Latest Contributions by MelindaMorang1

‎05-20-2012

That is super annoying. That's what I was trying to avoid. A points layer in a projected coordinate system has a geographic coordinate system with lat/long underneath, right? For that reason, I don't see why there isn't a way to get lat/long even if the data is projected.

‎05-19-2012

As part of a longer script I'm writing, I need to add fields to my points layer and put the lat/long coordinates in those fields. This is so EASY to do manually by opening the attributes table, adding the fields, and doing a "Calculate geometry." There's an option to tell it what units you want. I keep trying to find a way to do this with python geoprocessing, and I can't figure it out. I was using AddXY_Management, but this only yields the X and Y coordinates in whatever projection my points layer happens to be in. CalculateField_Management won't let me specify the units for a points layer (or if it does, I can't figure out how). Anyone know how to do this? I feel like it should be easy and I'm just missing the magic python command.

‎04-23-2012

I'm creating a very large OD cost matrix using Network Analyst. Weird things are happening, and I'm wondering if I'm hitting some sort of maximum file size limit. Is there a maximum file size or number of rows allowed in the lines sublayer for an OD cost matrix? For that matter, is it true that the size of shapefiles is limited to 2Gb because of the limitations on the dBase format? Finally, I feel like this should be a really simple question, but I can't seem to find the answer anywhere in the documentation. What type of file is a network analyst layer and/or network analyst class? Is it some sort of geodatabase, or would the sublayers be subject to the same limitations as the shapefiles? Thanks!

‎04-20-2012

To clarify: It's not a web service. It's a downloadable custom ArcToolbox script tool created with python. The ultimate goal of the tool is to be able to figure out the area reachable by walking and transit from a given point. To do that, you need to know the network distance between that point and the transit stops you could walk to within the time limit. However, you also need to know the network distance between the transit stops themselves. Someone might, for instance, walk for one minute to get to a stop, get on the bus and ride for 10 minutes, get off the bus and walk for 5 minutes to another stop, and then get on a different bus and ride some more until the time runs out. So, we also need to know the stop-stop network distance to calculate how long it takes to walk between stops. We solve this problem by just calculating one big OD matrix for all the stops, within a cutoff distance. We've separated this part of the tool so you only need to do it once for any city, and you can calculate many different service areas without having to run the long part over and over. The OD matrix just sits in an SQL table that the code can refer to.

‎04-20-2012

Actually, what I'm doing is creating a custom tool to let people create walking/transit service areas using GTFS public transit data. See http://www.transit.melindamorang.com/ for more details. If I were just doing a single analysis myself, it would make sense to break up the data into chunks, but I don't think that would be practical for a tool used by a variety of people for a variety of datasets. Currently the tool simply allows the user to enter a cutoff distance for the OD matrix to keep the file size down, but they have to make sure to use a cutoff distance greater than the maximum distance they expect their pedestrians to walk when they're calculating their service areas later. It works fine, except for the output file size with a large transit network and a cutoff distance larger than, say, a mile. Is ESRI working on incorporating a way to use GTFS data into Network Analyst? To me, NA's public transit capabilities seem really lacking. There's definitely room for improvement, and I'd love to see it be able to handle GTFS. Because GTFS datasets are used in Google Maps trip planning, transit authorities actually keep them up to date and readily available, unlike transit-inclusive network datasets. Plus, they actually have schedules, and the schedules make a huge difference as far as what areas are accessible and what aren't.

‎04-20-2012

Thanks, Jay. My hierarchy is set to "NO_HIERARCHY" since I don't really need it for anything. Although, come to think of it, I was wondering if there was a way to use it to prevent pedestrians from walking on limited-access highways for network datasets that don't have anything like that in the restrictions. But that's another topic... I'm trying to calculate an OD matrix of bus stops in Chicago. Since there are nearly 13,000 of them, it's obviously not practicable to calculate an OD matrix for the entire network. However, even a matrix with a cutoff distance of 1.5 miles creates an output file on the order of several Gb because the network of stops is so dense. I'd love to be able to cut that down.

‎04-16-2012

Hi! I'm creating OD cost matrices of walking distance between transit stops in Chicago. So, because my origins and destinations are the same files and because pedestrians don't care about one-way restrictions, the distance from Stop A to Stop B is always equal to the distance from Stop B to Stop A. Is there a way to cut down the analysis time and output file size by having Network Analyst calculate the distance between A and B only once, instead of twice (A->B and B->A)? Thanks! ~Melinda PS. I have already cut down the run time and output file size by using cutoff distances. Still, when your cutoff distance is 2 miles, it still takes forever and results in a very large output file.

