################################################################################

Once I get a bit of time later I'll come back and update this answer with a bit of script to build a network using networkx to help sum the values...

Hope this helps!

Best Answer

Related Solutions

[GIS] Calculating average slope along line using ArcGIS Desktop

[GIS] How to find the watershed for each outlet point and sum values within it

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