QGIS

Offline Editing Plugin: TN911 Project

rjhale · Jan 15, 2021 · Leave a Comment

One of the weirder problems we had on moving the ESRI setup was editing the data. It wasn’t the normal “hey lets add an address” but it was tackling the idea of “We need to edit the data in the field”.

As it was explained “the way we did things” was to drag the data out in the field with the editor because they were running a simple Arcmap/FBGDB. Now that we had moved to a Postgresql database I wasn’t keen on people “carrying the data out”. I preferred they connect to the database and edit it like civilized folk.

That is a problem because the county is rural and connections are sketchy and all of that led back to the idea of “Take a copy of the data with you”. We had a mobile solution but nothing making my life easier.

There is a plugin that originally caused much angst and it is called the OfflineEditing Plugin. It’s seriously the most no-thrills thing you will find in QGIS.

At one point in the early stages we had a lot of errors and I couldn’t figure out why. We have an ID attached to each feature that never changes. The client had discovered the plugin and it would let you check data out and edit it and check it back in. Which was what we wanted to happen…..except back when 3.0 was brand new we had a lot of things change unexpectedly. I had a trigger setup that added the primary key to the features ID. So data would come out. Data would go in and between the triggers and functions the ID would change. To the client this looked like a great solution. The intern thought it was awesome. The guy watching things change in the database didn’t have much joy.

I’ve not touched it since 3.2 or 3.4 in QGIS was out.

I’m running a “beta” (3.17) copy of QGIS at the moment. So I built a quick database and decided to play. It checks your data out and you then have a seamless offline dataset stored in a geopackage (the original data is in a postgresql database). I check it out and edit and check it back….and……

It worked. ID’s were respected. Sequences were maintained. I added data and checked data in and Edit Dates and Edit Times were also saved (at the time of check-in). Since I checked the entire database out and checked it in things I didn’t work on received a new edit date. Which – I think there is a way around that but that goes beyond the 1 hour test today. Which – given the 2+ years since I’ve touched it this plugin may have been working fine for a bit.

So what does this mean? Well – you can take your laptop and check your data out and go into the field. AWESOME IT’S VERSIONED….well not in the way ESRI versions anything so you will overwrite some data if you aren’t careful. It does make this setup a little more flexible although I’d rather toss this into a mobile app and only worry about the things we need to worry about – in other words if you’re working on addressing in a neighborhood I only care about that neighborhood. Which means I’d probably split that data out – check it out – edit it – Check it in and then merge it into your original data. More work but safer. I like safe.

Overall – a much better experience with the Offline Editing Plugin this go around.

I’m making a Map: Location

rjhale · Dec 23, 2020 ·

I should write something. My last few “2020 in Review” posts aren’t working like I’d wish – so I sat down last night to make a map.

A map of what? Good question. I think in my every day attempts of databases and technical wizardry I lose sight of “I actually like maps” and I’m not the best at it. Given my background I should be better. I decided to make a series of maps on “things I like”: Canoeing, Hiking, Bike riding, etc. So my first shot is a canoeing map. A very simple map of something I like to do.

The location is easy – The start of the TN River Gorge. It’s a great 8ish mile paddle. Simple. Quiet.

My first thought was to do what I normally do and just drape things over a aerial photo. I’ve decided to make it a bit more fun and not go that route – This may end up being Black and White. I’m also going to stick to two sizes of paper in this series of maps. Either 8×11 or 11×17.

When you canoe this loop – you start north and head south and loop around an island and then head back north again. The first half is all upstream (heading south) and the last half is all downstream (heading north). Bonus it’s all NW-SE trending so it will need to be rotated.

I start building it in QGIS with some aerial imagery and Hillshades for fun:

QGIS Canoe Map setup

If I make a 11×17 layout it looks more like this because I’ve added 120 degrees of rotation:

QGIS canoe map setup

As I sat here I had a question. I scale it. I generally start to get an idea of “what” I want. I know the extent of the map but can I get the extent back into QGIS so I can start clipping things and not having to include 500 square miles of stuff for a map. I could just set up the boundary back into QGIS as delimited text (make points -> draw polygon). I could just “eye ball it” which is how I do about everything from Jeep repair to Home Repair.

For fun I searched the tool box and….Print Layout Map to Layer

I run that and……I know where my map falls in the main window. So I can buffer it and start clipping data.

Why even post….I had no clue this tool was even here. My next map (another canoeing map) will be a bit larger than 11×17 so I’ll nee to use Atlas to setup 2 to 3 pages. I now have the general extent for 11×17 at X scale, copy and past this boundary a few times, and rotate it to get the general layout locations I will need

Map 1 is well on it’s way to happening. This is a bit therapeutic and that’s something I need at the moment.

Drop Down Menus for the TN NG911 Server

rjhale · Dec 4, 2020 ·

The problem is I have too many options. Options are awesome except when you’re dealing with people inputting data and you only want them to do it one way.

QGIS has had the ability to build drop down lists for a good while and it’s a very flexible way to work. For those of you in ESRI land imagine Domains and Subtypes on Steroids. In earlier versions you had widgets and currently you have Attribute Forms.

If you have a data layer in QGIS (all my layers are coming out of PostgreSQL/PostGIS) just right click the layer and go to Properties. You’ll notice all your fields have a chance to be a “widget”.

