Hi Devdatta Thanks a ton for the correction! I'll use EPSG:7755 for distance related work here on out.
-- Cheers, Nikhil VJ, Pune, India http://nikhilvj.co.in On Tue, Apr 16, 2019 at 11:56 AM Devdatta Tengshe <[email protected]> wrote: > 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 <[email protected]> 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 [email protected]. >> 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 [email protected]. > 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
