Specifying spatial types in test fixtures

[haxney]

Having looked at the documentation and code for a bit, I can't figure out a way to specify geometry types in Rails YAML fixtures. Is there a way to do this, either by specifying the attributes directly with something like

model:
  pos: !ruby/object:Point
    x: 1
    y: 1

or by using WKT like this:

model:
  pos: POINT(1 1)

If there isn't already a way to do this, consider this a feature request for such functionality. I would be willing to help write the necessary code if given some pointers.

[dazuma]

Okay, I'm going to have to think about how to do fixtures properly. In general, YAML serialization is fairly high on the to-do list right now.

I see that you also have a fixture-related issue open with spatial_adapter. Since you've clearly spent some time trying to figure out spatial fixtures, would you say spatial_adapter's syntax for geometry objects within a fixture is the way to go, or do you think a syntax closer to your WKT example would be preferable?

[haxney]

would you say spatial_adapter's syntax for geometry objects within a fixture is the way to go, or do you think a syntax closer to your WKT example would be preferable?

I think the spatial_adapter-style syntax would be better, especially for more complex geometries, like polygon. WKT is nice for points, but the YAML syntax for points can be as short as:

model:
  pos: !ruby/object:Point {x: 1, y: 2}

Which negates most of the advantages of using WKT.

In order for YAML to create Point objects, rather than hashes, you'll need to use YAML::add_domain_type or add_ruby_type to register a handler. I was able to get the WKT version semi-working using the following (in my spec_helper.rb):

YAML.add_domain_type("haxney.org,2011","point") { |type, val| RGeo::Geographic.simple_mercator_factory.parse_wkt(val) }

and then using it in a YAML file like so:

model:
   pos: !haxney.org,2011/point POINT(5 -5)

This works, but it doesn't seem like an ideal solution. One issue that didn't have a clear solution was the handling of factories. It seems like having a factory for each geometry type is inherent in the structure of RGeo, and so it wouldn't make sense to create a point (or other geometry) without a factory.

One solution is to take advantage of the fact that the second argument to YAML::add_domain_type ("point" in my example) can be a regex, and the type block argument contains whatever the user provides. This would allow for something like:

model:
  pos: !haxney.org,2011/simple_mercator:point POINT(5 -5)

where the value of type would be "simple_mercator:point", and the block passed to YAML::add_domain_type could use that to create a point with a simple mercator factory. If you wanted to get really fancy, you could try to have some way of cramming arbitrary Proj4 projection definitions in there, but just having a few static options (like simple_mercator, spherical, cartesian, etc.) would be enough to get by. Alternatively, you could have the factory be an attribute like:

model:
  pos: !ruby/object:Point
    x: 5
    y: -5
    factory: simple_mercator

which would make putting arbitrary projection information much cleaner.

[tetsutan]

Hi. I have known this bug, too. So, I wrote a patch to read WKT (but not enough). Is this not right way to fix the problem? (I have checked Point as WKT only)

https://gist.github.com/1093641

[januszm]

@haxney @tetsutan is this still an issue or should we close it?

[tetsutan]

No problem. Thanks.