I'm trying to draw a map with a lot of markers on it. Just say more than 3000 markers, and this is taking a very long time to process and is using a lot of memory.
But I have the same map on Google Earth and this open very quickly. Somebody knows a way to speedup the process using gmLib?
Take a look at RTree structures.
R-trees are tree data structures used for spatial access methods,
i.e., for indexing multi-dimensional information such as geographical
coordinates, rectangles or polygons.
A common real-world usage for an R-tree might be to store spatial
objects such as restaurant locations or the polygons that typical maps
are made of: streets, buildings, outlines of lakes, coastlines, etc.
and then find answers quickly to queries such as "Find all museums
within 2 km of my current location", "retrieve all road segments
within 2 km of my location"
Queries like the one you expect will become almost immediate... :)
I use the RTree extension available in SQLite3. Our Open Source framework interfaces this kind of virtual tables with Delphi classes. BTW it works from Delphi 6 up to XE5.
If you are afraid of using a RTree, just ordering the data in order will help a lot searching e.g. via a binary search algorithm.
Related
I have been using the GMLib for Google Maps operations for some years now without any problems and have made some interesting things if I must say so.
But now I am working on another project where I have a full address and needs to geocode that, but I don't need to show it on a map since I just need the latitude and longitude to calculate a QRA locator (it is a system of map grids used by HAM operators all over the world)
I think I could speed up the process by not using a map since it takes time to load every time.
Are there any components or libraries that could help me or isn't it possible to do at all.
Assume that you have the boundaries of states/counties of any country in a text file as follows:
State \t State Name \t Lat/Long of entire State Boundary(comma separated).
I want to to store this information in a data structure** and then given a lat-long, retrieve the state.
I don't want to use APIs and don't want to do the brute force approach (that is, build a polygon for each state and then do a point in polygon algorithm until a hit)
With my limited knowledge, I think KD-Trees or R-Trees is the way to do? Although both of the seem like good choice, I am not sure which one to use. It would be very helpful if you can provide a detailed explanation - from creating the Data Structure to performing the search.
I am more interested in the counties than states because of their finer granularity. May be it is worth stopping the tree building at a larger granularity and then do a point in polygon approach for all the counties in that granularity (Minimum bounding region). Conceptually this seems doable, but I am not sure how to implement this.
If you haven't already chosen a Geospatial friendly database, pick Postgis. Mysql 5.7 will also do the trick but Postgis is more mature and feature rich.2
Download the world borders shapefile.
Import the shapefile into postgis or into mysql
Make use of the ST_Within function available in both mysql and postgis to determine if a given point is inside any country and to retrieve the name or other information for that country.
Note that the ST_within query is fast, and you don't need to do a lot hard on your own. This is a one liner.
Setting up the database and importing the database maybe hard work, but you will have to do that anyway even if you come up with a home made solution.
I have an application that successfully uses a pre loaded tile cache of Open Street Map .png files for a small city area about 20km x20km to support the presentation of tourist information on the web, iPad and iPhone. It is written in HTML5 and uses MoSync to create the wrapper to deliver it on the mobile devices.
This approach works well for cities but I would like to extend the app to work in countryside areas (in the UK initially) where if I could access it, Ordnance Survey mapping 25000,50000 and 250000 would deliver a much better user experience.
My specific questions are:
How do I get hold of topographic tiles?
Can I get tiles that have the same slippy map structure as OSM.
Can I use Ordnance Survey as a source for the UK and if so is it a one off license fee?
What zoom levels are available? I expect 25000, 50000 and 250000. Is 100000 available?
What formula do I use to identify the specific tile from a lat and long pair?
Will all the tiles at a specified zoom level be the same delta lat and delta long? If not how do I tile them?
Answering a few of your questions:
There are several OSM based maps with topographic elements. Take a look at the list of tile servers and the list of OSM based services. Remember to check each usage policy first before using them in your application.
For determining the filenames of the slippy map for a given latitude, longitude and zoom level, read the slippy map tilenames page in the OSM wiki.
I am developing iOS 5 app which I want to communicate with server providing information about the nearby places for a given location: places locations and annotations. I want to use MapKit to populate my map with this information.
I didn't find any straightforward information regarding the following questions:
Does MapKit has tiles functionality (Google Maps way) out-of-the-box and do I need to work on it additionally, if not?
What is the best practice of retrieving places information (markers positions and annotations) from server?
Is it possible to cache this information so an user can see the nearby places of "his city" in offline mode?
Actually questions 2 and 3 are interrelated: they both address the problem of not retrieving an information (locations + annotations) that is already on map multiple times.
