How to display both scalebar in kilometres and lat/long degrees and northings/eastings in QGIS 1.8 Composer?
Layer is projected to UTM.
How to display both scalebar in kilometers and grid in lat/long degrees in Quantum GIS 1.8 Composer?
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2 Answers
Lat/lon 'grids' are usually called 'graticules'. I think the method for creating a lat/lon graticule as described in this document is sound. However, I think that the resulting shapefile needs further processing to make it plot properly on a projected map (UTM for example) such as yours.
After creating the graticule the lines should be densified to add extra vertices to them: Vector -> Geometry Tools -> Densify geometries. I used a value of 100 to produce the graticule shown as blue broken lines in the picture. The extra vertices in the lines 'pegs them to the ground' at more frequent intervals. Before densifying each line was defined by just two vertices, one at each end, and would plot as a straight line on a projected map, which it shouldn't. You can see the errors that arose with the graticule shown on the map in the document. Apparent errors I should say, I'm open to correction if I'm wrong about this.
Nick.
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@ nhopton You are right, your solution provides a better representation of the graticule. Commented Aug 29, 2012 at 1:24
In essence QGis uses the CRS of your project for both the scale bar and the grid.
To show a secondary grid look at this link
http://www.surfaces.co.il/?p=616
for the scale bar I do not know...
Hope it helps
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Greetings Gerardo, are you entirely happy with the lat/lon graticule in the document to which you linked? It doesn't look right to me, shouldn't the parallels be curved? N.– nhoptonCommented Aug 28, 2012 at 18:32
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Saludos Nick! I am sure you are right, one thing data seems to be near the Ecuator and relatively near the Greenwich, so they must not show to much curvature... Commented Aug 28, 2012 at 18:45
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@nhopton I was playing with a grid generated with vector/researchtools/vector grid and another one generated with mmqgis. I also made the procedure to densify the grid on both. The ones I made in mmqgis (densified and not densified) do not show any displacement when living in another crs..The one with created with f tools does show the displacement. That may be a good solution, instead creating the grid with ftools, create it with mmqgis, What do you think? Commented Aug 29, 2012 at 13:38
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@nhopton I extended the experiment and added a text point layer, reprojected to INEGI ccl. the point layer has points at the same intervals as the grids. Grids created with mmqgis do intersect with the points, the ones created with ftools do not, let me know what you think.. Commented Aug 29, 2012 at 13:54
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For me, line grids and graticules created with ftools and then densified works very well. The lines have ordinate data too, which is handy for labelling. I use this method for putting GB Ordnance Survey grids on OpenLayers. Don't have an explanation for the difference between grids made with mmqgis and those made by ftools I'm afraid. N.– nhoptonCommented Aug 29, 2012 at 14:50