I am trying to put a SHP file into my PostGIS database, the the data is just a little off. I think this is because I am using the wrong SRID. The contents of the PRJ file are as follows:
GEOGCS["GCS_North_American_1983",
DATUM["D_North_American_1983",
SPHEROID["GRS_1980",6378137.0,298.257222101]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]]
What SRID does this correlate to? And more generally, how can I look up the SRID based on the information found in the PRJ file? Is there a lookup table somewhere that lists all SRID's and their 'geogcs' equivalents?
The data imported using srid=4269 and 4326 were the exact same results.
Does this mean I'm using the wrong SRID, or is this just expected margin of error?
The shp file is from here.
To elaborate on synecdoche's answer, the SRID is sometimes called an "EPSG" code. The SRID/EPSG code is a defacto short-hand for the Well-Known-Text representations of projections.
You can do a quick search on the SRID table to see if you can find an exact or similar match:
SELECT srid, srtext, proj4text FROM spatial_ref_sys WHERE srtext ILIKE '%BLAH%'
Above was found at http://www.bostongis.com/?content_name=postgis_tut01.
You can also search on spatialreference.org for these kinds of things. The search tool is primitive so you may have to use a Google search and specify the site, but any results will show you the ESRI PRJ contents, the PostGIS SQL INSERT, and a bunch of other representations.
I think your PRJ is at: http://spatialreference.org/ref/sr-org/15/
Prj2EPSG is a small website aimed at exactly this problem; paste in the PRJ contents and it does its best to find a matching EPSG. They also have a web service API. It's not an exact science. They seem to use Lucene and the EPSG database to do text searches for matches.
The data seems to be NAD83, which has an SRID of 4269. Your PostGIS database has a spatial_ref_sys table which is the SRID lookup table.
If the data looks the same with an SRID of 4269 (NAD83) and 4326 (WGS84), then there's something wrong.
Go and download the GDAL utilities , the ogrinfo (which would spit the projection information) and ogr2ogr utilities are invaluable.
James gave already a link to spatialreference.org. That helps to find spatial reference information... I assume you did load the spatial_ref_sys.sql when you prepared your postgis instance.
And to be honest, I don't think the problem is in the PostGIS side of things.
I usually keep my data in different SRIDs in my PostGIS dbs. However, I always need to project to the output SRS. You are showing OpenStreetMap pre-rendered tiles, and I bet they have been drawn using SRID 900913 (the Google Map's modified mercator projection that now everyone uses to render).
My recommendation to you is:
1- Set the right projection in the OpenLayers code which matches whatever tiles you are reading from.
2.- Keep the data in the database in whatever SRID you want (as long as it is correct of course).
3.- Make sure the server you are using to generate the images from your data (ArcGIS Server, Mapserver, GeoServer or whatever it is) is reprojecting to that same SRS.
Everything will match.
Cheers
Use GDAL's OSR Python module to determine the code:
from osgeo import osr
srsWkt = '''GEOGCS["GCS_North_American_1983",
DATUM["D_North_American_1983",
SPHEROID["GRS_1980",6378137.0,298.257222101]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]]'''
# Load in the projection WKT
sr = osr.SpatialReference(srsWkt)
# Try to determine the EPSG/SRID code
res = sr.AutoIdentifyEPSG()
if res == 0: # success
print('SRID=' + sr.GetAuthorityCode(None))
# SRID=4269
else:
print('Could not determine SRID')
Be sure to take a look at: http://www.epsg-registry.org/
Use the Query by Filter option and enter: North American Datum 1983.
This yields -> EPSG:6269.
Hope this works for you.
Related
so I have a lot of GPXs of users driving data from a game project where object which are placed on the road and then the user collects it. I want to somehow analyze these data to find out how users tend to drive given different objects, which ones draw them the most, which ones draw least. I have not done any data analysis before, so how can I analyze these data to get this sort of information? This might sound very novice, but yeah any help is appreciated.
You would probably like to do this in Python if you are novice, and then you can use a library like this one (gpxpy) to explore your data.
That is a GPX parser, I believe it will provide you with the data you like to see.
In their documentation you can see that you can use it like that :
import gpxpy
import gpxpy.gpx
# Open a file
gpx_file = open('yourfile.gpx', 'r')
# Parse the file
gpx = gpxpy.parse(gpx_file)
# Iterate over the tracks
for track in gpx.tracks:
for segment in track.segments:
for pt in segment.points:
print(f'Point at ({pt.latitude},{pt.longitude}) -> {pt.elevation}')
for waypoint in gpx.waypoints:
print(f'waypoint {waypoint.name} -> ({waypoint.latitude},{waypoint.longitude})')
for route in gpx.routes:
print('Route:')
for pt in route.points:
print(f'Point at ({pt.latitude},{pt.longitude}) -> {pt.elevation}')
Once you have those points you can calculate the distances, speeds, etc. from the coordinates.
I am currently converting a shapefile into a GML file for an online Mapviewer. this application requires the geometry to be in a seperate attribute and needs to consist of multicurve features.
using GeometryExtractor, i get the following:
<rrgs:geometrie>
<gml:LineString gml:id="id-9f7691bb-868d-457e-9061-aceb37980a59-0" srsName="EPSG:28992" srsDimension="2">
<gml:posList>260471.21250000037 591380.1363999993 260457.43054999973 591385.7507499998</gml:posList>
</gml:LineString>
</rrgs:geometrie>
however, the application for uploading onto the online mapviewer requires the geometry as follows:
<rrgs:geometrie>
<gml:MultiCurve gml:id="…" srsName="EPSG:28992" srsDimension="2">
<gml:curveMember>
<gml:LineString gml:id="id-9f7691bb-868d-457e-9061-aceb37980a59-0">
<gml:posList>260471.21250000037 591380.1363999993 260457.43054999973 591385.7507499998</gml:posList>
</gml:LineString>
</gml:curveMember>
</gml:MultiCurve>
</rrgs:geometrie>
would it be possible in FME to convert linestring features into multicurve features?