Hopefully I am not overlooking something obvious here.
Thanks!
Update 1: (Regarding places, not maps) More specifically I am interested in, how should I create a "hand-crafted" logical tiles for regions containing the places I fetch from the server, so they would not require refetching themselves when user scrolls the map? I know I can dive into implementing this functionality myself. For example, should I write the places just fetched to a local storage using Core Data immediately after fetching them or organize some queue? Or how could I know when I need to perform a request about the specific region on server and when I just fetch local data that is already on the device? I just want to know, are there any recommended approaches, best practices? Hopefully, I wrote it clear here.
Update 2: I am wondering about best practices here (links, example) not to start creating all this (points 2+3) from scratch. Are there any frameworks incapsulating this or good tutorials?
#Stanislaw - We have implemented the functionality you describe in an app called PreventConnect for one of our clients. The client already had some data stored out in a Google Fusion table. We extended their existing solution by adding another Google Fusion table which stores the geocoordinates for a number of locations. All this being said, to answer your questions...
1) The map portion itself is pretty out of the box, the tiles and what not, but you'll need to do some coding to get zoom extents, pin drops, annotations, and things like that working the way you expect them to work.
2) We found the Google Fusion solution to be quite effective. If you don't want to use Google Fusion there are other cloud database providers like StackMob, database.com, and many others. Google is free and they have an iOS SDK that makes communicating with Google Fusion pretty simple.
3) Absolutely! We cache much of the data in a Core Data store locally on the device. This greatly improves performance and responsiveness.
Time to write a solid answer to this my question (I could have it written a year ago but somehow I lost it from my mind).
Does MapKit has tiles functionality (Google Maps way) out-of-the-box and do I need to work on it additionally, if not?
The answer is yes: MapKit does have it. The keywords here are overlays (MKOverlay, MKOverlayView and others). See my another answer.
See also:
WWDC 2010 Session: Customizing Maps with Overlays,
Apple-WWDC10-TileMap.
What is the best practice of retrieving places information (markers positions and annotations) from server?
Actually since then I didn't learn a lot about "best practices" - unfortunately, nobody told me about them :( - that is why I will describe "my practices".
First of all, there are two strategies of populating a MapKit map with places:
The first strategy is about populating your map with the places by demand: imagine you want to display and see all places nearby (for example, no more than 1km from current user location) - this approach assumes that you ask your server only the places for the box you are being interested in. It means something like: "if I am in Berlin (and I expect 200 places for Berlin), why should I ever fetch the places from Russia, Japan, ... (10000+ places)".
This approach leads to relying on "tiles" functionality that question N1 address: Google maps and Apple maps are usually drawn using 'tiles' so for your "Berlin" portion of map you rely on corresponding "Berlin" tiles that are drawn by MKMapView - you use their dimensions, to ask your server only the places within the "Berlin" box (see my linked answer and the demo app there).
Initially this was the approach I've used and my implementation worked perfectly but later I was pushed to use second approach (see below) because the problem of clustering appeared.
The second strategy is to fetch all the places at once (yeah, all this 10000+ or more) and use Core Data to fetch the places needed for the visible portions of map your are interested in.
Second approach means, that during the first run you send your server a request to fetch all places (I have about 2000 in my app). Important here is that you restrict the fields you fetch to only geo-ones that you really need for your map: id, latitude, longitude.
This 'fetch-all' fetch has a significant impact on my app's first start time (On "the oldest" iPhone 4, I have near 700ms for the whole Fetch + Parse-JSON-into-Core-Data process, and extensive benchmarks show me that it is Core Data and its inserts is a bottleneck) but then you have all the essential geo-info about your places on your device.
Note, that whatever strategy you use, you should do a process of fetching these geo-points efficiently:
Imagine Core Data entity Place which has the following fields structure (preudo-Objective-C code):
// Unique identificator
NSNumber *id,
// Geo info
NSNumber *latitude,
NSNumber *longitude,
// The rest "heavy" info
NSString *name,
NSString *shortDescription,
NSString *detailedDescription, etc
Fetching places efficiently means that you ask only your place records geo-data from your server to make the process of this mirroring as fast as possible.
See also this hot topic: Improve process of mirroring server database to a client database via JSON?.
The clustering problem is out of scope of this question but is still very relevant and affects the whole algorithm you use for the whole proces - the only note I will leave here is that all the current existing clustering solutions will require you to use second strategy - you must have all the places prepared before you run into the clustering algorithms that will organize your places on a map - it means that if you decide to use clustering you must use strategy #2.
