QGIS

20 minutes at the East TN TNGIC Meeting

rjhale · Sep 6, 2018 · Leave a Comment

I went through a year or so of not talking at conferences. For local ones I’d show up and do something. I taught a workshop at FOSS4GNA 2018. I did a workshop at FOSS4G 2017 in Boston (and it sorta sucked). I need to get out of that mode and talk more – but I’m happier being quiet these days and working with clients.

Anyway – at FOSS4GNA 2018 I discovered something – the OSGEO Suite had disappeared from Boundless’s Website and was replaced with a github repository. It wasn’t long after Don Meltz put up an excellent explanation of the OSGEO Suite. The OSGEO Suite being gone isn’t a problem. It does increase the amount of talking I have to do spend explaining it’s not a problem. I could even compile the suite – but my clients can’t. They are smart people – but the time to compile the boundless suite won’t be happening.

One of the things I keep running into is the idea of an Open Source Server. The OSGEO Suite was well known and I get people asking “Hey – can you set us up a geo server”. They mean the opengeo suite. I then launch into an explanation of what makes up a “geo server” and they go a bit blank and answer me “Yeah – one of those”.

So for the next bit I’m gonna be doing something like this:

I want to explain how this works to people. We’ve gotten a bit deaf by hearing “ArcServer” at every conference in TN as this one monolithic thing you have to install to make a web map…which really don’t need since AGOL appeared but…you want SDE and it’s not called that and you have two people editing but you need SQl Server but you don’t….

Anyway, QGIS/PostgreSQL/PostGIS I’ve installed multiple times and as of late I’m experimenting with geoserver and what it can/can’t do. I have no grand delusions of creating ‘Randy’s Open Geo Spatial Super Duper Server’. I want to get to the point where maybe mapserver is an option in this. So much to learn…so little time.

I suck at github – but I’ve been more active as I try to develop a skill set and get over the angst of pushing and pulling things. I’ve built a vagrant box to install PostGIS/PostgreSQL/Geoserver so I can have something to point at plus it gives me a starting point for an upcoming class I’m in the middle of building. The vagrant box isn’t pretty – I expect to change it over the next bit as it’s mostly pieced together from a lot of other people’s work (Coleman McCormick, Dave Smith, etc). It works though and I have everything but pgadmin 4 running in one spot. Which – I don’t think this is anywhere near “install this for a server” because this is mostly just for talking, training, and testing.

So why vagrant? Why not docker? I can gloss over vagrant faster at theses talks than I can docker. I have 16 minutes to draw diagrams and about 4 minutes to publish one piece of data: QGIS -> PostGIS -> Geoserver -> Leaflet.

Anyway – if you’re up for the possibility of a train wreck of a presentation come by the East Tennessee Meeting in Kingsport next week as I try to explain how this works and hopefully you get excited enough to install some or all of these components and do something cool with your data.

OSGEOLive 12.0

rjhale · Sep 6, 2018 · Leave a Comment

So for those of you going “HEY I WANT TO USE SOME OF THIS OPEN SOURCE SOFTWARE?”. Maybe you can’t install it locally…or maybe you have a spare machine laying around – there’s a way for you to do it.

Download the OSGEOLive image and run it as a virtual machine or boot your computer into the Distribution. It’s a Linux operating system with about 50 plus free and open source geospatial applications.

They put a ton of effort into releasing this as a showcase of the software in the OSGEO realm. So give it a run and test out software you have questions about.

Adding Triggers to Geopackage

rjhale · Aug 30, 2018 ·

In between work I get a chance to play around with software. I’ve been digging around postgis more and more these days trying to get a better understanding of what it will do or won’t do. It’s a never ending learning experience for me. Sometimes it pays off – the never ending tutorial left me suggesting we dump a database to a geopackage.

I’m great at using geopackage in sentences like “USE GEOPACKAGE” and “Hey – what do you think about geopackage?”. Since I’m actually officially using it I decided to do some digging. It’s a SQLite container. Since it’s a SQLite container I should be able to do some things with it – like…..

I can use the spatialite gui and throw SQL against it and change the tables.

While talking to another person the question started with ‘Well – why can’t we just do the data collection in geopackage?’. Which we did some back and forth and in some cases this would be acceptable vs doing a full postgis install.

So my first question is: Can I make a trigger in a geopackage? The answer is yes. For those of you who don’t know what a trigger does – it responds to some action in a database. In postgresql, I put multiple triggers in a database for a client. Some triggers calculate lengths and some areas and some make a note of who edited a feature.

After some digging I found the syntax and wrote a trigger for SQLite/Geopackage in the form of:

CREATE TRIGGER update_esn AFTER INSERT
ON addresses
BEGIN
update addresspoints set “esn” = (select esn from polygon where st_within(new.geom, geom));
END;

I used the spatialte gui to add the trigger. So if I pass this off to a client they can edit an address and have it automatically pull in the emergency service number. Magic? Eh – close enough for me.

While it’s not going to work for a multi-user situation (or will it – I’ve not investigated) – it works. So now I’m adding widgets to QGIS to aid in data collection.

