View Full Version : Workflow suggestions regarding projections?
02-11-2013, 11:46 AM
I am currently working on some maps for a conworld project of mine, namely a world map and some close up shots of certain areas and I have been wondering how to deal with the different projections or how to choose one for the inital world layout.
I know there is G.projector which takes an equirectangular map to calculate other projections, however it only takes raster data and I am not quite sure how to fake the inital disortion of this projection, beside starting with a mercator projection and then 'squash' the top and bottom area using illustrator once vectorized ;)
Recently I also looked at GRASS/Quantum GIS but there seems to be no easy, bug free way to import/export svg, so I am not quite sure if I should try my luck with it or not.
Sooo... I guess I have been wondering how some of you handle this, or if it is handled at all. I could just hand wave it I guess, but it seems too inaccurate for my taste. Is there some sort of ideal workflow for deriving smaller maps from a world map? In any case I would be glad for any pointers you can give me :)
02-11-2013, 03:27 PM
I'd suggest if you want to work with GIS, that you start there rather than trying to import SVG into it. If you really want to import into it, your best bet is to use a raster image, georeference it, and then trace it.
The export functionality fron QGIS isn't that good at the moment, but if you keep your symbology clean and simple you can clean up the SVG or PDF output into something you can work with.
02-11-2013, 04:40 PM
Thanks :) I didn't consider about tracing it in GIS directly. I can't imagine I will get a complicate symbology so it should be alright. So I would start with something like mercator, import it, georeference and then trace it?
Is there anything else which can be added directly in the GIS beside vector and point data? I have only looked Quantum/Grass over so far so I am quite the noob ;) Would one add highmap data directly in GIS or are mountains something to do after the exporting? I am not looking for something complicated, just some lines indicating the height level the way it is done in an atlas.
02-11-2013, 05:03 PM
GISes do have the ability to work with raster data like DEMs ("Height fields") including some quite complex analysis, but they aren't designed for "painting" raster data from scratch. I remember seeing a contour plugin for QGIS that can computer contours from a raster surface, but you need that surface in the first place.
You might try this:
Select a regional projection. export, build up a DEM/height map in a graphics tool to match the exported map, georeference it, and load it back into the GIS. Now you can reproject it, compute contours, etc. You're really going to want a graphics editor and format that supports more range than an unsigned 8 bit integer per channel though. Real DEMs usually use floating point numbers, although 16bit integers could be made to work.
DEMs are really hard to make from scratch without looking horribly artificial.
You might find this useful: http://www.cartographersguild.com/tutorials-how/17469-%5Baward-winner%5D-some-pointers-using-gis.html
02-12-2013, 09:32 AM
Alright, that sounds doable. And yeah, I will need to look what other tools I can find. From work I am most used to work with illustrator/photoshop, but they were not really meant for this kind of task I figure ^^ For now I will concentrate on the continent contours.
I looked at your tutorial and found it quite useful. At first I reproduced the first steps using the vector data from natural earth, loading the file and then re-projecting it to some other projections as a test and it worked great. When I tried the same with a raster map however, I ran into some problems. I am not sure if QGIS is buggy though or if I made a mistake somewhere. While I could re-project the raster maps (down loaded some from NE) and the re-projection itself seems correct, it cuts of slices from the sides of the map. Projecting the original file to Mercator WGS 84 (EPSG:3395) for example cuts off a signignificant part of the top and bottom part of the map. I know mercator projections can't show the poles, however I am losing half of Norway too (everything north of Trondheim or so) which seems a little much. Other projections cut of the sides, so I am a little clueless what is going wrong.
The .tfw and .prj files are named the same name as the raster map and sit in the same folder too. Is there anything else I need to change to reproject raster maps? In photoshop I would suspect I am trying to draw beyond the canvas borders, but if QGIS has such a setting I was unable to find it so far.
02-15-2013, 01:53 AM
I just tried the same thing and it looks like a problem with On the Fly Reprojection. If you set the project CRS and enable On The Fly, all the layers will be projected into the project CRS Live, but this is computationally intensive, and not as reliable, particularly for Raster data. Try Raster -> Projections -> Warp. That will let you project the image to a new file.
02-17-2013, 05:13 AM
I do this:
Start the map with equirectangular, which you already know is used by G.Projector and other similar tools. It's a 2x1 map, and each degree x degree area is represented as a single square on the map. I do black and white outlines for the coasts, if I have poles, I do them separately by turning the map in Hugin, and then turning the map back and joining the edited bits into the main map (http://www.cartographersguild.com/tutorials-how/5158-removing-polar-distortion-using-hugin.html). (other Hugin tut (http://www.cartographersguild.com/tutorials-how/5025-hirez-map-projection-conversion-using-hugin.html))
I do the "data" in this phase: rivers, climates, roughly where mountains go etc. Then I transform these data layers with a projection converter into the target projection, and then I prettify the map. That's about it.
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