Field Papers

Field Papers

Advertisements

Installing QGIS 3 on Ubuntu 16.04

QGIS 3.0 is out and from the blogs and tweets, it looks awesome. Some one asked me how to install QGIS 3.0 on Ubuntu 16.04, so here are the steps.

First, if you have previous version of qGIS, lets delete that

sudo apt-get autoremove qgis

sudo apt-get --purge remove qgis python-qgis qgis-plugin-grass

sudo apt-get autoremove

Now edit /etc/apt/sources.list by using the following command

sudo vi /etc/apt/sources.list

Note: Sudo is required because normal users do not have rights in /etc/apt/ folder.

Now this is where is trick is, instead of adding  debian or ubunutgis repositories add ubunutgis-nightly-release,  so add the following two lines in source. list

deb https://qgis.org/ubuntugis-nightly-release xenial main
deb-src https://qgis.org/ubuntugis-nightly-release xenial main

Rest is simple, first update

sudo apt-get update

and then install

sudo apt-get install qgis python-qgis qgis-plugin-grass saga

Thats it.

Some of the dependencies will not be there if we use ubuntugis-nightly-release repository reference.

Text Editors

In the last few years, I have tired many text editors like gedit, sublime, vi, vim and now Atom. You can read more about Atom on their website.

What I like about Atom is the packages, gedit and sublime also has packages (reference) for example I like cli panel in text editors, like Embedded Terminal in gedit

gedit

However, I needed a text editor that can support a cli and a webbrowser plugin (see the image below). Atom does that as it has a terminal-plus (don’t install it before you read the complete blog) and browser-plus.

Atom

Installation

Use the following commands on Ubunut to install Atom

sudo add-apt-repository ppa:webupd8team/atom

then

sudo apt update

sudo apt install atom

Packages

Some of the packages I like are (you can install them using atom builtin package manager or command line utility apm)

autocomplete-python 1.10.2
autocomplete-python-jedi
atom-bootstrap4 ver 1.4.0 

some other good autocomplete packages are

autocomplete-json

atom-django 0.3.2
django-templates

and some other packages

browser-plus 0.0.98
(open browser by using ctrl-alt-o)

emmet 2.4.3

linter-flake8 2.2.1

terminal-plus 0.14.5 (I had problems installing this one)

platformio-ide-terminal

Some Issue

Some installed packages could not be loaded because they contain native modules that were compiled for an earlier version of Atom like with terminal-plus package

Solution to terminal-plus package issue
https://github.com/jeremyramin/terminal-plus/issues/402

The solution worked on my unbunut 14 laptop, but I could not make it work on ubunut 16. I did some searching and then opted for “platformio-ide-terminal” as some one said it is not in development any more (the repo is at least one old https://github.com/jeremyramin/terminal-plus). The package “platformio-ide-terminal” works out of the box.

Note: For color change (in package setting), restart Atom after colors are changed.

if you want to remove atom, use the following command.

sudo apt remove --purge atom

What do you think, you want to give it a try.

Updates:

If you get an error like

Err:1 http://ppa.launchpad.net/webupd8team/atom/ubuntu xenial/main amd64 atom amd64 1.24.1-1~webupd8~0 
 Hash Sum mismatch

Do the following (reference)

sudo rm -rf /var/lib/apt/lists/*
sudo apt clean
sudo apt update

Excel functions

Microsoft Excel OR LibreOffice Calc are excellent tools for data cleaning. For small to moderate level tasks, I always use LibreOffice Calc but very time I use Calc functions, I have to search for functions as I cannot remember functions names or parameters. Thus this blog

Some interesting functions

1. Relplace/Remove unwanted characters

Ctrl+H is for find and replace, I use it all the time to remove special characters (end of line chearacter), spaces etc

2. Multiple data fields in one column.

Multiple fields in one column and I want them to be separated in multiple column

Example:
I have test “Alex 30years” in column A1 and as you can see these should be in two columns Name and age .I want any thing after first space to be in B1.

Now, will go to column B1 and paste the following

=MID( A1,FIND(" ",A1)+1,100)

Explanation:

  • FIND(“character”,cell_number) will find and return the location of given cheracter.

  • MID(cell_number) will extract substring from cell A1 and the substring will start from the location returned by FIND() function till 100th character (yes we can use lenth function instead of static number like 100)

3. sting concatenation

Have you seen a case where you have two or more columns and you want to generate a new column based on available columns. The colution is CONCATINATE() function. Here how it works

Example:
There are four columns with data

Alt

Now you want to column E to appear like “abc to z”. Click on cell/column D1 and use the following command

=CONCATENATE(A1,B1,C1," to ", D1)

I think its self explanatory :). This Example is not very interting so lets look at an interesting exmaple.

Suppose you have four pairs of latitudes/longitudes (a bounding box, see the image below) in columns and you want to make a csv which can be imported into qGIS in such a way that the columns becomes geometry.

Alt
We can generate a geometry column containing Well Known Text (WKT) by concatinating pairs of lat/long. Any GIS software that supports WKT will generate shapes based on this column.

Alt
and the code to generate wkt column is

=CONCATENATE("POLYGON ((",A2," ", B2,",",A2," ",C2,",",C2," ",D2,",",D2," ",B2,",",B2," ", A2,"))")

Save this exel sheet as csv and import in qGIS (by using layer – csv option). If every thing goes well, you will see a bolygon layer (like the one below)

Alt

Now if you have many rows, you can replicate the formula (by dragging it) on other columns.

Two interesting plugins for QGIS

QGIS has made its mark in FOSS4G and third party plugins make it more and more attractive. I will introduce two more plugins today which could also be useful  for you.

MultiQml

If you have many layers that require a similar style, you have to assign style for each layer one by one. Not any more, MultiQml can perform this tedious task for you.

First load all required layers. Second,  style any one layer and save the styling information as ‘QGIS Layer Style File’ below. You can use ‘Layer properties’ form to save styles (see below).

Screenshot from 2016-02-17 16:04:54

Start MultiQml from menu, perform the following

  1. Raster / Vector layer type
  2. Select all layers
  3. Apply style

Screenshot from 2016-02-17 16:09:32

The final operation will apply the same style (theme) to all the layers (in one go, saves a lot of time :)).

Table manager

In QGIS, if you want to change the attribute of shape file it is not possible directly. For example, you want to change the upper case character in field ‘Name’ to ‘name’, you cannot do that.

Now some one might think, why would I want to change the attributes from upper to lower characters. Well …. actually you don’t need to until you wan to upload this shape file to PostgreSQL/Postgis. If you have upper case character as attribute names (or as field names in database terms), you cannot access them (in a query) like normal attributes. For example a select on country shape file with upper character  (below) will return an error

select * from country where Name = ‘Sweden’;

one way to to correct the above query is to use quotes in field name

select * from country where “Name” = ‘Sweden’;

OR use ‘Table manager’ plugin to edit the attribute names. Start ‘Time Manager’ and it will pick the active layer and will show you all the attributes (below)

Screenshot from 2016-02-17 16:32:19

You can rename a attribute, change attribute order, clone an attribute, insert an attribute and delete an attribute.

puts, print and p in ruby

I’ve been trying to pick up Ruby and one of the things I was asking myself was the difference in the various ways you can output text.

  • puts: displays text and adds a newline character
  • print: displays text and doesn’t add a newline character (this means you must add newlines manually when using print)
  • p: while it’s similar to puts in that it adds a newline, it calls inspect instead of to_s This is why p can be more useful for debugging since it shows what class an object belongs to.

Screen Shot 2016-02-08 at 19.02.38

More references for those interested