Thanks in advance!
I would try just setting an Aggregator before writing so all geometries are multi-geometries.
You would need to use an attribute with a unique value in the Group By parameter so the different features aren't grouped together. If there's none try the UUIDGenerator.
I'm working on google map search functionality. The vision of this is to find whether a (geolocation) point is located within a polygon or not as shown in the illustration below?
I'm using mysql 5.6.20 with Spatial extension, I know it has useful geometry functions built-in, so I will be allowed to query geocoded locations from a database directly.
My aim was to familiarize myself with geospatial functions, so I wrote up an experimental sql.
given a point geolocation: POINT(100.52438735961914 13.748889613522605)
and a polygon or boundary to be tested with was:
POLYGON(100.49503326416016 13.766897133254545,100.55940628051758 13.746555203977,100.56266784667969 13.72170897580617,100.48885345458984 13.739051587150175)
here is my sql example:
SELECT ST_Within(
ST_GEOMFROMTEXT('POINT(100.52438735961914 13.748889613522605)'),
ST_GEOMFROMTEXT('POLYGON(100.49503326416016 13.766897133254545,
100.55940628051758 13.746555203977,100.56266784667969 13.72170897580617,
100.48885345458984 13.739051587150175)'))
As geoFenceStatus
but after issuing the command, what I got in return seemed to be as follows:
geoFenceStatus
===============
null
I'm so unsure why it returned me 'null' value. since it was indicated in function documentation that this should return '1' in case a point resides within a given polygon
any advice would be appreciated, how to get my sql right.
The error message isn't very clear but your issue is that you have an invalid Polygon. There are two problems with it:
You have to repeat the first point at the end -- this is to differentiate it from a LINESTRING, essentially, ie, it is closed.
POLYGONS start with and end with double parenthesis, ie, POLYGON((x1 y1, x2 y2.......xn yn, x1 y1)). This is to allow for inner rings to be delineated with single parenthesis sets inside the polygon.
See the wikipedia WKT article for more information.
You should find that if you write you query as:
SELECT ST_Within(ST_GEOMFROMTEXT('POINT(100.52438735961914 13.748889613522605)'),
ST_GEOMFROMTEXT('POLYGON((100.49503326416016 13.766897133254545, 100.55940628051758 13.746555203977,100.56266784667969 13.72170897580617, 100.48885345458984 13.739051587150175,
100.49503326416016 13.766897133254545))'))
As geoFenceStatus
then is should work.
i need to find out what is the best method for what i'm looking.
Basically, based on user position (lat and lng coords.), i need to find their corresponding city..
my first attempt was gmaps (reverse geocoding):
Pros:
easy to use
Cons:
use is limited to N requests
according to their policies, using reverse geocoding without any visual in frontend is prohibited.
Each country has their own typography ( there is no standart field to obtain):
my second scenario, was mysql geospational:
After download gadm shape files, i tried to convert them para mysql using shp2mysql but no success..
Pros:
there is no need any external service to retrieve city
My Cons:
Unable to use them correctly.
So, am i on a right way? is second approach better than one? i only need cities/countries based on a user location, nothing more..
Any sugestion or maybe a good tutorial?
After hours:
CREATE TABLE geom (g GEOMETRY NOT NULL, SPATIAL INDEX(g)) ENGINE=MyISAM;
Next:
C:\Program Files\FWTools2.4.7>ogr2ogr -f MySQL MySQL:dbname,user=root
,password=root C:\shape_pt\PRT_adm1.shp -nln geom -update -overwrite -lco GEOMET
RY_NAME=g
ERROR 1: MySQL error message:The used table type doesn't support SPATIAL indexes
Description: ALTER TABLE `geom` ADD SPATIAL INDEX(`g`)
ERROR 1: Terminating translation prematurely after failed
translation of layer PRT_adm1 (use -skipfailures to skip errors)
Any suggestion?
I see that the following syntax is used in examples:
GeomFromText('Polygon((1 1, 2 2, 3 3))');
The double parenthesis caused a bit of a trouble so I decided to look it up in the official documentation. At my non-small surprise the search mysql polygon did not give me the documentation of this function. A search to mysql geomfromtext also did not give the definition of the function GeomFromText.
So I'm still looking for the official documentation of these functions.
I see that the MySQL Reference Manual for GeomFromText() doesn't even give a typical function definition either, but it does describe how to use it. GeomFromText() converts from "well-known text" (abbreviated as WKT) to MySQL's internal format. WKT is simply a textual representation of a geometry object, which can be a polygon as your example, or any of the other geometry types. A key point to understand is that Polygon(...) is the WKT format for a polygon; it isn't a MySQL function call, even though it sort of looks like one.
Polygons can contain holes. When defining a polygon, you may optionally supply one or more interior boundaries to define such holes. The WKT for polygons use inner parentheses to distinguish these boundaries from one other. Even if you don't want to define holes, the inner parentheses are still required. Wikipedia provides some simple examples of polygon WKTs together with pictures of the resulting polygons.