Tuesday, March 11, 2014

Fetching all of the AHN2 raster data with FME.



AHN2

Recently the AHN2 dataset was released to the public via the Dutch SDI (PDOK)
This was a perfect opportunity to set FME to work on this newly available resource.
This time the rasters and point cloud data was made available via an Atom feed XML.
This means that you can download the 5 meter GeoTIFF rasters and LAZ point cloud data on a national scale. 
Well I had to try that...just for a starters, to see how long it would take me to build the workspace and download the raster data.

Workspace

Building the workspace took about 5 minutes, the tricky part was to make sure you are grabbing the correct part of the XML, after that it's a walk in the park, letting FME get the data off the Internet. 
The workspace itself (4 transformers) starts with a Creator to jump start the HTTPFeatcher, that grabs the XML document.(AtomFeed)
After finding the correct XML tag and extracting the information (URL) with an XMLFragmenter the string is passed to retrieve the rasters (RasterReader).

Data

The raster data took a while longer to download but that is mainly due to the fact that the rasters need to be fetched off the Internet.


Another aspect that I wanted to test was the ability to save the data, so I made use of the (very much welcomed back!!) capability to save the data directly from the Data Inspector.
The FFS is the native FME format, which supports vectors and rasters. The ability to compress the data was applied to see how compact such a big dataset can be made.
After about 15 minutes the Data Inspector happily reported finishing the job of saving the data, I was pleasantly surprised to find out that only about 6 gigabyte of space was necessary.


Results and development

 After downloading the data, I wanted to make the workspace easy use to use and flexible for any spatial selection (My guess is that not many people are interested in the all dataset, but mainly the data in a specific area of interest)

AHN2 raster data.
So what can be better than combining additional services containing rasters bounding boxes and boundaries.
That way you can select your area of interest be it a municipality border or a selected area of interest.

The Dutch SDI provides the possibility to download data in much the same way, but once you have the data in your FME workbench, you can do much more that just download.

This is actually where it starts to get interesting, the opportunities that the height data provides are numerous.

More about downloading the point cloud data and combining the different SDI services on the next post.

By the way did I mention the the rasters are read from a zip file? Well no because that is so 2013 ;)