# vmx

the blllog.

## WhereCampEU 2011 Berlin

2011-05-29 22:27

The WhereCampEU 2011 is just over now, so it's time to get my impression and notes from the sessions written down. But first I'd like to thank all the organizers and attendees for this great event and the geobeers in the evenings.

## Geo Databases

The WhereCamp is also a chance to meet people you haven't seen for a long time. Exactly this was the case with Shoaib Burq. We know each other from being a member of the FOSS4G 2009 organizing committee.

As there were still a few free slots, we decided to make session that is simply called "Geo Databases". I didn't expect many people to show up, as there were other sessions with way catchier names.

I ran late as I didn't find the room where my session was supposed to be. But luckily Shoaib was already presenting a rough outline on what will be talked about (we haven't talked about what we want to do upfront). So I happily joined the crowd and started to moderate things a bit. And it was just amazing, the room was packed with people even sitting on the floor. A rough guess would b,e that it was half of the attendees.

We discussed a bit about one of my favourite topics, the question of how much should be done within a geospatial database and what should be done outside of it. It then led to the problem that doing a lot within the database is easy (and fast) on a single instance, but as soon as you want to distribute your database, you might get into trouble.

To conclude, the atmosphere was good and people seemed to have enjoyed it (at least some were telling me so :) I'm happy that it went this well. Shoaib has kindly taken some notes and put on Github.

## Web Mapping Libraries

On the second day the program wasn't as packed as on the first day, so I decided to make another session called "Web Mapping Libraries". The Again I didn't expect too many people to show up and this time I was right. It was a good crowd nonetheless.

What I wanted to find out was why people create new web mapping libraries instead of just improving existing ones like OpenLayers. This was also triggered by Slide 54 from Peter Batty's talk, where he compares OpenLayers to Google Maps. The two things that were catching my attention were "lightweight" and "extra mobile features". Those two can be solved. Eric Lemoine demonstrated a 29KB (gzipped) version of OpenLayers including the mobile features that were added at the Lausanne Code Sprint.

In the session it was just great to hear the impressions for what I call "web neogeo people" (people are web developers, designers and general people that like to visualize data) as opposed to "old school GIS people" (that know all kinds of OGC standards and dream about the axis confusion at night).

Things we've identified were (photo version):

• Documentation
• Default Look
• Usability
• Examples are not good
• No explanation of the general architecture

### Documentation

The main source of documentation are the API docs. They describe every function of the library. One problem is that it isn't really clear what exactly you can pass in when one parameter is an options object (Example.

The lack of documentation with a nice introduction was also mentioned. Though I don't fully agree, there is some really nice documentation in prose, but it seems that people easily miss it (I especially like e.g. the page about Spherical Mercator).

### Default look

I agree that the default look of OpenLayers looks a bit out dated. The main buttons look like from the early 2000's and the layer switcher isn't nice either.

On the one hand, you can change the look if you want to (example (scroll down)), or code the controls with any UI library you'd like to use (this is what GeoExt/MapQuery does).

### Usability

I'm not really sure what this one was about, but I think it was about the complexity of OpenLayers. You need to have quite a bit GIS knowledge before you can get started. Don't get me wrong, I love OpenLayers for what it does and it's huge amount of features, though it comes to a price for newbies.

Again this is where I think GeoExt/MapQuery can help. They can build an easy to use API around the most common functionality like: display a GeoJSON file on a Google base map that shows a popup when I click on the geometry.

### Examples are not good

It's nice to have a whole bunch of examples, though in the case of OpenLayers they are a bit misleading. I use them a lot to see how things work. Though they are not always well drafted idiomatic OpenLayers examples, but rather some source showing how a specific feature works. And this is exactly what they are. If you implement a new feature, you create API documentation and a working example.

For me they are more like acceptance tests, rather than good howtos for newbies.

### No explanation of the general architecture

This one was mostly about "how do things work". One point was about vector layers. They are really powerful and you can compose them out of several parts with things like strategies and formats. It's not easy to understand how they fit together.

I think there was also another point, but I don't recall it. Let me know if you were at the session and remember it :)

## Conclusion

I had a great time at the WhereCampEU 2011 and it was definitely worth going there. If you have anything to add to the notes about the session, please do so.