Rolling out PostGIS/QGIS Part II: Load your data

rjhale · Jul 31, 2018 ·

I did it – I’m at Part II. I actually did it. Wooooooo. For some of you – this isn’t news – but – for some it will be.

For the Record – Part 1.

So you’re sitting with a client and you’ve documented and asked “WHY” so much they really want you to leave – it’s time to start loading their file based geodatabase into an actual database. Here’s where it gets weird for about 5 minutes. In those 5 minutes where you’re getting ready to load data you really need to look at your client (hopefully sitting with you) and go “OK – you’re no longer calling yourself a technician – you’re a database person now”. They flip. You attempt to calm them – but yes – database person. Which isn’t particularly appetizing but this pile of data you’ve been hoarding in flat files for a good bit is a geographic database.

Most of the database admins I know are actually weirder than I am – which says a lot. One of my most spectacular “butt chewings” as a federal employee was the one time I did something to an oracle database and broke it. The admin had a fit. So much so when the yelling stopped several people told me “it’s not you – he’s on medication for this type of thing – you know – oracle DBAs and all – it happens so don’t take it personally”.

If you search the internet using Google for “Load Data into PostGIS” here is what happens.

google results not using qgis database manager

To spare you some reading – the first return mentions shp2pgsql. Actually most of the returns on the search will mention this. So much so you might think “I’m going to dump this file based geodatabase out to a shapefile and load it”. Don’t. For the sake of not over explaining this part – open QGIS and use your browser to navigate to your file based geodatabase and QGIS will read it. Same with shapefiles. Same with about anything. If you’re leaving the land of file based geodatabases, as my client was, here we sit with a way out. Add that data to your map display in QGIS.

qgis screen

If you open the Database Manager in QGIS you can do quite a bit with the data. If you have PostgreSQL/PostGIS running (as we do) you can connect to it and import data. You don’t have to make a jump to shapefile then load your data. You can do it here. Reproject, define primary keys, and apply spatial indexes all from a user interface. With one click your data gets pushed into postgresql/postgis. For a lot of my clients and potential clients this is unknown magic. Your data will change just a hair. Lower case your columns for the love of all that’s good in the world. Apply spatial indexes. Document if something significant changes.

So go back to my second paragraph where I went “you are now a database person”. You’re taking all these flat files or flat tile structured things and making them interact with each other via Spatial SQL. Which – not that big of a deal if you’ve got a full enterprise commercial roll out of Something Something Server Enterprise. It is a huge deal if you’ve never been able to do that. You get a large set of tools at your disposal you didn’t have before – plus the tools with QGIS you’ve got something very flexible in the making. Go ahead and order those books you’ve been eyeing. Join a listserve or three and ask questions. I still suck at SQL – but less than I did a few years ago.

There are still a pile of things to worry over like ESRI’s subtypes and domains and projections. Maybe you’re projections aren’t right. Maybe there is raster loaded in this File Based Geodatabase. What about permissions? Editing? You’ve just upgraded your Geographic Information System from a bunch of files to a database. With great power comes great responsibility – so you need to jump back into learning mode.

………and where does that lead me – to Part III and “Hey why did my attributes turn into numbers you said this was just pushing a button?”

QGIS 3.2: Drive Down Lists aka Value Relation Widget

rjhale · Jul 13, 2018 ·

This is cool.

So – North Road ran a crowd funding campaign to get this into the core component of QGIS. There was a plugin – and to be honest I discovered that about the same time as the crowdfunding was announced. The campaign put the plugin into the core parts of QGIS.

What happens is you have pick lists that can change based on other values. Have a pipe? It can be made out of W, X, Y, and Z. Is it a Water Pipe? It can only be made of X and Z. Wastewater Pipes can only be made of W and Y.

I worked my way through setting this up – and it’s really not bad once you know how. Granted – had I listened to the above video more closely it would have made better sense starting out.

Here is my walk through. I have a point layer and that point layer has a type and a subtype. I stored this all in a Geopackage by the way. The type drives the subtype. So you pick A and you can only have red or blue. Maybe B is green and white. I made two tables to help with this process tableA is 2 fields: a primary key and a value. TableB has three fields: a primary key, a value, and a foreign key that relates back to Table A. From that you can see Type A can only have a value of Red and Blue. Type D can only be Black and Gray.

tables

Here’s where it gets a little bit fun. My point layer has two attributes of concern: type and subtype. Type will be A,B,C, or D. Subtype will be a range of colors that Match the Type picked. If you right click the layer and select attribute forms you can assign a form for data entry. In this case for type the key column is the primary key and the value is the type. Note the Widget type is Value Relation!

type widget

Lets looks at the subtype field. The key column is the Foreign Key (the part that relates it back to table A). The value column is the subtype. The magic is this – if you look at the filter expression:“fk” = current_value(‘type’) . Check it out Below:

subtype widget

The foreign key equals the value of the type widget. When you add a point you’ll see this (nothing crazy). The type drives the subtype.

BUT WHEN YOU USE IT:

So you have a drive down list. Utilities usage? There’s more functionality with this you can exploit through the field calculator and the widget lists. It’s another greater way to control your data editing. So don’t be lazy – create great data to drive your database.

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