[GIS] Web mapping application with time slider and raster data

rastertimesliderweb-mapping

I need to create a web mapping application that can show raster layer of historical maps with a time slider.

Basically, something like this: http://goo.gl/GYHOX

I have different maps of different years of the same are, that can be showed on a time series and moving on with a time slider. The interface can be simple, the important thing is the time slider.

I have programming experience only in HTML/CSS, little of PHP.

Any suggestions of which tools to use? I had a look at TileMill but the problem is the time-slider that I have no clue on how to build it.

Thanks in advance for who will help me.

Best Answer

Have you tried inspecting the page's source (e.g. with Firefox's developer tools)? Looks like it's using OpenLayers and GeoExt. The time slider appears to be a custom development (check out the functions in the GeoAdmin namespace in the app.js source -- you will probably want to use something like jsbeautifier to make it readable).

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That's a question that could be the theme for a web development book because this kind of site demands aggregation of many technologies. I had exactly the same idea some time ago and then I started looking around for tools to do that kind of site. Finally I achieved a collection of packages that can do the job and here is the list, if it fits your needs than you can learn each one of then.

Server: Amazon EC2, Micro, Ubuntu Server (under free tier during development)
Web Server: Apache
SQL: PostgreSQL
WebDevelopment: Django Web Framework
AJAX (just to make things easier for Django): Dajax and DajaxIce
Jquery
Maps: GoogleAPI ou CloudmadeAPI (For OSM data).
IDE: Aptanda Studio (an Eclipse that comes with Pydev and Django extensions).
Firebug.

The core of the project is the Django framework, you will need a little python for that, but not much, if you follow the tutorial you will get what you need. I started the development using an Sqlite/spatialite database (because its easier to manage) than I when the database model was ready I switched to postgresql/postgis.

I learned a lot looking at other sites code and design, here are some examples:
http://www.mapquest.com/
http://maplink.com.br/
https://montreal.bixi.com/
http://www.gpsies.com/

[GIS] Web mapping software for a huge raster time series

EDIT: (Jan 13) I'm still seeking information on exactly how best to store a 3 dimensional 16-bit integer BIP raster and be able to efficiently query a single z-axis "column" of data. I don't want to convert it to a 32-bit format (because that would double its file size from its current 16-bit form).

Querying such a raster should not really pose large problems. You can read binary data directly using all program languages, and access is fast. Just make sure that you store your data in a file format which has all metadata in a seperate file. BIP is such a format

eg in php, assuming that the file is row major order (otherwise switch x and y), with $x and $y the position in your grid(counting from 0), $nx, $ny and $nz the number of pixels in each dimension and $nb the number of bytes per gridcell:

$fp = fopen('yourfile.bil', 'r');

fseek ($fp, $nz*$nb*($y*$nx +$x))//this is a very fast operation
// read some data
$data = fread($fp, $nz*nb);//this is also very fast

Just make sure that you access the right pixel: does counting start from top left or not, ...

Some extra info: After reading the data, you should convert it to floats. E.g.:

$dataf=unpack("f*", $data);
print_r($dataf);

In case your host does not support uploading large files, you could eg split up your bip file in eg 8 bip files.

Some more info on how I would do the rest of the website: since your data is static, you could generate a small mapviewer using gdal2tiles and openlayers. http://www.gdal.org/gdal2tiles.html In fact, since you say that "I don't really need scalability--this project is mostly to enable a few peer researchers to have easier access to my data than sending an 8GB file and loading it in ENVI."you could maybe even do without using a webgis toolbox: just let your users click on the image and catch the coordinates: http://www.emanueleferonato.com/2006/09/02/click-image-and-get-coordinates-with-javascript/

(though you should find a way to present your 5000x5000 image nicely)

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