“There exist no all-purpose projections, all involve distortion when far from the center of the specified frame” ( R. The question of which CRS is tricky, and there is rarely a ‘right’ answer: In some cases transformation to a projected CRS is essential, such as when using geometric functions such as st_buffer(), as Figure 6.1 showed.Ĭonversely, publishing data online with the leaflet package may require a geographic CRS.Īnother case is when two objects with different CRSs must be compared or combined, as shown when we try to find the distance between two objects with different CRSs: However, there are some general principles provided in this section that can help you decide.įirst it’s worth considering when to transform. There are no clear-cut answers to these questions and CRS selection always involves trade-offs ( Maling 1992). The main task involving CRSs is often to transform objects, from one CRS into another.īut when should data be transformed? And into which CRS? In real world applications, however, CRSs are usually set automatically when data is read-in.
Github reprojecting to mapublisher how to#
The previous section showed how to set the CRS manually, with st_set_crs(london, 4326). This suggestion does not always need to be heeded: performing spatial and geometric operations makes little or no difference in some cases (e.g., spatial subsetting).īut for operations involving distances such as buffering, the only way to ensure a good result is to create a projected copy of the data and run the operation on that. It is better understood as a suggestion to reproject the data onto a projected CRS. Lines of latitude, by contrast, are equidistant from each other irrespective of latitude: they are always around 111 km apart, including at the equator and near the poles (see Figures 6.1 to 6.3).ĭo not interpret the warning about the geographic ( longitude/latitude) CRS as “the CRS should not be set”: it almost always should be!
Github reprojecting to mapublisher code#
The distance between two lines of longitude, called meridians, is around 111 km at the equator (execute geosphere::distGeo(c(0, 0), c(1, 0)) to find the precise distance).Īt the latitude of London, for example, meridians are less than 70 km apart (challenge: execute code that verifies this).
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