‎03-13-2012

You can either assign a single except routine to multiple named exceptions, or different except routines to different errors. Thanks, mdenil! That makes sense, and I have no idea why I didn't think of that myself. What's the syntax for the particular error I'm looking for? I know there are several reasons I could get an "ERROR 030024" I'd want the code to fail for anything other than "No solution found."

‎03-12-2012

I've created a custom tool using python geoprocessing, and it contains a bunch of Network Analyst tools. At one point in my code, I calculate an OD Cost Matrix and then use the results to do other stuff. However, it is conceivable that the OD Cost Matrix could yield no results, which leads to a "No Solution Found" error. <class 'arcgisscripting.ExecuteError'>: ERROR 030024: Solve returned a failure. No solution found. Failed to execute (Solve). The tool then crashes and exits. However, when this case occurs, I'd rather simply alert the user and then have the tool continue the analysis in a different way. So I want to include a logic statement. However, I can't figure out how to actually talk to this error message/exception within python. How do I code something that does this: if ("No Solution Found" = TRUE): Do this... Thanks!

‎02-14-2012

ArcScene crashes every time I try to export a TIN to .wrl also, and I would love to know how to get around this problem. I was able to export a simple raster file from ArcScene to .wrl, but even that took forever and crashed a few times before it worked. Also, even with the slider for jpg image quality all the way up, the jpg file for texture is very low resolution, not really good enough for what I want to do.

‎12-26-2011

Hi everyone. I've been working on this exact same problem and have developed a tool that allows you to calculate walking/transit service areas using Network Analyst and GTFS data. Check out http://transit.melindamorang.com. A beta version of the tool will be available for download within the next few weeks, and I'd love to get your feedback and ideas for improvement.

‎12-19-2011

Many thanks to all of you. I had this exact same problem, and the solutions listed here worked perfectly for me.

‎11-09-2011

I'm trying to figure out how to grab and manipulate Network Analyst output sublayers using python. For instance, I've successfully run an OD cost matrix calculation using python geoprocessing. I get the "Lines" output sublayer. This is probably just a stupid problem, but I can't seem to figure out how to work with the Lines sublayer (or just what the syntax should be to refer to it) in python after I create it. I want to: - Create fields in the Lines layer corresponding to my unique stop ids that I put in the origin and destination sublayers and then join the Lines layer to the origin and destination layers so I can grab the stop ids. - Export the Lines layer attributes table, including the new fields with the stop id, to a csv I can do all this by hand, but I want to do it in python, and I'm really stuck. Thanks.

‎11-06-2011

I'm trying to figure out how to grab and manipulate Network Analyst output sublayers using python. For instance, I've successfully run an OD cost matrix calculation using python geoprocessing. I get the "Lines" output sublayer. This is probably just a stupid problem, but I can't seem to figure out how to work with the Lines sublayer in python after I create it. I want to: - Create fields in the Lines layer corresponding to my unique stop ids that I put in the origin and destination sublayers and then join the Lines layer to the origin and destination layers so I can grab the stop ids. - Export the Lines layer attributes table, including the new fields with the stop id, to a csv I can do all this by hand, but I want to do it in python, and I'm really stuck. Thanks.

‎11-02-2011

Is there a way to do this with python geoprocessing? This is probably just a stupid problem, but I can't seem to figure out how to work with the Lines sublayer in python after I create it. I want to: - Create fields in the Lines layer correspinding to my unique stop ids that were in the origin and destination sublayers - Export the Lines layer attributes table, including the new fields with the stop id, to a csv I've figured out how to calculate the OD Matrix in python, but after it's created, I can't figure out how to do anything with it in python, although I'm able to manipulate it by hand from ArcMap. I'm really stuck.

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Latest Contributions by MelindaMorang1

Re: Calculate geometry (lat/long for a projected points layer) with python geoprocess

Calculate geometry (lat/long for a projected points layer) with python geoprocessing

Maximum file size for network analyst layer and/or network analyst class?

Re: Economizing OD Cost Matrix when A->B = B->A

Re: Economizing OD Cost Matrix when A->B = B->A

Re: Economizing OD Cost Matrix when A->B = B->A

Economizing OD Cost Matrix when A->B = B->A

Re: talking to arcgisscripting.ExecuteError in custom python tool

talking to arcgisscripting.ExecuteError in custom python tool

Re: ArcScene crashes with TIN

Re: Trying to incorporate a GTFS route sequence into service area analysis layer

Re: Tool validator - required field starts as error

How to access Network Analyst output sublayers using python

How to access Network Analyst output sublayers using python

Re: Solve OD cost matrix �?? Compute new field in « Line » objects table