Hello,
I'm trying to select polygons from a feature class using a polyline feature class.
See below for an example that shows the type of feature class/general concept I'm dealing with:
I don't want to have all three polygons selected, just the two with the blue dots. My end goal is to export the selected polygons so that I can merge them into a one large polygon.
It doesn't seem like there is a Select By Location method that can isolate the polygons I'm interested in (again, the two that contain dblue dots). I tried "Append" on the two feature classes (first had to convert polygons to lines) and then used "Trim Line". That worked to get rid of the dangle, but I couldn't get a line feature back that could be used for the purpose I wanted in Select By Location.
Also, I tried Integrate to change the line to get it inside just the two Polygons of interest (so I could then use it to select the two polygons instead of having all three polygons selected), but that was a bit too messy for the actual feature classes I have. In other words, the line feature didn't modify in predictable way that would be helpful to use it in Select By Location.
Thanks for your help,
- Josh
Accepted Solutions
Another way to solve this is to use two Select By Locations. For example, one could use Select By Location to find the parcels crossed by the lines, then save that selection out as a new feature class, then run the second Select By Location comparing the output from the first one to the points.
Using Select By Location—Help | ArcGIS for Desktop
Chris Donohue, GISP
Depending on the precision of your data you could accomplish this by doing several steps. You could create a point featureclass from the line, creating points for "BOTH_ENDS":
And apply a small buffer to those points to make sure that we can distinguish the end points that area really located within a polygon and not on the outline.
The first step would be to select those polygons where the lines intersect the polygons:
This will select all 3 polygons. Then you will remove polygons from the selection that completely contain the buffered end points:
To end up with this:
You could also use some python code and intersect each polygon outline with the line and count the resulting points (2 gets selected and 1 not).
As an example snippet how this could be done in Python:
def main():
import arcpy
fc_poly = r'C:\GeoNet\SelectPolygonByLine\data.gdb\polygons'
fc_line = r'C:\GeoNet\SelectPolygonByLine\data.gdb\line'
polyline = arcpy.da.SearchCursor(fc_line, ('SHAPE@')).next()[0]
fid_set = []
with arcpy.da.SearchCursor(fc_poly, ('SHAPE@', 'OID@')) as curs:
for row in curs:
polygon = row[0]
oid = row[1]
outline = polygon.boundary
result = polygon.intersect(polyline, 1)
if len(result) == 2:
fid_set.append(oid)
fld_oid = arcpy.Describe(fc_poly).OIDFieldname
where = '{0} IN ({1})'.format(arcpy.AddFieldDelimiters(fc_poly, fld_oid), ', '.join(str(a) for a in fid_set))
print where
if __name__ == '__main__':
main()When using this situation (label of polygon is OBJECTID):
This will yield a where like:
OBJECTID IN (1, 2)When I apply this to the polygon layer, you get this result:
But all depends on the precision of the data...
Thanks for your help and creative idea Dan. I tried your suggestion but I did not get the results I wanted unfortunately. I think I oversimplified my features in the drawing. Essentially, there are cases in which dangles represent actual features (in other words, there are features that don't completely cross the polygons that I need to keep).
Here are two examples of actual data I'm looking at:
1) I want to select and keep the polygons with a red X. Polygons with a blue X will be incorrectly selected using my current methodology, since the polyline and polygon precision is different:
2) Here's an example of a dangle I'd like to use to actually select an underlying polygon. I want to keep all polygons in this picture but to make it easier to distinguish, I put a Red X in the polygon with the dangle:
Does that give you a better idea of what I'd like to accomplish? In any case, it's a fun problem!
Thanks again,
- Josh