Categories: en, GeoCouch, OpenLayers, MapQuery, conference, geo

## FOSSGIS, GeoCouch and MapQuery

2011-04-19 22:27

Two weeks ago I had the chance to give a talk about GeoCouch and MapQuery at the FOSSGIS 2011. Most of the people who read this Blog are probably aware of GeoCouch, but not so much of MapQuery. For me these two projects are tightly connected and therefore deserve a quick introduction/update.

## GeoCouch

GeoCouch, a spatial index for CouchDB gains, more and more attention. One of the reason is that the installation recently got way easier for developers as well as for normal users. You now can install GeoCouch as an extension right next to your already existing CouchDB instance. You may also download a binary of Couchbase-Server, which already includes GeoCouch. And finally there's the brand new Iris Couch hosting as well (previously known as the CouchOne hosting). So getting started with GeoCouch is easier than ever before.

Some people might have wondered about the state/future of GeoCouch, especially after the merger of CouchOne with Membase to Couchbase. I will keep on developing GeoCouch at Couchbase and it is (as it always was) fully open source licensed under the Apache 2.0 License.

The new home for the latest source is the Couchbase Github repository.

### OpenStreetMap

The FOSSGIS was also about OpenStreetMap. The idea to put OpenStreetMap data into GeoCouch is very sensible, but wasn't really done (AFAIK) in a big fashion. Luckily Jochen Topf from Geofabrik told me about his Projekt Osmium, which makes it possible to process OSM data with JavaScript. There is already a script to output a Shapefile, so it should be really easy to output GeoJSON, which could be consumed by GeoCouch. So if you (who are currently reading this) have some spare time, please give it a go :)

## MapQuery

MapQuery is a web mapping framework that builds on OpenLayers and jQuery. The goal is a framework that is just as easy to use as jQuery combined with the power of OpenLayers. It's meant for people that just want to get started with web mapping, but also for those who have already knowledge about OpenLayers and want to have easy integration into their jQuery application.

I was able to show a quick demo of the MapQuery API at the FOSSGIS. I won't publish it here, as things are about to move fast. After over one year of discussions about MapQuery and only little code contributions, it seems that we are finally getting somewhere. That feels so good :)

The wonderful EduGIS is build on an early version of MapQuery (source code), but will be merged with the most recent version of my fork.

Other big news is that the WhereGroup hired Christian Wygoda, who is a committer of the MapQuery project. This also means that Mapbender 3 will use MapQuery.

And finally I've also met a developer of a another company that was building a big mapping application based on OpenLayers and jQuery. I don't want disclose it here, as the code isn't open source yet, but the developer told me that it should be easily possible. I will keep in touch with them and hope they will contribute their code to MapQuery.

To get to a conclusion about MapQuery. If you want to stay in touch with the project, please subscribe to the official mailing list, this is where things are happening (there's also the little attended IRC channel #mapquery on freenode). If you want to be a user of MapQuery, you should be patient and wait a bit. If you plan to contribute, you can start now. The currently biggest item is moving the EduGIS MapQuery code base over to the MapQuery version of my fork. The "documententation" are the demos.

## FOSSGIS

As people started to asked about the slides from my presentaion at FOSSGIS, here they are.

FOSSGIS was a really awesome event, where I met a lot of new people, but also a lot of friends I haven't seen in a while. I'm really looking forward to next year's conference, but also hope that I might see many of the people at this year's FOSS4g in Denver.

Categories: en, CouchDB, GeoCouch, MapQuery, geo

## How I met CouchDB

2010-07-14 22:27

It was a Saturday in late April 2008, I was sitting on my Laptop in my 5m² room down under. Chatting with some German people I used to chat with for about 8 years by that time. Suddenly I discover that Jan is there, who I haven't talked with for years. Wondering why he was in there, he replied that he wanted to brag about his apache.org email address. This is how I found out about CouchDB.

After several long discussions with Jan I finally wrapped my head around the document oriented concept. I was blown away, it was exactly what I would have liked to use on so many occasions at my one year internship at a geospatial company. Though CouchDB wasn't ready, I needed spatial indexing. One week later I had a first idea of how such an extension might look like.

And only 2 years later I'm really involved in CouchDB and people actually start using GeoCouch :) I'd like to use this blog post to thank the developers and the whole community, it's been a great time and the IRC channel just kicks ass. You all helped to make CouchDB 1.0 possible!

Categories: en, CouchDB

## Bolsena hacking event

2010-06-11 22:27

The OSGeo hacking event in Bolsena/Italy was great. Many interesting people sitting the whole day in front of their laptops surrounded by a beautiful scenery and nice warm sunny weather. It gets even better when you get meat for lunch and dinner.

