The Web Duel: part 3, Open Source

The Open Source Implementation

This is a continuation of Mark Balwanz’s blog posts on his creation of web mapping sites using both ESRI and Geoserver.  Today he will talk about his experience creating the site using open source technology.

After completing the ESRI version of my project (Web GIS Duel: Part 2), I turned my attention to the open source version of my project.  I have some experience with Open Source GIS from previous graduate courses and have spent some time working with Leaflet in the past, but this project was definitely going to be a learning experience for me.   Below you will find a list of all the technology I used to create this web mapping application.

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Open Source GIS Course at UMD – the Syllabus

UMD provided me with enrollment numbers, and we are getting a pretty full class.  However, a few people on the “outside” have asked for a little more depth into what will be covered.  So, I put together a quick outline on each of our class meetings.

Keep in mind, in addition to the class meetings, there will be weekly discussions and short assignments.  Each class session is 2.5 hours long.  Those sessions colored orange are classes that I will be on the campus live (please note that this is tentative, and the dates may slide around a bit), giving the lecture and assisting students in the lab.  The other class sessions are a combination of online video lectures or in laboratory exercises.  For those with full time jobs, most of the material can be performed at home on you own devices, although being in the lab with the TA will be helpful.

Again, please feel free to email to get more information about signing up for the class. Continue reading

Upcoming course: GDAL

I am putting up a new course on about learning GDAL – and, it is going to be FREE.  I’ve been so happy with the uptake and positive responses by so many people who have signed up for my other courses that I wanted to give back to the community.

I should be done with the course in a few more days, but I wanted to show you one of the lessons on creating an ETL routine using ogr2ogr – I think this is really cool.  You can find a link to the lecture here.

SQL and ogr to create 4D lines

A friend recently asked me to help him generate polyline shapefiles with Z and M values that he could deliver to a customer.  The problem was, the software he was using supported the import of Z and M values, but did not support the export of those files.  The other problem was, he has zillions of data tables that he needed to export!

Fortunately, PostGIS allows us to create Polyline ZM data rather easily.  The next part was to figure out how to get it exported to a shapefile.  So, here goes:

Assume you have a table with 4 columns: lineID, Z, M, and geometry.  The geometry field is a point feature that represent vertices on a line.  The lineID separates all those points by which line they are part of, and the Z and M values are, well, Z and M.

Make the Polyline ZM

The SQL command to create a 4D line is:

SELECT  lineid, 
                         ST_Y(geometry), z, m)
            ) AS g
FROM zpts
GROUP BY lineid;

In this case, I am making a line (ST_MakeLine) as a series of X (ST_X), Y (ST_Y), Z, and M values.  Grouping the results of the query by the lineid allows me to create a line for each set of points. Continue reading