I wish to display a map in QGIS (world country shapefiles) showing all countries but centered on the Pacific area. I am not familiar with Proj4, so is there any way this can be done in QGIS please?
Well, not that easy, as QGIS does not come with predefined Robinson or Miller projections.
So I tried a Custom CRS and got this picture (not in first run!):
For a central meridian at 150° West, it is necessary to split the world boundaries shapefile at 30° East (to be precise, at 29.9 and 30.1 to avoid intersections)
So these are the steps:
For the Miller projection, you can use the same pre-cut shapefile. In Proj, Miller has some problems with the ellipsoid, so we take a sphere instead (you won't see a difference):
With on-the fly activated, it does not look as well, New Zealand is missing at full extent, but returns when zooming in. So we need to
QGIS comes ready supplied with everything you need (i.e. it handles Proj4 for you under the hood). If your data are already in the projection you want, then right-click the layer and choose "Set Project CRS from Layer". This will put the data view into the same projection as your data. You will probably have to also right-click your layer and choose "Zoom to Layer Extent".
If your data are in some other projection, you can either reproject on the fly (in project properties) or reproject the data itself by right-clicking your layer and choosing "Save as". When the save dialog box opens, select the CRS for the output dataset and then use the new reprojected dataset.