I had the chance to tell people a bit more about CouchDB and Couchapps,

One project I haven't heard that much before of was Degree. They build the whole stack of OGC services you could imagine. For me it was of interest that they have a blob storage in their upcoming 3.0 release. The data isn't flattened into SQL tables but stored as blobs. This sounds like good use for a CouchDB backend in the future.

I was working with Simon Pigot on a GeoNetwork re-implementation based on CouchDB using Couchapp. We got the basic stuff like putting an XML document into the database, editing it and returning the new document, as well as fulltext indexing with couchdb-lucene work. Next steps are improving the JSON to XML mapping and integrating spatial search based on GeoCouch.

The event was really enjoyable, thanks Couchio for sponsoring the trip, thanks Jeroen for organizing it, and thanks all other hackers that made it such a awesome event. Hope to see you next year!

Categories: en, CouchDB, JavaScript, geo

## FOSS4G 2010: I'm speaking

2010-05-21 22:27

I did it! I'll speak at the FOSS4G Conference 2010 (Free and Open Source Software for Geospatial Conference), 6th–9th September in Barcelona about “GeoCouch: A spatial index for CouchDB”. As soon as the abstract is available online I'll link to it. Hope to see you there!

Categories: en, GeoCouch, CouchDB, Erlang, geo

## Non-validating WKT parser for Erlang

2010-05-14 22:27

The upcoming OpenSearch Geo specification will add support for querying with WKT (Well-Known Text). As I plan to support this specification in GeoCouch, I was in need of a WKT parser written in Erlang. I tried several ways to write this parser, but I ended up with writing it manually, based on the ideas of the fabulous MochiWeb JSON2 Parser

The parser is meant for fast parsing, it is non-validating. This means that it parses only valid WKT and all other strings that seem to be valid, but are not. The grammar is simplified to (in EBNF as used for the XML spec):

wkt ::= item | string  '(' space* item (comma item)* ')'
item ::= string (geom | list | nested_list | item | 'EMPTY')
nested_list ::= space* '(' list (comma list)* ')' | '(' nested_list+ ')'
list ::= '(' geom (comma geom)* ')'
geom ::= space* '(' coord (comma coord)* ')'
coord ::= space* number (space+ number)*
number ::= integer | float
integer ::=  ('-' | '+')? [0-9]+
float ::= ('-' | '+')? [0-9]+ '.' [0-9]+ exponent?
exponent = 'E' ('-' | '+')? [0-9]+
string ::= [a-zA-Z]+ (space* [a-zA-Z])*
space :== #x20
comma :== ',' space*


I hope I got the grammar right, leave a comment if not. This means also strings like this(is(10 20), a test EMPTY) would be parsed to:

{this,[{is,[{10,20}]},{'a test',[]}]}


A validating parser would be much slower as it would also need to perform checks on the geometry, e.g. for polygons whether interiors are really within the exterior ring or not.

The general rule is, a list of coordinates is transformed to a tuple, a list of coordinates to a list. The geometry name will be an atom. Here's an example for a polygon:

wkt:parse("POLYGON ((102 103, 204 205, 306 107, 102 103),
(12 13, 24 25, 36 17, 12 13),
(62 63, 74 75, 86 67, 62 63))").
{polygon,[[{102,103},{204,205},{306,107},{102,103}],
[{12,13},{24,25},{36,17},{12,13}],
[{62,63},{74,75},{86,67},{62,63}]]}


In case you're getting excited now, the source is available at Github, realeased under the MIT License.

If someone plans to write a validating WKT parser for Erlang (please let me know), I propose using neotoma it's really a nice "packrat parser-generator for Erlang for Parsing Expression Grammars (PEGs)".

Categories: en, GeoCouch, Erlang, geo

## GeoCouch: The future is now

2010-05-03 22:27

Update: This blog entry is outdated and kepts for historical reasons. Please do always check for newer blog posts. The up to date information on how to install and use GeoCouch can be found in its README.

An idea has become reality. Exactly two years after the blog post with the initial vision, a new version of GeoCouch is finished. It's a huge step forward. The first time the dependencies were narrowed down to CouchDB itself. No Python, no SpatiaLite any longer, it's pure Erlang. GeoCouch is tightly integrated with CouchDB, so you'll get all the nice features you love about CouchDB.

