rjhale

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.

A tale of two FOSS4G meetings

rjhale · Aug 16, 2018 ·

In the Spring of 2017 I had a small FOSS4G meeting in Knoxville TN and the general feeling after it finished was “When are we doing this again?”. So the conversation started and surprise – we had two meetings.

The first meeting happened in Knoxville on August 13th 2018. We had 9 presentations. The big headache I had with this meeting is it all comes down to sponsorship. I wanted it cheap – but I didn’t want to do in the hole again to do this. So we had sponsors. We also had a $10 dollar charge that could be offset with a scholarship if needed.

We had right around 50 people and covered everything from postgis tricks to measuring vegetation in the Great Smokey Mountains with LIDAR.

The second meeting was in Huntsville Alabama on August 14th 2018. The GIS Association of Alabama stepped forwarded and covered all the expenses. There was no charge for this one.

Fifty people came from the North End of the State to hear about QGIS, working with FOSS4G tools, and Jupyter Notebooks.

So what is the point? Actually is there a point? I sat around most of the day playing with how I wanted to summarize these two meetings. Meetings like this are hard. You have catering, a worry no one will show up, and a bigger worry no one will come and speak. We gave close to 100 people a chance to see something different. Which was double of what we did last year.

When I first started going to GIS meetings back in 1995 it was exciting. People would get up and speak and we’d all compare notes and figure out that we were all wrestling with the same problems. We were writing AMLS and buying workstations and digitizing old maps. Everyone had some sort of ESRI based user group. Maybe they were Intergraph. Maybe they had bought other software.

Flash forward to now and I’m consulting and not working for the Feds. User group meetings have morphed into these multi day extravaganzas that meet in your area…possibly not. You have to budget time and hotel reservations and it’s just a pain. So you end up not talking to your fellow geo people….or as we saw over the last two days people with specialties where geo is another trick in the bag. Of course there is twitter and slack and facebook and linkedin and 100 different ways to talk to one another. What if you don’t?

So lets have a meeting centered around FOSS4G……or meetings. They don’t have to cost much. Maybe they cost $10 a person. Maybe they are free. For Knoxville I poured about 2 to 3 hours a week over the course of 3 months…so about 40 hours. It wasn’t that hard – get a few people together and it’s less difficult. Find a low cost/free location. Huntsville had theirs in a courtroom. Knoxville had theirs at the University.

So in 2018 – I would like to get people together to talk about FOSS4G. Maybe you have a friend with a commercial solution in place for his organization. Maybe they have nothing. I think ESRI owes a large part of their success from the early days of getting people together to talk. We can do the same for QGIS/PostGIS/Geoserver/GDAL/etc. It’s a big world out there – you can mix and match about everything. I may not be able to make a North America Meeting (FOSS4GNA). Maybe these smaller meetings can scratch an itch for people and I can do that instead.

There’s no one to tell me I can’t. So what am I going next year? Workshops and a meeting in Knoxville. It sounds like the same thing will happen in Huntsville.

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?”

2018 TN Eastern Regional GIS Meeting – September 13th 2018

rjhale · Jul 30, 2018 ·

This free forum is intended for GIS users and anyone interested in the GIS Profession.

September 13th 2018
8:00AM – 4:00PM
Eastman Lodge
Kingsport, TN

Event Details and Registration will be available at:
http://www.tngic.org/2018-regionals.htm#2018east

Keynote Speaker
Stacey Whaley – Sevier County GIS Director

Pre-Forum Classes September 12th , 2018
• Lidar Workshop (September 12, 2018, 1:00 PM – 4:30 PM) – Paul Dudley, State of Tennessee
• GPS Data Collection w/ Mobile Devices Workshop (September 12, 2018 1:00 PM – 4:00 PM) – Cliff Hoeffner, Duncan Parnell
• ESRI ArcGIS Pro Workshop (September 12, 2018, 9:00 AM – 12:00 Noon) – Ian Feathers, ESRI

Pre-Forum GeoCaching Event and Picnic Social September 12th , 2018

This Forum is Sponsored by TNGIC and hosted by NetGIS.

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.

rjhale

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