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Map corner coordinates in QGIS

Some time ago in the qgis-pt mailing list, someone asked how to show the coordinates of a map corners using QGIS. Since this features wasn’t available (yet), I have tried to reach a automatic solution, but without success, After some thought about it and after reading a blog post by Nathan Woodrow, it came to me that the solution could be creating a user defined function for the expression builder to be used in labels in the map.

Tuesday, September 9, 2014 | 5 minutes Read

Please use the "IN" operador

It’s not the first time I see people that, to select feature by their fields values, use expressions like this: [code language=“SQL”]“field” = ‘value1’ OR “field” = ‘value2’ OR “field” = ‘value3’ [OR …][/code] A more practical and pretty way of doing this is by using the IN operator instead. [code language=“SQL”]“field” IN (‘value1’,‘value2’,‘value3’[,…])[/code] This operator is available in almost every GIS software I know. In QGIS, it can be used even if there isn’t a small little button to click.

Tuesday, June 24, 2014 | 1 minute Read

Old map in QGIS

Inspired in a post by Anita Graser, I’ve tried to use QGIS to create a Cascais’s old looking map, as if it have been drawn by hand in a methodical way. Defining the styles I have started by defining the styles for each elements to represent. Buildings To fill the buildings, I have tried to use a color that reminds me the portuguese roofs, similar to the color commonly used in old maps of cities, with a slightly darker outline of the same color.

QGIS

Monday, April 14, 2014 | 2 minutes Read

Multipart Split

This QGIS plugin Multipart Split allows the user to, during edition, split the active layer’s selected multipart features into single part features. Unlike the “Multipart to single part” from the Vector > Geometry Tools menu, the plugin only splits the selected elements, and does not need to create new files. Installation The plugin is available in the QGIS official repository, therefore the installation is done in the Manage and Install Plugins (Plugins > Manage and Install plugins…).

Tuesday, March 25, 2014 | 1 minute Read

New QGIS plugin - "Walking time"

I have finally “finished” my new plugin. I uses some quotation marks, since I believe that there is still space for a few improvement. This plugin arised with the need to calculate the travel time for the Cascais oficial pedestrian routes, and started as a simple python script. I have then decided to create a graphic interface and publish it as a plugin in the hope that someone else finds it useful.

Tuesday, March 25, 2014 | 1 minute Read

Walking time

The Walking time is a QGIS python plugin that uses Tobbler’s hiking function to estimate the travel time along a line depending on the slope. The input data required are a vector layer with lines and a raster layer with elevation values (1). One can adjust the base velocity (on flat terrain) according to the type of walking or walker. By default, the value used is 5 km h (2). The plugin update or create fields with estimated time in minutes in forward and in reverse direction (3).

Tuesday, March 25, 2014 | 1 minute Read

Substituir strings na tabela de atributos do QGIS

Hoje, ao rever uma camada vectorial de distribuição de fauna com interesse para a conservação com a nossa bióloga de serviço, Sara Saraiva, tive necessidade de corrigir (em todas as linhas de determinado atributo) o nome “Aquila fasciatus”, substituindo-o por “Aquila fasciata”. Devido à opção tomada na organização dos dados, cada polígono continha uma listagem de espécies que nele ocorrem, e o nome a corrigir encontrava-se no meio da mesma. A correcção teria de ser feita sem alterar os restantes nomes.

QGIS

Wednesday, May 29, 2013 | 1 minute Read

Visualizar dados dos Censos 2011 com o QGIS

Felizmente parece que algumas coisas vão mudando no nosso país no que toca ao acesso a dados. A Base Geográfica de Referenciação da Informação (BGRI), que outrora foi paga (e bem paga), está agora disponível a todos até ao nível da subsecção estatística e com um total de 122 variáveis dos censos 2011 (organizados por população residente, população presente, famílias, alojamento e edifícios). A página para download, permite descarregar os dados totais para Portugal, ou por regiões e concelhos.

Tuesday, May 7, 2013 | 3 minutes Read

Definir a representação de pixeis sem valor em mosaicos de imagens VRT

Como está muito bem descrito neste artigo do Duarte Carreira, a criação de catálogos virtuais (vrt) e respectivas pirâmides (overviews) usando o GDAL, permite facilitar e melhorar a performance de visualização de mosaicos de imagens. Usando o comando gdalbuildvrt para criar o catálogo virtual, as áreas sem valor (NoData) são, por defeito, substituídas pelo valor 0. Em certos caso, o efeito pode não ser o mais desejável. gdalbuildvrt mosaico1.vrt --optfile listadeimagens.

Wednesday, April 24, 2013 | 1 minute Read

Open Source, why?

During my professional and personal life, I have worked with much different software, with all kinds of licenses. Most of them would be proprietary, closed and / or commercial code. So why devote my time and learning “exclusively” to Open Source? Without going into detail about the differences between open source software and free software, there are several reasons why FOSS (Free and Open Source Software) interest me. The first is obviously freedom.

Sunday, March 31, 2013 | 2 minutes Read

Welcome note

The blog “GIS Unchained” have borne devoid of any grandiose aspirations. The main objective will be to register my experiences with Open Source software while addressing challenges related to geographic information systems (GIS), spatial analysis, cartography and everything else that it might entail. Following the same principle of openness and sharing of the open source, I hope that these records can help others who, like me, “venture” into this world.

Tuesday, March 26, 2013 | 1 minute Read