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GSoC 09 Final Report: 07/08 – 17/08

August 17, 2009

Work done

This last week, I fixed the last found errors in the existing code. I planned to implement more pending features, but after talking with my mentors, I decided to review, fix and test the existing code. So, after manually fixing some easy-to-find bugs, I exported the GDAL autotest code from https://svn.osgeo.org/gdal/trunk/autotest and created my own test script, using python.

With this script, I successfully tested:

  • Get GDAL driver by name
  • Try to open a dataset using wrong connection strings
  • Compare, pixel by pixel, 2 WKT Rasters (1 band and 3 bands) with the original files
  • Open 2 WKT Rasters (1 band and 3 bands) and compare projection references and geotransform arrays with the original files

There are 9 tests. The necessary data for the test have been added to the gdrivers/data directory. You’ll need:

I successfully used GDAL tools like gdalinfo, gdal_translate or gdalwarp to test the code too. And I tried to use gdal2tiles, but the code needs a few modifications to accept a connection string as a valid dataset.ย  Oh, and I improved my version of gdal2wktraster script to add outdb support. I’ve updated the patch in the official osgeo ticket. So, you can download and test this new version. It still needs improvements, I’m sure.

There are two features that I couldn’t test, for different reasons, and this will be two of my first tasks after GSoC. These features are:

  • Outdb support: After modifying and testing the gdal2wktraster script to add outdb support, I realized on one bug in my code: I was trying to read the outdb raster data from IReadBlock method. But the outdb raster doesn’t necessarily have the same block arrangement than the indb raster. So, the block offsets given in IReadBlock couldn’t be valid for the outdb raster. Andย  normally, they aren’t. I realized on this error too late, and I prefered to add a comment and continue developing this feature after GSoC. In addition, you have to hack the WKT Raster code to allow outdb raster support at WKT Raster extension’s level, because this feature is under development. I chose the short path: comment the outdb checking, in rt_pg/rtpostgis.sql file, lines 532 – 535.
  • Endianess: I created the code for adding raster data to a testing table with a different endianess that my machine (little endian machine). But, when I tried to execute the “INSERT” instruction, the data was automatically changed to the correct endianess by the WKT Raster extension. I tried to hack the code, but I failed this time…

So, I have some untested features finished or partially finished (in the case of outdb support). And I finished other features, like setting raster data, or setting projection, geotransform array and nodata values. These features will be used for the creation of new WKT Rasters from GDAL driver.

Anyway, if you want to see the complete list of TODO tasks (always under revision), check the project page. I think the driver, in its current state, is a stable prototype GDAL driver, and it will be a complete one by the release of the version 1.7.0 of GDAL.

Here, you can check out the GDAL code, with the WKT Raster protoype code

Here, you can check out the GDAL autotest code, that includes the testing code for GDAL WKT Raster.

GSoC 09 conclussions

I think the GSoC 09 has been one of the greater experiences of my student’s life. For first time, I fell I’ve developed a really useful tool, in the frame of a excelent software like GDAL, an essential piece of the Open Source GIS-related world. I was a GDAL user, and now, with the permission of the GDAL team, I feel like a newbie GDAL developer. An incredible feeling ๐Ÿ™‚

During this summer of code, I’ve acquired more programming skills than in the last year. I’ve learned:

  • How to do some things in a smarter way, without “reinventing the wheel”.
  • How to organize a big software project using C/C++
  • How to write good makefiles
  • How to implement a driver, meaning how to take advantage of basic OO features like inheritance, information hiding, polymorphism, data abstraction, modularity, encapsulation. The GDAL driver architecture is an excelent tool to see these concepts working.
  • How to make questions. When you post a message to a developer list, it’s important that you provide a thorough description of the error, an example output, the version of the libraries you’re using, the configuration of your working enviroment… Obvious? Of course, but you need to be in the situation to really realize on how to ask for help.
  • Related with previous point, how to feel totally stupid when you find the error just after cliking on the “Send” button. An unique feeling ๐Ÿ™‚
  • How to organize myself. Yes, it may sound stupid, but you don’t know how organized are youย  until you have a chance like this.
  • How to sleep less than 4 hours and write (working) code :-). This drives us to an eternal discussion: tea or coffee? Tea works better for me…

The future…

In the future, I plan to finish the driver code, of course. Now, I’m personally commited with it. I should finish the driver’s code for the release of GDAL v1.7.0, and I’m going to work in this way. As I said, you can check the todo tasks, and the planned schedule (always under revision), in the project page.

Last, but not least, I’d like to thank my mentors, and all the GDAL and PostGIS development teams members for their patience, solving all my doubts. Of course, thanks to the OSGeo for giving me this chance of learning and helping the Open Source community.

Oh, and this is for Wolf Bergenheim: I think I escaped punishment of the Knights of Ni!, the keepers of the sacred words: Ni, Peng, and Neee-Wom (“Those who hear them seldom live to tell the tale!”). Will I have my T-Shirt? ๐Ÿ™‚ ๐Ÿ™‚ ๐Ÿ™‚

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2 Comments leave one →
  1. August 27, 2009 10:37 pm

    Nice job and very cool! I’ve been waiting to try this since June… I’m going to go through all the instructions this afternoon, as I’m trying to get gdal-1.6.2 built, load data and images into a postgresql database, and then try some stored procedures on the data. If I can help with testing, documentation, or code, I am more than willing.

  2. August 29, 2009 5:13 am

    Hi Jeff,

    Thanks for your comment. If you have any problem, I’ll try to help you ๐Ÿ™‚

    Best regards,
    Jorge

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