issue_comments: 379850842

On Apr 9 2018 11:43 AM, Ryan Abernathey wrote:

I really need to know what xarray can and is planning to do with tiff's so that I can not only use them but also document stuff for a dozen or more of my coworkers

@ebo, we are very glad to hear your input about how you might use xarray together with geotiff data. The majority of xarray developers are coming from a netCDF background, so this is somewhat new territory for us. It sounds like you have a real need for the computational tools that xarray provides. Engaging the geotiff community could potentially be very advantageous for xarray, since it could bring lots of new users. On the other hand, there are already lots of powerful tools in the geotiff space, and we have limited resources (i.e. time), so we need to be a bit conservative.

It would probably be useful to clarify how the decision making process works on things like this for open source projects. There is no xarray master plan that can provide a simple answer to your question of "what xarray is planning to do with tiffs". The main questions that have to be answered when deciding whether to add a big new feature are - Does this feature make sense within the "scope" of the project? (Can be difficult to answer--much discussion is usually required.) - Do the xarray developers have the time and expertise to implement and support such a feature?

The first item, regarding "scope," is being addressed now via this discussion. What are the pros and cons of attempting to add the new feature? Different people will have different opinions. Let's hear them out. A key question, as identified by @fmaussion, is whether the geotiff data model is compatible enough with the xarray data model enough to provide a full-featured writeable backend. In other words, can I write any arbitrary xarray dataset to geotiff and then read it back, with no loss of information. If the answer is "no," then it will be hard to convince the xarray community that geotiff is a suitable candidate for a backend.

If you feel strongly that we need the ability to not only directly read (as we can already with open_rasterio) but also directly write geotiff, you should lay out your arguments persuasively, taking into account not only the immediate impacts on your personal project but the impact on xarray as a whole. There may be good ways to achieve what you want without making any changes to xarray, i.e. by creating a small standalone package to transform geotiff to / from xarray (as in @Schlump's example); that option needs to be considered seriously.

The second item (time) is a rather strong constraint: xarray is a volunteer effort. There are currently 369 open issues in xarray. Which ones should be the top priority? Will attempting to add a new feature lead to much more work down the line, in the form of unforeseen bugs?

Ultimately, what happens in xarray is determined by the needs of the xarray developers themselves, who use xarray heavily in their daily science work. This may sound exclusive, but it is the opposite, because anyone can become an xarray developer. The reason we can read geotiffs today is because, one year ago, @fmaussion rolled up his sleeves and wrote the rasterio backend (#1260).

That little number 1260 is a link to a merged pull request (aka "PR"). A PR is much more powerful than a feature request; it is an actual implementation of the feature someone wishes to see in xarray. Anyone is free to make a PR to xarray, although before doing so, it is good to discuss the possible new feature via the issue tracker, as described in the xarray contributing guide. As a full time programmer in a lab dealing with geospatial data, you yourself are already a prime candidate to implement your desired feature! 😉

As an example of how a new backend was incorporated into xarray, you can refer to #1905, in which @barronh implemented a backend for "pseudo-netCDF" a file format used by his research group. Skimming through that discussion will give you a good idea of some of the questions that arise in implementing new backend functionality.

Apologies for the long digression into open-source politics. I thought it would be useful to clarify these things.

No need to apologize about a long digression into open-source politics, and I fully understand and smack in the middle of that with at least 4 different projects. I also know about issue/commit numbers on github/bitbucket/redmine/etc. NASA has formal rules about what can be released and when. My last open-source project took 9 months to get the software release authorized, but that was for an entire project new code. For basic image I/O support I would not expect any problems, but I have to get permission before releasing anything beyond snippets and examples that do not include primary workflows. I will release as much as I can back in the the public domain, but this starts to get complicated as the scope grows.

I do not remember seeing anyone use the acronym PR for "pull request" before, so sorry for that confusion. I just could not guess it in the context.

The argument for providing basic functionality for GeoTIFF's and geotiffs, is that it is a common dataset used along side NetCDF and HDF. I can, if you need me to, try to track down a stack of sites which provide images in GeoTIFF's such as NASA's Giovanni, Digital Globe, Planet Labs, just to name a couple off the top of my head. How many folks here work in and around GIS folks?

I will have to post back later (probably to several separate issues) to address several of the pointers raised above, but I have to get on to fleshing some of this out.