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OpenAerialMap

About The Project

OpenAerialMap seeks to act as a steward for the discovery and use of open aerial imagery. By bringing together a community of interested persons and providing a limited set of tools and expertise around them, OpenAerialMap seeks to help solve the problems of persons who need imagery that is not available through any other means.

OpenAerialMap is an idea that has been bounced around in many circles for a long time. The idea of an open source of aerial imagery is one that is not a new concept, and one that people in the Open Source Geospatial community have been working around.

There are many people who have actively expressed interest in the OAM project, with many different approaches. By taking a simple approach to the problem, we hope to encourage and allow all of these types of activity in the OAM community.

The Approach

The OAM ‘problem’, as it has been described so far, has oftentimes been bunched with a bunch of other problems. For the purpose of this attempt, we are going to deliberately and explicitly separate out the various aspects of the problem.

The key to this approach is to make each step of the process as simple as possible; that way, there is very little that can’t be replicated or replaced easily, and there are no complex moving parts that require significant maintenance.

The key parts of such an infrastructure are:

  • Imagery Index – a readily accessible way of finding information about imagery that is available and how to access it.
  • Storage – A distributed set of resources through which imagery can be made available for access by OAM tools.
  • Access Tools – Tools which use the Index and access data from Storage to build output that users of the OAM data will want. This includes everything from a WMS to a set of tiles that can be made available offline.

In order to support these mechanisms – and to keep them separate – there is no association between the Storage and the Index. The OAM project does not need to provide storage – instead, we simply document a way for users to publish their imagery, and document how to list such imagery in a publicly accessible index.

Imagery Index

The imagery index is a list of available imagery. It is designed to be simple. The primary object that the Catalog focuses on is Images. An image consists of a URL and some metadata designed to make filtering and accessing the imagery possible. It will also include a ‘cache’ of information determined directly from the imagery that is designed to make it easier for tools to use the imagery without necessarily requesting it – for example, image size in pixels. (This can be combined with the bounds of the image to generate a resolution, or level of detail, for the image.)

In addition to acting as an index of images that are prepped for OAM, OAM can act as storage for ‘archived’ images – image information that is available, but not processed for access through OAM. (These images can then be processed by interested parties and made accessible as usable images.)

You’ll note that the image objects are associated with a URL. This is deliberate – and a big part of the difference between the OAM of the future and the OAM of the past. Rather than being tied to a single centralized server, the OAM catalog is an index of data hosted elsewhere – allowing that piece of the puzzle to be easily swapped out for any other.

For more information on the existing work on the Imagery Index, visit Imagery Index.

Storage

In order to make OAM practical, data needs to be stored in a way that it is easy for tools which are using OAM to access it. What this means, in practice, is that there is a need to make imagery available from a machine where the network access is not such that the host of the imagery needs to pay a high margin on additional requests or bandwidth.

In the beginning, we expect that many large datasets will not be immediately available in OAM: instead, we expect that as the imagery is needed, organizations will need to find solutions to make their imagery available in a prepared way for access by OAM consumers.

Naturally, there are many more imagery providers out there who are able to provide imagery, but can not provide access to these images in a prepared form on the web for a number of reasons. We hope to work with these imagery providers to help them find a home for their imagery that fits their needs – whether that is solved by joining forces with other organizations like the Internet Archive, or working with universities to find homes for that data.

One of the primary conditions of the ‘storage’ layer of OAM is that the imagery must be accessible directly, and without significant limit. The expectation is that tools which need the imagery can work directly against it to create products or output.

At some point, the storage layer of OAM may evolve into access to some form of distributed storage; but the underlying means of storing the data is unimportant to the overall project. Instead, what is important is that the data can be accessible via a URL. Once you can make data available from a URL, you can change the underlying mechanism in any way you want.

In order to help move data into the storage layer, part of the OAM project will be determining the best way to store imagery for ideal access by tools. For local disk access, compression oftentimes slows your usage. However, for network imagery, this is not the case, and as such, a different set of defaults will need to be built and optimized as the project grows.

The concept behind the storage layer is:

  • Use simple, existing technologies
  • Search out friendly patrons in the short term, and investigate more complete solutions in the long term
  • Treat the URL/HTTP access as the primary way to find information, and don’t tie storage to any aspect of the catalog directly.

For more information on the existing work on Storage, visit Storage.

Access Tools

One of the key problems in the past with OAM has been that with so many different expectations for it, it has been difficult to reconcile those expectations in a way that meets a majority of them without overly complicating the project.

If you think of OpenAerialMap as a URL to access a tiled view of the world, you will find people who will be unable to use it, because what they really care about is hyperspectral imagery. If you consider OpenAerialMap to be a source of imagery used to help generate more accurate reports, you may similarly find yourself in competition for resources with people who need access in a WMS instead of direct access to data.

After careful consideration, it seems that the best approach to this problem is to take after the OpenStreetMap project: Rather than having all of these various competing needs be met by the OAM server, concentrate instead on creating an index of the imagery of the world which is as complete as possible, and allow the tools around that to flourish.

OpenStreetMap is an extremely active project for development; in fact, according to Ohloh, “This is one of the largest open-source teams in the world, and is in the top 2% of all project teams on Ohloh.” This success stems in large part from encouraging anyone working on code related to the OpenStreetMap project to contribute that code directly to the project’s SVN, centralizing developer knowledge and creating an extremely effective shared community.

The OpenStreetMap.org website is a very small portion of the development effort: although this is the primary host of the data, everything from Mapnik-based rendering to many successful editors to tool for analyzing and mass-updates of the data are maintained in the OpenStreetMap source code repository.

Our hope with the OAM project is to approach a similar level of transparency and shared development community by creating a community which is interested in using the OAM Catalog API and shared understanding of how to make imagery available, and building tools around it.

In this way, you can imagine someone building a tool which could refer to the OAM Index and build a tile set for distribution to remote users. You can imagine someone building a tool which allows a user to simply take a single snapshot of an area by selecting the imagery that best met their needs.

At the same time, you could have someone who wrote a tool to download a set of imagery and put it on a hard drive to ship into a crisis zone, as was done during the Haiti crisis, to make the source imagery available for deeper analysis in GIS tools. You can imagine someone building a tool to create a single, large mosaic – or make that mosaic available as a WMS.

In all of these cases, we would encourage users to work with the community to contribute their applications to a centralized home in the OAM project, centralizing knowledge and effort.

The key, however, is that this software would then not be maintained directly by the OAM project in most cases. Other than the Imagery Index, the project would work to find ways for interested parties to hook up with resources to host their applications; however, the core of the project would be around maintaining and improving the imagery index.

For more information on Access Tools, visit Access Tools.