Posts

QGIS plugin for computing raster statistics

I have been working with Raster files for a while (mainly CropsCape data), but I have migrated from GRASS GIS to Python a while ago and have not since looked back. Tools like Rasterio have made life much easier for Python programmers, but it is still hard for those who are not programmers to do a few types of analysis. One of these analysis is to obtain summary statistics and histograms for the raster portion enclosed in a given polygon or for each polygon in a given polygon (or multi-polygon) layer.

August 17, 2015 Read

Presenting AequilibraE to the open source community

The nice thing of being in a conference about open source software is that the mindset of the people there is very close to mine: The value is in the service, and not in the piece of software, and if everybody contributes to the software, everybody will have good free tools to use. I won’t bore anybody with the details, but if you want to see the presentation slides, you can get them HERE.

April 24, 2015 Read

The next step for AequilibraE: True multi-threading

When AequilibraE has launched a couple of weeks ago, it was already clear that using multiple CPUs would be a requirement for it in the near future. For software developed in Python, however, parallel computing is always a challenge due to the existence of the GIL, which prevents a single instance of Python of using more than one processor. (if you want to know more about the GIL, this presentation is excellent, but you have to keep in mind that most of what we do in AequilibraE is CPU bound).

December 30, 2014 Read

Introducing AequilibraE for QGIS

Back in January 2003 when I started my career in transportation planning as an intern at Logit, my main tools as far as software went were MS Excel and TransCad (sometimes Maptitude). I would do all the modeling in Excel/VBA and use Transcad for assignment and visualization, and would always rely heavily on the visualization as one of the ultimate sanity checks to be done before sending the results to the clients.

December 16, 2014 Read

Gravity distribution model in Python

WARNING: THIS CODE HAS BEEN DEPRECATED. FOR THE NEW STUFF GO TO https://github.com/aequilibrae/aequilibrae If you had looked at this blog before, you probably already realized that I am all for sharing knowledge and tools, rather than keeping everything to myself and feeding the bad habit people in our field have of re-inventing the wheel every single time. I had an example of the of lack of people sharing tools for transportation modeling very recently, when I had to calibrate some synthetic gravity models for research I am doing for IPEA (The Brazilian Economic Research Institute), in Brazil.

July 2, 2014 Read

Using Delaunay tringles to build desire lines

WARNING: This has now been fully implemented in AequilibraE, and is also available through its QGIS plugin. Since I first starting using TransCad (TCW 4.0 back in 2003) I always loved Desire Lines. It is easy and quick to obtain (as shown HERE) and it is one of the most important tools I use to understand OD matrices while getting acquainted with new data and/or new regions. Although excellent for many analysis, desire lines yield very poor maps when the number of filled cells in a matrix is too large, which is the case for our current transportation models with their many thousands of Traffic Analysis Zones (TAZs), so I saw myself using desire lines much less in the last couple of years.

February 9, 2014 Read

Using raster images to model commodities

This is a non-conventional post, as it is just the presentation I gave at SHRP2 (Freight modeling group) last October in DC. It was a really good conference and I was very happy to be part of that. My presentation can be downloaded HERE, and below you can find my extended abstract. ABSTRACT When working with freight planning, particularly commodity modeling, it is frequently a daunting task to find data sources, especially data disaggregated to county or less than county levels.

November 16, 2013 Read

Python's Traffic assignment module (All or Nothing)

WARNING: THIS CODE HAS BEEN DEPRECATED. FOR THE NEW STUFF GO TO https://github.com/aequilibrae/aequilibrae Lately, I have been dealing a lot with traffic assignment problems of several types, but mostly All or Nothing and user equilibrium in some not so large networks. It is true that I could use something like Cube or TransCad, but I find TransCad post-processing capabilities not ideal if you want to do some non-standard analysis and Cube is even worse, as the GIS interface is very slow (the whole rendering thing is much slower than TransCad).

October 18, 2013 Read

Calling TransCAD from Excel

One of these days my Ph.D. advisor, Prof. Michael McNally asked me if I knew how to access TransCad through another software, say MS Excel, and how difficult it would that be. I told him that it was actually quite easy and could share some examples, but I also thought that it could also make a good post. Once you are passed learning how to use TransCad and you are in actual “professional production mode”, you realize that doing things manually is just not feasible.

May 6, 2013 Read

Cube's log file

I already posted some stuff about CSFFM, and I still have a couple more to post (many more after TRB papers are submitted) and this time I’ll talk a bit about the network editing procedure we went over. We started to develop our network based on the previous version on the passenger model (from which we borrowed the network and which had a very poor documentation), and ended up having a late start on integration with the new version of the passenger model being developed by CamSys.

April 9, 2013 Read

Transcad video tutorials

As I already mentioned, I’m currently pursuing my Ph.D. at UC Irvine. Among the many activities I have there, I am the teaching assistant (TA) for CEE123, which is an undergraduate senior class created to teach the 4-step modeling process to senior undergraduate and graduate students. This discipline on 4-step modeling with a very intense (textbook) project to be done in TransCad, and I am the one teaching the students about the software (currently the 5.

March 26, 2013 Read

US Refineries

I already talked about CSFFM when I presented the seasonality analysis I made for agricultural products, but now the focus is on different parts of CSFFM. When working with freight modeling, often analyses use aggregate data like sector employment, GDP, number of firms and other statistics the Census provides. It becomes, then, an econometric exercise of finding the best set of variables and functional forms, where the concern is with (not so) fancy econometrics like Heteroskedasticity, endogeneity, significance, etc.

March 19, 2013 Read