I have the need to store 3D objects in a user defined space but I am having difficulty with the idea of creating a user defined world with PostGIS. Can I create a virtual world using PostGIS to leverage all of the spatial math functions and indexes without having to place my "world" on the surface of the earth? I would be ok with this world existing at the center of the earth if I had to.
Goals:
Store rectangular prisms in a user defined 3D space/coordinate system.
Have sub-coordinate systems within another coordinate system
Calculate intersections of said rectangular prisms and other spatial calculations.
Load information from a CAD drawing into a database
Is this possible with PostGIS? There is so much information out there that it is hard to consume so I would appreciate any type of answer suggesting do-able but difficult, easily do-able, or go a completely different direction than PostGIS. Thanks in advance.
Related
I store GPS tracks in Postgres with PostGIS and would like to find intersections between them not just in space but also in time. I'm thinking of using 3D geometry but treat 3rd coordinate as time. Basically as soon as new data comes I insert POINT(lat, lon, t) into a GPS track. To find intersections I make a query to find nearby objects along the path (a LINESTRING).
Based on what I know about PostGIS and spatial indexes it should work just fine. From the other side this kind of unorthodox usage of a spatial coordinate makes me a bit nervous. Is it ok to use PostGIS this way or there are better way to do what I want?
I´ve got a job offer to work with postgres and I have not much idea of it. The guy told me to build a simple data base which automatically calculates the distance to my house from a list of some other places (bars, pharmacies, museums, whatever...) everything given in geocoordinates.
I have already installed postgres, also postgis and create a data base. May you give me some hints about how I should do this task? Is there any tutorial or resource I could use to make this tasks easier? Should I use postgis?
Thank you.
PostGIS will do this easily. Boundless Geo have an excellent PostGIS tutorial. I also recommend you are familiar with Ch3 & 4 of the PostGIS manual.
I strongly advise you to learn & understand the difference between projected and unprojected coordinates if you're going to be working with spatial data. Projected means the coordinates have been taken from a 'round earth' and adjusted or projected onto to a flat map page (with coordinates normally given in feet or metres depending on the properties of the projection used). This enables computationally efficient normal cartesian calculations to be done for distance, area, direction, intersection, contains etc. There are trade offs for using projections- You can't preserve all of area, distance, shape, direction when you project a curved line or surface onto a flat map. Different projections are optimised for different trade-offs. Calculations on projected data are only accurate over a relatively small portion of the earth's surface. There are many map projections available to suit various needs and localities. If you are going to be working with projected data, you need to pick a projection that suits your purposes and location. If you don't understand projections, your queries can easily produce garbage without realising it.
Unprojected data (ie, raw Lat/Lon coordinates which is what you have) involve much more complicated calculations as they are done on the curved surface of the spheroid representing the earth. There are a number of reference coordinate systems that are used to express Lat/Lon, however the most common is "WGS84" (which is what "GPS" coordinates are expressed in).
PostGIS objects (in the form of "simple features" as defined by the OGC) can be stored as either "geometry" types (projected coordinates) or "geography" types (unprojected Lon/Lat in WGS84: note the order, a common source of confusion!). As a bit of a wrinkle, Lon/Lat (order again!) can also be stored as a "pseudo projected" geometry type (typically with a projection SRID of '4326' for WGS84 Lon/Lat).
The method you use to calculate distance will depend on how you choose to store your points ('geometry' or 'geography').
See ST_Distance from the PostGIS docs for excellent examples of measuring distance using both geometry and geography points. Note, if you wish to calculate projected map distances you will need to pick an appropriate map projection and use ST_Transform to project your points to the appropriate spatial reference system (currently in SRID 4326- "GPS" coordinates). For only a few points the difference won't be at all noticeable, but once you start doing lots of more complex spatial queries, the difference can be significant. PostGIS has a lot more functions for geometry types than for geography types which may influence your decision. Also see ST_DistanceSpheroid for another possibility for calculating distance from Lon/Lat coordinates.
To start with, I'd store your points as 'geography' to simplify your experiments. Your distances will then be 'great circle' calcs in metres and you won't have to worry about projections initially.
I'm a complete illiterate when it comes to working with geographical data, so bear with me.
For our application we will be tracking a fairly large amount of rapidly changing points on a map. It would be nice to be able to cache the location of these points in some kind of map-tile structure so it would be easy to find all points currently in the same tile or neighbouring tiles, making it easier to quickly determine the nearest neigbours and have special logic for specific tiles, etc.
Although we're working for one specific (but already large) location, it would be nice if a solution would scale to other locations as well. Since we would only cache tiles that concern the system, would just tiling the enitre planet be the best option? The dimensions of a tile would then be measured in arc seconds/minutes, or is that a bad idea?
We already work with Postgres and this seems like something that could be done with PostGIS (is this what rasters are?), but jumping in to the documentation/tutorials without knowing what exactly I'm looking for is proving difficult. Any ideas?
PostGIS is all that you need. It can store your points in any coordinate reference system, but you'll probably be using longitude/latitude. Are your points coming from a GPS device?
PostGIS uses GIST indexing, making the search for points close to a given point quite efficient. One option you might want to look at, seeing that you are interested in tiling, is to "geohash" your points. Basically, this turns an (X,Y) coordinate pair into a single "string" with a length depending on the level of partitioning. Nearby points will have the same geohash value (= 1 tile) and are then easily identified with standard database search tools. See this answer and related question for some more considerations and an example in PostgreSQL.
You do not want to look at rasters. These are gridded data, think aerial photography or satellite images, weather maps, etc.
But if you want a more specific answer you should give some more details:
How many points? How are they collected?
Do you have large clusters?
Local? Regional? Global?
What other data does this relate to?
Pseudo table structure? Data layout?
etc
More info = better answer
Cheers, hope you get your face back
I'd like to stack the images from this map: http://earthquake.usgs.gov/regional/nca/soiltype/map/ from linear projection into a leaflet map. The source tiles are in known but nonstandard zoom levels, and leaflet maps want mercator mercator XYZ tiles. In principle, I know how to do this - I have functions for changing XY coordinates into lat-lng coordinates in the two maps, and I just need to map pixels for the target map in terms of pixels in the source map.
This is unfortunately nontrivial, as the source pixels are spread across hundreds of different image files, and I am trying to put them into hundreds more images. Is there a software package that makes this a little bit more straightforward? If there is no library for dealing with this kind of data, it seems like there really should be...
Postgis has the RT_ST_Transform method, which under the hood uses GdalWarp. So, you have at least these two options. If you use Postgis, you will need to actually register/import the images into Postgis, using raster2pgsql and then call RT_ST_Transform on each one and then dump them out again -- which could be scripted to some extent using plpgsql (Postgres's scripting language). There is something of a learning curve involved with using Postgis raster, which may be worthwhile if you plan to do any other image processing analysis. You could also write a shell script (or similar) to automate gdalwarp if you don't wish to go the Postgis route.
For a less formal method than gdalwarp (an excellent program), you can check out the Leaflet plugin Leaflet.imageTransform, that can transform and image on the fly in the browser.
I am very new in working with GIS or geometry data. I have geometry data (polygon) in oracle10g database. Is there any Spatial function to find a point inside that polygon. If not then any tool like geotools for .Net or any other API can help me. The polygon can have hole inside it. So point must be in a polygon area.
Thanks in advance for your help
Naym
Have you looked at Oracle Locator? The query syntax is awful to read, but it is capable of doing "is point in polygon" queries. You'll need to create a spatial index column on any table that you want to run a spatial query against. Reading the documentation is a must, because it is a pain to get working initially.