Hi Ben, Interesting approach, but only works if you know how you want to break things up ahead of time. I'd like to be able to pick a point and say 'give me everything within 1km' or 'give me everything within 100km'.
Cheers, Pete On Sep 9, 4:30 pm, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > Dave, > > Thank you for this post. Your description of how to handle date > ranges led me to a solution on the map lat/long issue that has gotten > so much discussion in various threads. I've posted the following in a > couple of other threads as well, since it seems to be a real issue. > But the solution is redundant properties, as you indicate. Basically, > the idea is finding a way to tokenize a region so that an infinite > number of points becomes a block... > > What I do is that I break down the grid into sub-degree squares by > truncating after the first decimal point, and then when I save > something that I need to find on the map later, I save metadata with > that point indicating the surrounding grid squares. > > So if I have a point with long -122.123123123 and lat 35.56565, that's > in a grid square called -122.1x35.5, and it's surrounded as follows: > > [-122.2x35.6][-122.1x35.6][-122.0x35.6] > [-122.2x35.5][-122.1x35.5][-122.0x35.5] > [-122.2x35.4][-122.1x35.4][-122.0x35.4] > > Those are all represented in my object as a list > (db.StringListProperty, so you have to do the right permutations to > make them into strings), and because of the way lists work, if a point > that you're searching on is in any of the grid squares associated with > a saved point, that saved point will come up. > > To wit, if you have saved that above point, and someone comes in > searching on an address that corresponds to: > > LONG -122.0857 > LAT 35.69999 > > that corresponds to grid square '-122.0x35.6', which is in your upper > right hand corner. Thus, if your code is something like... > > square = '-122.0x35.6' # based on whatever normalizing function > you use > points = (SELECT * FROM Locations WHERE gridList=:1", square) > > ...you'll find that the original point we saved above will return. Of > course, this is a simple example. Each grid square can be any size > and shape, and you can cluster as many as you like in whatever shape > you like. For me, a 3x3 grid of 0.1 degree squares is good enough. > 0.1 degrees is approximately 7 miles in the north/south direction, and > up to that big in the east-west dimension, at least at the equator. > It's a blunt tool, but once I've got a reasonable set of map data > back, then I can do further operations to throw out what I don't need. > > It's all about metadata. Don't think in terms of inequalities and > boundary conditions, think in terms of inclusive ranges. With a > little creativity, you don't need inequalities, at least for this > problem. > > Best, > > Ben > > On Sep 7, 7:37 am, "David Symonds" <[EMAIL PROTECTED]> wrote: > > > On Sun, Sep 7, 2008 at 9:42 PM, Nash <[EMAIL PROTECTED]> wrote: > > > > This is the part of the appengine that starts to get frustrating, the > > > more criteria you will want to add, the more impossible you will find > > > it to be. > > > If all you are looking for is to find data for a particular date then > > > I suggest adding three fields to your entity: year, month, day. If you > > > want to get results for a particular day, just provide values for > > > these attributes. By breaking the date unto three parts, you can also > > > get results by month, by year etc. But if you have want to pull data > > > between two points and between two dates, then good luck! > > > In that case, you would use multiple properties: one for the whole > > date, and then split it out Y/M/D. Remember: BigTable is designed for > > lots of redundant data that makes it really easy and fast to index and > > find what you want. Don't be afraid to drop in redundant properties. > > > Dave. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~----------~----~----~----~------~----~------~--~---
