Thanks for the detailed info! On Thu, Aug 1, 2019 at 10:21 PM Calle Hedberg <calle.hedb...@gmail.com> wrote:
> Dave, > > EPSG is a structured data set of Coordinate Reference Systems and > Coordinate Transformations - the data set was originally designed by the > European Petroleum Survey Group (EPSG) but is from 2005 maintained by the > International Oil and Gas Association Survey Committee. > > Each EPSG has a unique Spatial Reference Identifier (SRID), and as > indicated above it defines both the DATUM (Coordinate Frame, or in more > daily English it's a model of the Earth), the PROJECTION (or no > projection), and the necessary parameters for transforming data from one > EPSG to another. > > The EPSG = 4326 which Avin references above is the most basic/common EPSG > of all: the datum is WGS-84 (defined by the US and used in their GPS > system), and it uses decimal degrees with no projection: north-south > LATITUDES go from 0 degrees at the equator to 90 degrees at the North Pole > and -90 degrees at the South Pole, and east-west LONGITUDES go from the 0 > degree meridian (historically called the "Greenwich Meridian") to 180 > degrees eastwards and -180 degrees westwards. > > US datums and projections (like UTM, Universal Transverse Mercator) became > dominant for global cartography after World War 2 due to the US economic > and military dominance, which continued with their World Geodetic System > 1984 datum (WGS-84) used for their GPS Global Navigation Satellite System > (GNSS) - but that dominance is slowly fading and there are more global > players in the GNSS arena: > - the Russian GLONASS GNSS uses the PZ-90 datum > - the European GALILEO GNSS uses the GTRF datum > - the Chinese BIDOU GNSS uses the CGCS2000 datum > Before these recent global datums we had several hundred local datums, > based on land surveying by either military or civilian surveys (guys > trekking from hilltop to hilltop using theodolites and the like). > > The global datums above is always to some extent a compromise, trying to > average out errors for the whole globe. Which is why countries are still > creating variants of these because they want/need higher accuracy for > things like cadastral mapping (land parcel ownership boundaries), where you > usually require 5cm or better accuracy in urban areas to avoid too many > lawyer feasts when neighbours start feuding over the fence. South Africa, > for instance, have their own "Hartebeeshoek" datum that differs from WGS-84 > by 20-30 centimetres only... (Geographers are funny creatures - the > adrenaline rush the rest of us get from e.g. kinky sex, they get from > improving geodetic accuracy by 7 millimetres...) > > Now add a large number of potential projections - where the round earth > surface is projected onto a flat surface - and you see why POSTGIS have > over 5,000 EPSGs in its spatial reference system table. > > For normal users of navigational data (smart-phones etc), it's usually > relatively simple: Modern GNSS chipsets are increasingly seamlessly > handling and combining the signals from all satellites (31 GPS, 24 GLONASS, > 27 GALILEO, 27 BEIDOU), and they convert it into whatever EPSG/SRID the > user prefer or whatever is used by their apps. > > This was probably more than you wanted to know about EPSG, but you can > always dump it again when your grey cell ram gets full ;-) > > Best regards > Calle > > > > > > On Thu, 1 Aug 2019 at 12:45, Avin Kavish <avinkav...@gmail.com> wrote: > >> Hey bobb, >> >> but we have a custom EPSG, where do I add this into PGAdmin4 >>> >> >> EPSGs are stored in a table called spatial_ref_sys. All you need to do is >> insert a record that contains the definition in well known text format and >> proj4 format (for transformation). I'd recommend checking the table first >> because there over 5000 EPSGs in it. epsg.io shoud give you an idea of >> what the insert statement should look like. Example >> >> INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) >> values ( 4326, 'EPSG', 4326, '+proj=longlat +datum=WGS84 +no_defs ', >> 'GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS >> 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]]') >> >> >> Also, it would be nice to add in our own background mapping layers as >>> well, is there a method for adding in WMS/WFS to the layer list? >> >> >> Till support for custom layers land, once you have added your custom EPSG >> to the database you can transform the geometries to SRID 4326 and assuming >> they are on Earth, they will show up on the map. The following functions >> will be helpful >> >> st_srid - Check the SRID of a shape >> st_setsrid - Change an SRID without transforming coordinates >> st_transform - Transforms a geometry from one EPSG to another >> >> So when you are selecting data from a different EPSG, use: select >> st_transform(geometry, 4326) from table_name and it will enable the world >> map. AFAIK no other EPSG is supported for viewing on the map without >> transformation. I discovered it by sheer accident. >> >> >> >> On Wed, Jul 31, 2019 at 7:54 PM Basques, Bob (CI-StPaul) < >> bob.basq...@ci.stpaul.mn.us> wrote: >> >>> All, >>> >>> Following the appreciation thread and saw the reference to the geometry >>> viewer, I didn’t even know that was in there. Anyway, nice, but we have a >>> custom EPSG, where do I add this into PGAdmin4? >>> >>> Also, it would be nice to add in our own background mapping layers as >>> well, is there a method for adding in WMS/WFS to the layer list? >>> >>> Thanks >>> >>> bobb >>> >>> >>> >>> > > -- > > *Carl-Anders (Calle) Hedberg* > > HISP > > Researcher & Technical Specialist > > Health Information Systems Programme – South Africa > > Cell: +47 41461011 (Norway) > > Iridium SatPhone: +8816-315-19119 (usually OFF) > > E-mail1: ca...@hisp.org > > E-mail2: calle.hedb...@gmail.com > > Skype: calle_hedberg > -- Dave Page Blog: http://pgsnake.blogspot.com Twitter: @pgsnake EnterpriseDB UK: http://www.enterprisedb.com The Enterprise PostgreSQL Company
