HI Ashim, & others, Coordinate systems, and their area of applicability is an abstruse topic, and one that has many complicated things to consider. So what I'm saying here is a user-friendly summary.
- The data in our Repository is in WGS-84 Lat/long, which has the EPSG code 4326. - You seem to be projecting it to ESPG: 2154, which is coordinate system applicable in France.( http://epsg.io/2154) I can't see a Valid reason for doing this. - If you need to project to a projected Coordinate System,(Maybe for calculating areas & distances) you should use EPSG:7755, ( http://epsg.io/7755) which is the one defined in NNRMS standards, and is used by many Government Organizations, like ISRO, NURM etc. - I generally* won't recommend* projecting to EPSG:3857, which is the webmercator projection, since it has several issues. *You should never measure areas or distances using this projection*. Regards, Devdatta On Tue, Apr 16, 2019 at 11:42 AM Nikhil VJ <nikhil...@gmail.com> wrote: > Hi Ashim, > > Pls provide the exact link of what you're referring - this stuff is never > as much on the top of people's minds as we assume it to be. > Do try loading your shapefiles on other tools and check there : > mapshaper.org is a site that does a lot of quick, cool things with > shapefiles; QGIS is a software that does everything with shapefiles. Both > are free and open source. > > The latter will help you re-save the shapefile into any CRS you want. > Right-click the layer > Save As (or "Export") and remember to choose your > preferred CRS in the dropdown. > > Can you give background on what this CRS : *2154* : is and why you want > to transform to that? Because I've only come across two main CRS's both > being under the "WSG 84" category : > - EPSG 4326 : this makes everything in latitude longitude > - EPSG 3857 : this makes everything in meters from the equator (I think) > and we need to get the data in this format when we want to do things in > physical distance terms like making a 1km distance buffer or measuring areas > > I haven't learned GIS stuff from theory, I just use it, so don't know more > details about CRS. I do understand that the dizzying multitude of CRS's out > there are so because apparently GIS folks like to re-orient the center of > the world (geometrically speaking) to where their data is to ensure least > distortion of their shapes in the rendering. When I come across anything > that's in a non-standard CRS, my first move is to transform it to either > lat-longs (4326) or meters (3857). > > Regards > Nikhil VJ > > > On Monday, April 15, 2019 at 1:57:20 PM UTC+5:30, Ashim wrote: >> >> Dear All, >> >> I am referring to 2011_Dist. * set of shapefile. (District level >> shapefiles). >> >> When I read them as simple features in R, ( like this ) >> >> map <- st_read("2011_Dist.shp") %>% st_as_sf() >> >> ( it's unprojected because it says 4326 in the epsg when I read the above >> ) >> >> plot(map$geometry) >> >> it looks OK. >> >> But when I do : >> >> map <- st_read("2011_Dist.shp") %>% st_as_sf() %>% st_transform(crs= 2154) >> >> plot(map$geometry) >> >> the map is TILTED. >> >> What is the correct projection to use for this dataset? Please clarify. >> >> Best Regards, >> Ashim >> > -- > Datameet is a community of Data Science enthusiasts in India. Know more > about us by visiting http://datameet.org > --- > You received this message because you are subscribed to the Google Groups > "datameet" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to datameet+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- Datameet is a community of Data Science enthusiasts in India. Know more about us by visiting http://datameet.org --- You received this message because you are subscribed to the Google Groups "datameet" group. To unsubscribe from this group and stop receiving emails from it, send an email to datameet+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
