• UsingProjections

This Howto applies to Qgis version 0.7 or higher. It's meant to help explain how to use what's probably the biggest new feature in 0.7, the ability to dynamically reproject vectors. This is illustrated as a worked example, taken from the perspective of the recreational GPS user. Hopefully hardened GIS wizards will get something out of it as well.

Our desired final output is something like this

What do we need?

• Some vector data. (In this example I'll be using GpxFiles)

• A GeoReferencedBaseMap

How do we get there? Let's build it up.

NOTE: for licensing reasons, I can't give out the raster I'm using in this demo. Sorry about that. I'd like to try and redo this example with a freely available raster, but I don't have any gpx files that cover a freely available area, sorry

So, fire up qgis. Click "Layer"->"Add Raster", and choose your GeoReferencedBaseMap. You should see something like

Next, click "Settings"->"Project Properties" and click on the Projections tab. Here, you choose the projection that represents your GeoReferencedBaseMap. In my case, I also assigned a projection to my raster, so the projection dialog is already showing the projection system I plan on using.

You always want to choose the projection that your raster is defined in. We don't support reprojecting rasters on the fly, so if you choose something other than the projection of the raster, then your images won't line up. If you need help getting your raster set up, then have a look at GeoReferencedBaseMap again.

So, you're looking at a window that looks something like

Make sure you put a tick in "Enable on the fly projection" ¹

Nothing should change in the display, but now we're set up to start laying down some layers. Click Plugins->Gps->Gps Tools. (Or click the gps icon in the toolbar) (If you don't have the gps plugin loaded, go via the plugin manager in the same menu and enable it) If you have some other sort of vector layer, like an ESRI Shapefile, you can just use Layers->Add vector layer. (And then skip the next three slides) If your gps data is in some format other than gpx, then you need to use GpsBabel to convert it.

You should see

Click the "..." button, and choose a file...

Should now be at something like

Press Ok, and Vóila! You should now have three new layers, one for each of tracks, routes and waypoints, and your tracks, routes and waypoints should all be lined up on the map where you expect them too. Something like

(No waypoints or routes in my file, so just the thin pink line)

Well, that's great, but that pink line is a yucky colour and it's a bit thin. ² So let's change it! Right click the track layer, and choose properties

Just change Outline colour and width to something more useful. Press ok, and presto, now we've got a pretty map like

Note that the legend changes with us, so we can always tell what's what when have multiple layers loaded up.

Here's an example of a more interesting source file.

In this one, I've gone into the layer properties and made the symbol for a waypoint bigger and more obnoxious so you can see it a bit easier. It's a bit boring though, so let's display the waypoint names we carefully added out in the field, or by using Qgis to add the points Right click the waypoints layer and choose properties, and the "Labels" tab. Should look like

• Click Display Labels, and choose the field you want to display (normally name) from the drop down. Choose a big obnoxious font and colour like I did, and choose where you want to display it. All reasonably self explanatory. Experiment a bit! ³

Here we are again,

My labels now showup, and to make it a bit easier to read, I right clicked my raster layer, and adjusted the transparency a bit.

The only thing left to do is "file"->"export as image" and you're done!

Hope this all helped a bit. And if things are unclear, use the wiki power to clarify it