### Current implementation

Thanks to the feedback after the FOSS4G 2009 and "GeoCouch: The future" blog entry" it was clear that people prefer a simple, yet powerful and tightly integrated approach, rather than having to many external dependencies (which was a showstopper for quite a few people).

I implemented an R-tree (I call it vtree as the implementation is subject to change a lot) from scratch. The reason why I haven't used the already existing R-Tree implementation available at Github is that I needed something to learn Erlang, it doesn't contain test or examples and that it is always a good idea to implement a data structure yourself to understand the details/problems. My implementation is far from being perfect but works good enough for now. The vtree is implemented as an append-only data structure just as CouchDB's B-trees are. Currently it doesn't support bulk insertion.

If you want to know details on how to create your own indexer, have a look at my Indexer tutorial.

### Feature set

Following the "Release early, release often" philosophy currently only points can be inserted, the only supported query is a bounding box search. Though other geometries should follow soon.

### Using GeoCouch

GeoCouch is now hosted at Github. Giving GeoCouch a go is easy:

git clone http://github.com/vmx/couchdb.git
cd couchdb
./bootstrap
./configure
make dev
./utils/run


To try the spatial features when it's up and running is easy as well. Just add a spatial property and a named function to your Design Document as you would to for show or list functions:

function(doc) {
if (doc.loc) {
emit(doc._id, {
type: "Point",
coordinates: [doc.loc[0], doc.loc[1]]
});
}
};


All you need to do is emitting GeoJSON as the value (Remember that point is the only supported geometry at the moment), the key is currently ignored.

curl -X PUT http://127.0.0.1:5984/places
curl -X PUT -d '{"spatial":{"points":"function(doc) {\n    if (doc.loc) {\n        emit(doc._id, {\n            type: \"Point\",\n            coordinates: [doc.loc[0], doc.loc[1]]\n        });\n    }};"}}' http://127.0.0.1:5984/places/_design/main


Before a bounding box query can return anything, you need to insert Documents that contain a location.

curl -X PUT -d '{"loc": [-122.270833, 37.804444]}' http://127.0.0.1:5984/places/oakland
curl -X PUT -d '{"loc": [10.898333, 48.371667]}' http://127.0.0.1:5984/places/augsburg


And finally you can make a bounding box request:

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/points/%5B0,0,180,90%5D'


This one should return only augsburg:

{"query1":[{"id":"augsburg","loc":[10.898333,48.371667]}]}


### Next steps

The development of GeoCouch was quite slow in the past, but it gets up to speed as my diploma thesis (comparable to a master's thesis) will be about GeoCouch. Additionally Couchio kindly supports the development.

The next steps are (in no particular order):

• Better R-tree (better splitting algorithm, bulk operations)
• Supporting more geometries
• Polygon search
• Improving CouchDB's plugin capabilities

### Thanks

I'd like to thank all the people that kept me motivated over the past two years with their tremendous feedback. Special thanks go to Jan Lehnardt for getting me onto the Couch, Cameron Shorter for introducing me into the geospatial open source business and all people from Couchio for the great two weeks in Oakland.

Categories: en, CouchDB, Python, Erlang, geo

## Processing PDF files: Auto advance

2010-02-23 22:27

Sometimes you need a PDF file that auto advances (auto flip, slide show) pages after a certain amount of seconds. For example for presenting a Lightning Talk the Ingnite way. There are several ways to achieve this. Today I've spent hours to find the best way.

You could just hope that your favourite PDF viewer supports changing slides automatically in a certain interval (Evince doesn't). But you never know which viewer will be used when you rely on other people's computers. The next step is obvious, try to get the PDF file itself to auto advance. It is possible as Adobe Acrobat supports such a setting (it seems that even Acrobat Reader does, though I can't find that option in my one under Linux), I just need to find out how.

After some further research I found out that Latex' hyperref package supports it as well (no, I don't speak Czech). So I made some minimal Latex Beamer presentation to give it a try. The important notice that the \hypersetup{pdfpageduration=n} must be the first item within a \begin{frame} was found in some presentation guidelines. Guess what? It even works with Evince (tex file, PDF file).

I'm getting closer. Though my problem is that I create my slides with Inkscape (resp. Inkscape Slide), so I can't really user Latex Beamer for it. But the previously mentioned presentation guidelines also mention the /Dur entry in the PDF page object. So it should be easy to add it manually. And it really is. A quick search through the PDF file generated by Latex you can see that /Dur occurs a close to /MediaBox. After adding those /Dur 2 to my original presentation PDF file right after \MediaBox it auto flipped every 2 seconds.

