One Type, Two Types...

re: One Type, Two Types...

Martin Davis — Tue, 29 May 2007 19:40:25 GMT

The idea of using a bounding circle for geodetic objects is interesting. Presumably this is physically represented as a geographic location with a radius value? How do you compute this efficiently (e.g. do you actually compute the Smallest Enclosing Circle, or do you just pick an obvious point such as the centroid).

And then the big question: how do you index these circular envelopes? All the spatial indexes I'm familiar with use rectangles as their indexable item. Is there an index which handles circles directly?

re: One Type, Two Types...

SharpGIS — Tue, 29 May 2007 19:58:52 GMT

Ok, I buy why you need two different types, but please someone at least bring out the naming police here. You can't seriously consider naming it "Geography" ? Should that really prevent confusion?

"geography" (Noun): The study of the physical structure and inhabitants of the Earth.

"geometry" (countable and uncountable; plural geometries)

1. The branch of mathematics dealing with spatial relationships.

2. A type of geometry with particular properties.

spherical geometry

3. The spatial attributes of an object, etc.

What about "Geographic" ? At least this relates to the type of coordinate system that is uses, or even better "Spheric" so it doesn't necessarily relate to Mother Earth.

re: One Type, Two Types...

isaac — Tue, 29 May 2007 20:45:59 GMT

Ah, the naming issue... :)

From http://webster.com/dictionary/geography :

2 : the geographic features of an area

This seems reasonable to me, and feels better than "geographic", which is an adjective.

To be honest, our main concern with the name "geography" is that it sounds too close to "geometry".

re: One Type, Two Types...

SharpGIS — Tue, 29 May 2007 23:15:40 GMT

My point exactly. The geography is the FEATURES of an area, but not the AREA itself. You can view it as the other columns in a datarow that describes certain characteristics relating to the geometric shape.

In the sense you want it to be understood, the geometry type would also be 'geography'.

Since the datatype is describing the type of the data, it only makes sense that it is an adjective. It tells you that this is data described in a spherical space. Inconsistently the 'geometry' on the other hand doesn't tell you anything about the type of coordinate space.

Isn't 'Integer' considered an adjective too?

re: One Type, Two Types...

isaac — Wed, 30 May 2007 03:56:22 GMT

I'm sorry---I misread your comment.

I'm no grammarian, but in general, we name types after nouns, not adjectives. "Integer", for example, is a noun, and "integral" is the matching adjective.

For "geometry", I think we want definition 2 b : surface shape.

The same goes for most types in SQL Server: "char" (short for character---the adjective definition of which seems a bit odd for our use), "money" (not monetary), "timestamp", etc.

It's true that some are a bit odd in normal english usage---none of the dictionary definitions of "float" make sense here---but they're all used as nouns when we use them. (E.g., "Pass a float to the function.")

Cheers,

-Isaac

re: One Type, Two Types...

isaac — Thu, 31 May 2007 02:12:58 GMT

Martin,

You nailed it: picking a minimal bounding circle is tough, so we take the centroid and the smallest radius we can. I'll cover this more in a future post, but we don't actually use the MBR (or MBC) for indexing.

Cheers,

-Isaac

re: One Type, Two Types...

Tim McCurdy — Mon, 04 Jun 2007 01:32:08 GMT

I'm a novice at GIS, but I love it so. My comment on naming is this. When coding (TSQL or .NET), I'm usually using variables called "Area" when it refers to geometric shapes. It makes it more generic if I ever change that data type from say a Rectangle to a Region. To me, everything is area whether its a Polygon, Rectangle, etc. Also, "Shape" makes sense but it always takes me back to the days of the VB6 Shape control.

Cheers

In or Out?

Isaac @ MSDN — Mon, 29 Oct 2007 23:59:46 GMT

I've been stalling, trying not to say too much about spatial until it's actually available. The code

re: One Type, Two Types...

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Isaac @ MSDN : One Type, Two Types...

Weddings — Thu, 05 Jun 2008 13:37:30 GMT

This is a little bit less of an introductory post than the last one , but there was quite a bit of discussion about our decision to split our spatial types in two---one for our planar ("flat-Earth") model and one for our ellipsoidal ("round-Earth")