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If the street street traffic emissions affect both side parcels, that the buffered parcels are overlapped is correct and fit to your puepose; you need to calculate the emissions distribution weight for each parcel (in other word they share that emissions). If you only want assign this seg emissions for one parcel, you need to clean overlapped parcels or using another way to select one seg from overlapping lines. Another thoughts: 1.Clean up the polygon layer first, to eliminate/clean up the gaps between adjcent parcels, overlapped parcel portions, sliver parcels. 2.Buffering the parcel (lot) outlines (one direction) instead of buffering the parcel polygons. 3. You can buffer street network lines instead of buffering parcels (one or two of line directions buffering), then convert the buffered polygons to lines, intersect those lines to parcel polygons. 4.Join the street network attribute data to the parcel layer by using address field, then convert parcel polygons to outlines, select that line closest to the street as target line for this parcel. Thank you! I won't have time to go through this today but will have a go tomorrow. And in fact, you might have alerted me to a logical error in what I was trying to do (assigning the emissions from the same link multiple times). I might have to convert them to a load per area first and then weight that to the size of my parcels. I'll get back to you.
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07-25-2013
04:03 PM
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I don't see any problem in your data processing. You need to know how to summarize the field to get your result in your insected line feature class table. Thank you. I can do the summary statistics but the problem is in the output from the intersect operation. There should not be as many line segements (in 100s of cases they are identical) assigned to each of the buffer polygons as there are. This must be a result of the overlap of the polygons, as it works fine when I use the layer with the contiguous, i.e. non-overlapping land use parcels. In the latter case I get for example 6 line segments if three network links intersect with the parcel (3*2 spatially coincident lines for each travel direction of each link; these are from the model network, hence they have exactly the same location; in the real world, these wold be seperate lanes).
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07-25-2013
01:48 PM
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I would say that looking at your original lines that you needed to first dissolve the roads into continuous lines, then perform the buffer. That would smooth out the bends without slivers. I also noticed the parallel lines for freeways and offramps. I would handle them in a separate process. If you come up with something better for your data, share it. You are not the only person to face this kind of need with a road network. Thanks for the reminder. As far as dissolving the original lines goes, my problem/task is to maintain the individual segments of even the same roads as I am using traffic loads on the network to calculate emission loads for each segment. And the traffic and thus the emissions vary on different segments of even the same road (the data comes from a travel demand model). And my "work around" entails doing something completely different than my original plan as I came to the conclusion that I would not be able to solve the buffer/overlapping polygons problem. It has turned into a fairly lengthy process and I am not sure it would be much use to anyone unless they try to do more or less exactly what I am doing. I am happy to post it, though - just in case. By way of explanation: I am working with two network features. One is the centre line of the real world road network, the second is the simplified (and not always spatially coincident) network from a travel demand model, which contains the traffic loads for the road segments. I am interested in the emissions that are created within a certain distance of inhabited land parcels (i.e. ultimately the emission loads affecting people living in those parcels) selected links from real network that are within 300m of inhabited parcels: CandidateNetwork1 selected all of these that are "intersecting" with model network with a search distance of 300m (this is to try and bring the data from the model network together with the real network in some way): CandidateNetwork2 deleted all links from CandidateNetwork2, that do not have an equivalent in the model network from which traffic/emissions data could be transferred created 300m buffers around CandidateNetwork2 clipped the layer of inhabited parcels by CandidateNetwork2 (getting all inhabited parcels or parts thereof that are within the buffer distance of the real network) buffered the parcels by 300m intersected the clipped parcel layer as well as the buffer layer with the model network (thereby getting as close as I saw possible to correctly assigning traffic/emission loads from the model network to parcels that in reality are within the chosen distance of the real network) - on this last step, I ran into big problems with the buffer polygon/network intersect step, though - described in another post in this forum That's it for the work around (once I have worked out the intersect problem). Maybe it is of use to someone.
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07-25-2013
01:06 PM
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Richard, thank you for this detailed response. I have tried to run through your methodology but have ended up with slivers for example where the roads form bends. Also, when I dissolve the result of the first intersection operation, for some reason, not all the polygons in the junction areas are dissolved together. Again, this may be a function of the geometry, i.e. where junctions are not completely perpendicular, the polygons might not actually touch and thus not be 'recognised' as belonging together. I think with a different dataset, your suggestions could work, though, so I will definetely keep them in mind for future reference. For my current project I have decided to approach the problem somewhat differently, as my dataset is too large to correct all 'errors' by hand. Thanks again.
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07-25-2013
12:00 PM
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Just use the geo-processing tool "Merge", and selecting the layer containing the buffer polygons as the input. A simpler way is to merge them when created, using the buffer tool. Thank you. I tried that but I still end up with the same amount of polygons, which still overlap. And in the "Buffer" tool, the dissolve options only allow me to either create one single buffer polygon for the entire network (ALL option) or to dissolve by shared attribute values (LIST option), for which I do not have the right field to define just those polygons that overlap.
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07-08-2013
12:17 PM
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Hello, I have question regarding polygons created through a buffer operation. I created a buffer feature from a road network centreline file, which consists of multiple sections. Around intersections and highway ramps for example, this resulted in a multitude of overlapping polygons (one for each element/link in the network). Now I would like to dissolve/merge those overlapping polygons into one so that each interesection for example is assigned a single buffer area while I want to maintain those polygons along single stretches of road as discrete features. I include an image below which hopefully explains what I am trying to say. I have tried feature to polygon and intersecting the layer with itsef as well as a few other options but so far I have only succeeded in either creating one continuous buffer polygon for the entire network or generating a multitude of individual polygons for each area of overlap. I know that in editing mode I could select and merge specific polygons by hand but my network has over 23,000 links and checking them all for overlaps and editing those by hand seems, well, inefficient. I also thought about creating a topology but the only fixes available for overlapping polygons also seem to be to a) either delete areas of overlap, b) assign them to one of the participating polygons or c) turn them into new polygons (back to the multitudes). I am not worried about summing or maintaining attributes of the buffer polygons other than their location. I could probably implement a python script that does exactly what I need but would not be able to fiddle around with one to adapt it myself. Any helpul hints would be greatly appreciated!! Thanks, P.G. [ATTACH=CONFIG]25803[/ATTACH]
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07-08-2013
11:16 AM
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