QGIS Layer Properties

Addressing data is probably 90% picking existing attributes. You don’t want to get too fancy in making up new stuff. For instance – Street Type.

USPS Sample Street Types

I ran out of fingers and toes on counting the number of street types. For the TN guys they all get a ESRI File Based Geodatabase with this information spelled out as Domain tables. How do you do that here? QGIS gives you three ways to make this happen:

Unique Values sums up an existing data set and you can get a pick list of existing data. The good thing is you don’t have to do anything really to make it work and the bad is you’ll get Avenue and Avenew. Misspellings aren’t your friend.
Value Maps let you fill things out or import a CSV. So if you save this information in a spreadsheet you can import it in.
Value relations pulls from an existing table. So if you build a table with this information you can pull that in by first adding the information to your QGIS session and then pulling it into the widget.

In order to cut out down the options, I pre-built all the tables needed into the database. I add them into qgis, group them, and collapse the group because No one needs to see them. Yet. You can’t use a relation widget with the table being added to QGIS.

QGIS grouped items

Back to the Attribute Forms and this is the boring part. I want to select the type table and apply it to the type field using a Value Relation. The important part is the key and the value is the description of that attribute. Both things could be “type” but I chose to have a type and a description:

QGIS setting up Type

Go through and start setting up your Forms. What if you have a second person working on this?

Save your style to the database source:

QGIS saves a table in the public schema and everyone with the proper permissions and access is good to go. Plus you don’t have to touch everyone’s QGIS session…well much. Users still have to load the tables to get started but good clean directions should work. Of course this does make me still debate a plugin that does part of this for you.

What? Yeah – it’s that easy. Everyone working with drop down menus and making good clean data.

Modeling Part 2

rjhale · Sep 22, 2020 ·

Not being content with my last model….

I dove back in because I really need to name the points something because the forestry guys almost always use GARMIN GPS equipment. After sitting on this for a week the question became “How do I name everything” and get it to the point where the model handles 90% of it:

Name the point and since I’m exporting GPX the field has to be “name”
Perform some sort of field calculation to get a “pt1” for a name
Label it in QGIS because I really want to be lazy.

I found the rest of the tools to let me do this:

Add autoincrement field which gave me a 1 through X number
Field calculator let me name this ‘pt’ || “AUTO”
Set layer style

My Model now looks like:

Not to go over the additions in excruciating detail but three tools later and I have a functional point layer. My next question is can I slap this in github and share it – which I’m going to do shortly. Will this break the layer style? I’m not sure – but I can save this with a ton of notes for more development.

I’ve really ignored the functionality of the Processing Toolbox. This small dive into it has highlighted some sore spots I’ve had with the TN 911 address project. I get frustrated because I’m not the best in Python. The big problem I’ve had has been working through a few problems that are going to require some sort of interaction between the 911 address person and the database and I can’t do that part in SQL (I could – but it would create too much black magic). I can fix it with a model though.

Then all my python fears get a little bit better because all of this can be moved to python and I can pick at it.

My 10 to 15 minutes of point building are now down to 10 seconds.

Now to get them using something other than a Garmin GPS Unit – like their phones.

Modeling in QGIS

rjhale · Sep 9, 2020 ·

I should model more….but I don’t. You’re welcome.

Anyway – the last few weeks I’ve been boring you with tales of topology and now I’m going to bore you with tales of building a model. One of my longest running jobs has been in Forestry and that’s pretty much a set of repeatable processes. With the current lockdown I’ve been experimenting with client data and how to speed up some of what I’ve been doing.

QGIS has a modeler. In ArcGIS, Modelbuilder was probably a favorite because I’m always doing repeatable processes. Granted I’ve offloaded a ton of things to PostGIS BUT – wouldn’t if be cool if…..

The Forestry guys get a new property to look at and I usually do something clumsy to get it into QGIS. If it’s an inventory they go and walk it. They usually walk it at a certain interval so they call me and I:

Create a Grid using the Regular Points processing tool.
Manually Delete the points that fall too far outside the boundary
Name the points

This takes anywhere from 5 minutes to 15 minutes depending on the property and the how well we feel the boundary fits the ground. A simple model would look like this:

With the QGIS Processing Modeler you have to set up an Input before you can do anything. So my input will be a vector layer. I will drag the Regular Points Algorithm in and give it an output. If I double click Regular points I need an extent to draw the points. I’m going to set that to a model input. I give it a name and you can see how everything is starting to connect. I also give it some spacing which is 264 feet (which is 4 chains):

Not bad but not great:

but I need to clip it to the boundary……and assuming the boundary is wrong I probably need to clip include some points outside the boundary. I also don’t want to open the model every time and change the spacing. Soooooooo…..Lets get the the “Poof” Magic part:

What did I do?

Buffer the input property
Create a grid based on this buffered polygon
Extract the points from the buffered area
Create a new layer

That’s almost perfect. So 5 minutes down to this. Of course there are things I need to change like “what if they want an irregular cruise” that might be a 4×3 or a 5×3. I haven’t quite figured out numbering the points but I”m assuming I’ll stumble into it it shortly.

I haven’t used the modeler in quite a while but with some extra time I’m going to shrink some of my processes to as “quick as possible”. Probably play around with Python some but I don’t really have to – this works for what I need to do with some small adjustments.

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