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Sunday, May 15, 2011

QGIS for D&D part 2: picking up projection.

As it was discussed earlier, it could be wise to create a GIS-support for D&D campaign.  Let's describe it further. I suggest you read the manual for QGIS if you are not familiar with this software. And for information about projection, please read section 6 of QGIS manual (at present time manual for 1.6.0 version is available)

As we decided to use GIS, the first thing we have to take into account is projection(s) we will use. 

QGIS (as other GIS software) is a scientific programme and was not meant to be used for imaginary word, which parameters are obviously different to Earth. But I believe it is not a problem. Firstly, in QGIS it is possible to determine your own parameters for the ellipsoid of imaginary planet. PROJ4 is used in QGIS so you can read documentation if you want to do it the hard way.

To my mind it is Ok to use Earth parameters for your world - it will save a lot of time and our planet is actually big enough to place everything you need ;-) 

Here is my approach:
  1. It is necessary to define projection for the entire map - it should represent adequate squares of the empires, mounts, oceans, etc.
  2. It is necessary to define projection for the layers of the map - it should be easily utilised in any projection of the map.
  3. Projections for the map and layer are not necessary to be the same.

It is necessary to define projection for the whole project (section 2.5 of QGIS manual) and for the layers. Projection of the map should be equal area, because it will be handy to understand sizes of the Great Deserts and Dead Man's Lakes. To my mind Albers equal area conic projection is the best choice if only a part of the planet (world) is designed. You should decide where on the Earth globe your area is located ad define projection parameters accordingly. 

For example I use these parameters for current campaign: +proj=aea +lat_1=40 +lat_2=55 +lat_0=0 +lon_0=-120 +x_0=0 +y_0=-4000000 +ellps=WGS84 +datum=WGS84 +units=m +no_defs

You will need to adjust lat_1 and lat_2 parameters to frame latitudes for the desired location, and other parameters could be the same.

NB: units for the given example are meters, but it is obvious that DM would prefer foots for the length measurement. This is not a problem due to it is possible to set up needed units in project properties.

For layers it will be the best choice to use unprojected lat/long WGS84 reference system. It will allow its easy usage when you will decide to extend your world and evade a lot of re-projection issues.

The next issue to be encountered is starting drowning in the right place: the map will be totally empty and it will be hard to understand where the borders of the area should be located. But there is nothing to worry about: just decide where your area would be located at the Earth globe (lat/lon frame), then open the layer (lat/lon) in totally new project and use "Numerical Vertex Edit" tool (you will have to install ot via "Fetch Python Plugins" menu) to place several points with needed coordinates that will be an orienter for the area borders.

2 comments :

  1. I'm following this with great interest.

    I am a town planner and D&D fan who wants to learn GIS, so I thought creating a D&D map in GIS would be a fun way to practice.

    I thought I'd start by creating a GIS-based make of The Isle of Dread, from the classic game module. Is there a way to work in GIS with latitude and longitude?

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  2. >> Is there a way to work in GIS with latitude and >>longitude?

    Yeah, certainly, and WGS84 lat/lon is a default coordinate system in QGIS.

    If you will encounter any issue or need an advise, feel free to ask.

    P.S. if you use QGIS 1.7, then the collection of symbols located here might be useful.

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