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Hi Jay, My aim is to create 500, 1000, and 1500 m street networks buffers around centroids of origins (facilities located at a certain distance from the street network). Therefore, based on your advice, I will first use Calculate Location having Facilities as Origins to get the distance from the centroid of the facility to the nearest network point. Second, I will create the OD matrix for distances between the nearest network point of origins (facilities) to the nearest network point of destination (population points). Third, I will use NEAR to get the distance from the nearest point of destinations to the centroid of population point. Finally, I will add these three distances and then extract the 500, 1000, and 1500 m distances. Does that sound right? Thank you so much for responding so quickly! Have a nice day! In that case I will suggest that you use the Closest Facility solver instead of the OD. Use the Origins as Incidents and the Destinations will be Facilities and make sure on the Analysis Settings to set the Facilities to Find to the total number of destinations you have. You should be able to map the "distance" to the Attr_Length on both facilities and destinations. Jay Sandhu
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11-02-2011
08:06 AM
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Hello again, I am writing again about the issue I described above. I used the GP tool and calculated locations for the origins. I did the same for destinations. However, when I try to create the OD matrix, the "distance" field is not shown in the Location Analysis Properties for destinations. Therefore, I can only specify that I need distance measured from the centroid of the origins (facilities) but there is no way to specify that I need distance measured to the centroid of destinations (population points). I am not sure what to do next. Any help would be greatly appreciated.
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11-01-2011
06:54 PM
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Hello again, I am writing again about the issue I described above. I used the GP tool and calculated locations for the origins. I did the same for destinations. However, when I try to create the OD matrix, the "distance" field is not shown in the Location Analysis Properties for destinations. Therefore, I can only specify that I need distance measured from the centroid of the origins (facilities) but there is no way to specify that I need distance measured to the centroid of destinations (population points). I am not sure what to do next. Any help would be greatly appreciated.
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11-01-2011
06:49 PM
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Thanks, Srirama, I will take your advice! hi, Ideally they should not differ. And yes, snapping distances are not added (as far as I am sure). Do you have problems with all the pairs ? If not, just have another look at your cutoff distance parameter in your settings for OD matrix. This should not be the reason, but just have a look. As the documentation suggests, OD matrix is a quick solver and does not take into account shapes. May be there are slight differences in the manual version and OD (batch) versions of the algorithms. I stand under correction. Probably you should quantify your differences. Are they always differ by same amount, same percentage, may be some peculiar network edge common to all your (error) paths.
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10-31-2011
09:05 AM
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Thank you so much Bsimarak and Jay for your prompt answers! I truly appreciate your help! Your answers are very helpful Jay, thank you for providing me again with the right solution! I will take your advice. Have a nice day! The OD and all Network Analyst solvers find paths from the location where they snapped on the network. If your point is 30 meters away and you solve on travel time, how do you add the 30 meters to the travel time. So the total path length (in attribute units) is always on the network. It has nothing to do with the CUTOFF which is used to limit how far away you want to compute the distances too. Where does the documentation suggest that OD does not take into account shapes? The OD solver and all the Network Analyst solvers compute distances on the actual network. The only thing OD does not return back (for performance reason) is the actual geometry of the path taken. The OD is used when all you want is the network distance and do not care to see the path geometry. So to answer the original post, OD returns back distances on the network. If you want to add the snapping distance, then first use the GP tool Calculate Locations on your points. This will add the network location fields and also the x,y of the snapped point and distance to the network edge (make sure your projection is set to return the same distance unit as what you are solving on so that you get miles from edge if you are solving to minimize miles or you can convert it later with field calulator). Now create the OD layer and when you do load location, use the network location fields AND map the distance to the Attr_Length (or what ever the name of your distance attribute is). Now when you solve, the distance to the network will be added to the path length returned back after the solve. Jay Sandhu
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10-31-2011
08:28 AM
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Hello everyone, I created an OD matrix for distances between facilities and population centroids. Neither the facilities nor the centroids are located on the street network, but some distance away (e.g., 50-200 m). When I manually verify the distances I obtained in the OD matrix, I get values that are close, but not identical to the values from the matrix. I am not sure how are these distances being calculated? Are they measured from the point on the network that is nearest to the facility to the point of the network that is nearest to the centroid only? I believe the additional distances to the facilities and centroids (the so called "snapping distances") are not considered, is that right? My points layer and my street layer are in the same projection. Thank you!
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10-30-2011
09:48 AM
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Hi Jay, Thank you so much for your detailed answer. This is really helpful! I will use a trim value of 25 m. Thanks again!
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10-04-2011
09:28 AM
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I believe that this is going on because some facilities are located further away from the network (e.g., 200-300m from the nearest network location) so a service area of 400 m for one such facility would start from that network location on, away from the facility. Any thoughts about this?
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10-03-2011
08:52 PM
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Hi there, I am trying to create service areas for 1000 facilities for a break of 400 m. Everything works fine, but I noticed that several facilities have service areas that do not contain the facilities themselves (really weird). I should note that these facilities are located further away from the street network. I used the default tolerance of 5000 m and I selected the "detailed polygons" option with a "trim value" of 100 m (it is not clear to me what that "trim" value refers to). Does anybody know what I am doing wrong here? Thanks!
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10-03-2011
03:35 PM
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Hi everyone, I have the following issue: I have a street file and I need a point file that contains each intersection and the valence of each intersection. For example, an intersection of three streets will have a valence of 3. I used to be able to use the Calculate Fnode Tnode 2.0 extension by Juan Solorzano, but it does not work with ArcGIS 10. Therefore, I came up with this solution instead: 1. I used the "intersect" function and used my street file as input. I specified I need a point file as an output. I obtained a point file with all intersections. For each intersection I obtained a set of overlapping points that correspond to the number of arcs which intersect there. For example, if three arcs intersect there, I would have three overlapping points. Thus, the number of overlapping points would indicate the node valence for that intersection. 2. I used the "Collect events with count rendering" function from Spatial Statistics to get a table indicating how many overlapping points are present in each intersection (that is the valence of that intersection). I checked randomly and it seems OK. My question is: does this sound like a sound procedure to determine node valence? Am I messing up somewhere? Thank you so much for taking time to make sense of my post, M
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01-21-2011
11:11 AM
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