I could have written a simple script that adds it to the PDF at the right place, but that sounds pretty fragile. A better approach would be to use a PDF library that is meant for manipulating PDF files. As my favourite programming language is Python at the moment, I came across pyPdf. A quick look at the internals showed that it contains everything I need.

Here's my final solution for the problem of creating auto advancing PDF slides. A small script that does exactly what I need (and not more). I've used the Python 3 version of pyPdf, but the script should look similar for Python 2.x.

#!/usr/bin/env python3.1 # Copyright (c) 2010 Volker Mische (http://vmx.cx/) # Licensed under MIT. import sys from pyPdf import PdfFileWriter, PdfFileReader from pyPdf.generic import NameObject, NumberObject def main(argv=None): if argv is None: argv = sys.argv if len(argv) != 4: print('Usage: setduration.py [duration-in-seconds] [input-pdf]', '[output-pdf]') return pdfin = PdfFileReader(open(argv[2], "rb")) pdfout = PdfFileWriter() for page in pdfin.pages: page[NameObject('/Dur')] = NumberObject(argv[1]) pdfout.addPage(page) outputStream = open(argv[3], "wb") pdfout.write(outputStream) if __name__ == '__main__': sys.exit(main()) 

Categories: en, Python

## GeoCouch: The future

2009-12-20 22:27

GeoCouch started as a proof of concept and was heavily rewritten for the 0.10 release. As more and more people got interested, I got feedback to see what people really want/need. And now it's time to determine the future of GeoCouch. It's your chance to shape the future. In this blog entry I'll explain my ideas for the future, but I'm more than happy to get further ideas/complains from you. So please check if my ideas match your use-cases for GeoCouch.

### Stripping it down

GeoCouch needs an external spatial index, at the moment I use SpatiaLite for it, but a PostGIS backend would be easily possible. My inital idea was that it is better to use the existing power of spatial databases, rather than reinventing the wheel. I though I could use all the power they have, that I can even use them for complex analytics, but I can't. As I only store the geometries, I need to “ask” CouchDB for the attributes (no, I don't want to store attributes in my spatial index).

If I don't use the full power of the spatial databases, but only a small fraction, there might be better solution. Therefore I propose that GeoCouch will use a simple spatial index for storing the geometries, not a full blown spatial database. I haven't decided yet which one it'll be, but I really think about moving this part to Erlang (I know that quite a few people would love that move).

You will loose functionality like reprojection. The spatial index won't know anything about projections. So GeoCouch won't be projection aware anymore, but you application still can be. For example if you want to return your data in a different projection than it was stored, you do the transformation after you've queried GeoCouch.

You would also loose fancy things for geometries, like boolean operations on them. But this is something I'd call complex analytics, and not simple querying.

GeoCouch would only support three simple queries: bounding search, polygon search and radius/distance search. If the search would be within a union of polygons, let's say all countries of the European Union, you would simply make the union operation before you query GeoCouch.

### Complex analytics

What I call “complex analytics” is things like: “return all apple trees that are located with a 10km range around buildings that have are over 100m high, but only in countries with a population over 50 million people” is not possible with GeoCouch as you would need the attribute values as well. Those are stored in CouchDB, so you would need to request them. What GeoCouch only supports is a simple: give me all IDs within a bounding box/polygon/radius.

### Conclusion

Simple requests are needed for everyday use, thus they should be incredibly fast. Complex analytics don't necessarily need to handle thousands of requests per second, in most cases they don't even need to be processed in real-time. I'd like to see some layer build above GeoCouch, so CouchDB can even be used for analytics (which is a thing I wanted to have right from the start).

This means that GeoCouch will be mainly for high performance and massive sized projects that need some simple spatial bits, what I think the majority of users need.

If you either think you really need only those simple queries, but you want them to be fast, or you think this is wrong, that you need dynamic reprojection I can only invite you to leave a comment below or drop a mail to volker.mische@gmail.com. Thanks.

Categories: en, CouchDB, Python, geo

## FOSS4G 2009: “Geodata and CouchDB” presentation is online

2009-11-17 22:27

The final wrap-up of the FOSS4G 2009, my presentation on “Geodata and CouchDB” is available online in several formats. It should also be of interest for people who are new to CouchDB as huge parts of the talk are an introduction into CouchDB.

Categories: en, CouchDB, Python, geo