Relevant links on clustering:
WWDC 2011 Session: Visualizing Information Geographically with MapKit,
How To Efficiently Display Large Amounts of Data on iOS Maps,
kingpin - Open-source clustering solution: performant and easy-to-use.
Is it possible to cache this information so an user can see the nearby places of "his city" in offline mode?
Yes, both strategies do this: the first one caches the places you see on your map - if you observed Berlin's portion of map you will have Berlin part cached...
When using the second strategy: you will have all essential geo-information about your places cached and ready to be drawn on a map in offline mode (assuming that MapKit cached the map images of regions you browse in offline mode).
I want to convince some clients to use MapServer and OpenLayers. Please can anyone suggest attractive websites to show off the possiblities!
The clients will be impressed by:
A density map (otherwise known as a heat map, colour-shaded grid coverage, contour plot...).
The ability for the user to download the underlying data for the density map, restricted to the area being viewed, in some format such as netCDF.
Standard OpenLayers stuff. Zooming, panning, scale bar, overview map...
Different base layers. Could be WMS, Google, Bing...
Searching for a placename, map is panned to display the place.
Exposing the heatmap data for other people to use in mashups as WMS or WCS
MapServer.org is back up but demo.mapserver.org seems to be down right now :( But from memory their examples didn't have the "wow" factor. The OpenLayers examples demonstrate only one or two features per example - I want something to wow the clients by showing all the capabilities in one example.
PS If you have good examples that use some other open source tools, post them by all means. But just JavaScript please: customer says no rich client.
EDIT Come on StackOverflow, someone must have an example that uses a density map?? I'm even offering a bounty now...
Note this answer is no longer relevant. The open source maps have since been replaced with a commercial alternative by a different company
http://maps.seai.ie/wind/ - mapping onshore and offshore wind speeds and farms in Ireland
http://maps.seai.ie/geothermal/ - mapping geothermal temperatures in Ireland, and borehole data
uses WMS services (and TileCache) for all the layers, so can be accessed by other client GIS's (well once I've set up metadata etc..)
has a variety of different base maps to choose from
built using MapFish / ExtJS
has drop down gazetteers for County and Townland (an Irish administrative unit)
all the basic map navigation tools and a simple info tool
right click on a layer to set transparency
uses MapServer opensource back-end, plus SQL Server 2008
The systems (and a third more complex Bioenergy Intranet system) got a mention here: http://www.geoconnexion.com/uploads/renewableenergy_intv9i4.pdf
http://haiticrisismap.org/ openlayes + geoxt
would it be possible to create a template map for the client with a bunch of data on it, census, socio, create some simple fake buffers.
Maybe have a look at the HeatMapAPI for Google Maps (not sure you'll wow the client with that though).
Another density map: http://maps.glassfish.org/server/ (showing the use of GlassFish around the world).
We're using the OpenLayers Heatmap layer, mostly because (for us) it handles large data volumes better than the Google Map version (your mileage may vary)
http://www.patrick-wied.at/static/heatmapjs/demo/maps_heatmap_layer/openlayers.php
By large data volumes, I mean location datasets with 100K+ rows
It also works nicely as an ASPX page with dynamic realtime data retrieval from an SQL Server database. I've used a stored procedure to pre-process the data into the array format, grouped by Latitude & Longitude.
For those that need a translation table to convert their UK Postcodes into Latitude & Longitude, here's a good source:
http://www.doogal.co.uk/UKPostcodes.php
The OneGeology Portal (http://portal.onegeology.org/OnegeologyGlobal/) has been online for about 10 years, currently running OpenLayers 2, with an OpenLayers 3 version in development.
The portal attempts to create a geological map of the world by pulling together disparate OGC services provided by data suppliers (mostly Geological Surveys) from across the globe. The portal provides access to data from WMS, WFS (simple and complex feature), and WCS. The portal uses CSW to help manage which functionality is available to a user, and provides the ability to style WMS layers through the application of custom SLD. Map contexts can be saved, shared and loaded using WMC.
There is a gazetteer to help you zoom to a location of choice, the ability to change projections, and scales, and the ability to create a KML file to allow the service to be used in Google Earth. Transparency can be changed on all layers.
There are currently 353 layers.
When the OneGeology project started, all documentation was geared to the support of services provided by MapServer, and many of the services in the portal are MapServer services. However, because the portal utilises open standards, any software that can provide services to those standards can be included.
This is an example of a classified grid generated in MapServer and displayed by OpenLayers: https://maps.greenwoodmap.com/sublette/mapserver/map#zcr=1/2690000/1170000/0&lyrs=slopesZ,townlim,ownership,roads. The raw, unclassified slope data can also queried by map click.