The documentation examples and the "demo gallery" are worth a look: http://code.google.com/apis/maps/documentation/javascript/examples/index.html http://code.google.com/apis/maps/documentation/javascript/demogallery.html
The gallery includes this polygon drawing demo: http://www.the-di-lab.com/polygon/ It's very simple but might be a good starting point. Cheers Ben On Mon, May 16, 2011 at 2:35 AM, Richard Quadling <rquadl...@gmail.com>wrote: > Your explanation is excellent. Thank you very much. > > Do you know of any tools that provide a user with polygon drawing? > Something I don't want to have to start from scratch? > > A library of useful apps that have been generated using the maps API > would be excellent. > > On 14 May 2011 03:30, Ben Appleton <apple...@google.com> wrote: > > > > > > On Fri, May 13, 2011 at 9:09 PM, Richard Quadling <rquadl...@gmail.com> > > wrote: > >> > >> On 12 May 2011 21:41, Ben Appleton <apple...@google.com> wrote: > >> > > >> > On May 13, 2011 2:37 AM, "Richard Quadling" <rquadl...@gmail.com> > wrote: > >> >> > >> >> On 12 May 2011 14:12, Ben Appleton <apple...@google.com> wrote: > >> >> > It sounds like you have a polygon containment forest: a collection > of > >> >> > rooted > >> >> > trees whose roots are outer polygons, children are polygonal holes, > >> >> > grand-children are polygonal islands inside holes, etc. You can > >> >> > certainly > >> >> > represent containment in JavaScript, but it's not necessary for > >> >> > rendering. > >> >> > Therefore the Google Maps API does not represent containment. > >> >> > > >> >> > There is an unfortunate caveat. Many browsers use Canvas to render > >> >> > vector > >> >> > graphics, and Canvas requires that outer vs inner polygons have > >> >> > opposite > >> >> > orientations - it implements only "zero-winding fill". For example, > >> >> > if > >> >> > your > >> >> > outer boundary is clockwise, your holes must be counter-clockwise, > >> >> > islands > >> >> > within holes must be clockwise, and so on. If you need to determine > >> >> > the > >> >> > orientation of a polygon you can use the geometry library's > >> >> > computeSignedArea method > >> >> > > >> >> > > >> >> > ( > http://code.google.com/apis/maps/documentation/javascript/reference.html#spherical > ). > >> >> > You can then traverse your containment tree to ensure that outer vs > >> >> > inner > >> >> > polygons have opposite sign, reversing polygonal loops to negate > >> >> > their > >> >> > sign > >> >> > where necessary. > >> >> > > >> >> > Incidentally the geometry library also has a method to encode > >> >> > polylines/polygons in the same format as you reference, but > compiled > >> >> > so > >> >> > it > >> >> > loads faster. > >> >> > > >> >> > So I suggest: use google.maps.Polygon to visualize your polygons, > but > >> >> > wrap > >> >> > it in another class or datastructure to represent your containment > >> >> > forest. > >> >> > To visualize simply add the google.maps.Polygon to the map. When > >> >> > constructing queries to your server, consult your wrapper class / > >> >> > datastructure to determine which polygonal loops are outside vs > >> >> > inside. > >> >> > Optionally, also switch to using the compiled poly encoder in the > >> >> > geometry > >> >> > library. > >> >> > > >> >> > Hope that helps > >> >> > Ben > >> >> > > >> >> > >> >> Thanks for that. > >> >> > >> >> encodePath only allows for a single path, not a set of paths. I'm > >> >> simply concatenating them with | (pipe). And splitting and decoding > >> >> them in PHP. How do I access the compiled encoder. I'm currently > >> >> using google.maps.geometry.encoding.encodePath() > >> > > >> > Oh great, you're already using it. I thought you meant you were using > an > >> > older JavaScript poly encoder that had not been compiled. > >> > > >> >> Very useful. -ve values from computeSignedArea() relate to the outer > >> >> polygons and +ve values to the inner ones. > >> > > >> > That's right. > >> > > >> >> I think the final piece for me now is to determine from 2 polygons if > >> >> one is completely within the other. > >> > > >> > I thought you already had this structure. Else, how are you currently > >> > generating KML and WKT queries as you mention? > >> > > >> > Cheers > >> > Ben > >> > > >> > >> I'm still in building/designing/learning/playing phase of the > >> development. Essentially proving to myself and the team that what we > >> want to do is possible. I'm working things out manually. > >> > >> In the last test (test 5) I create a map, added a simple polygon and > >> send the encoded path to PHP to decode and turn into WTK for SQL to > >> get the pins to pass back to the map for displaying. > >> > >> For a single polygon (I've used 2 sliders to allow different number of > >> points and radius) this is working fine. I have to use a polygon as > >> whilst I'm only playing with regular ones, the final view of the app > >> will be to have complex boundaries. > >> > >> The next test was to add the exclusion polygon. That's where I'm at > >> now. Though I'm still playing I know that the users will need to be > >> able to define these complex areas. > >> > >> > >> The purpose of the tool is to allow our call centre staff to display > >> the location of a LGV (Large Goods Vehicle) breakdown and, based upon > >> the contract (essentially who owns or is hiring the vehicle) provide a > >> ranking of the most appropriate maintenance engineers, nearest to the > >> breakdown. We have nearly 1,000 service depots in the UK. Each depot > >> covers an area. Sometimes just as a 30 mile radius, others cover a > >> specific county, or part of it. Others don't go inside a circular > >> motorway/ring road, etc. All different. Some will travel over > >> bridges/ferries/etc. Or have any sort of boundary/exclusion. > > > > OK - so for this first step, you only need to display a complex polygon > > (such as a polygon with multiple inner and outer boundaries). That should > > work fine, so long as exterior vs interior loops wind in opposite > > directions. > > > >> > >> The next step in the design is to allow a backoffice user the ability > >> to plot out these boundaries. The boundaries will be stored in our SQL > >> Server in 2 ways: > >> > >> 1 - Using the Google Maps encoded form, so when I need to display the > >> polygon, I can just supply that to the client app, call the decoder > >> and add each path to the polygon. > > > > So long as your exterior and interior loops wind in opposite directions, > I > > believe you can store a google.maps.Polygon as a pipe-separated sequence > of > > encoded LatLng strings. > >> > >> 2 - As a SQL Server Geography type, so I can use SQL Server to do all > >> the intersection and find a list of service providers who cover the > >> point of the breakdown and are attributable to the contract for the > >> vehicle. > > > > For both of these cases you need to distinguish exterior vs interior > loops. > > In addition, if I understand correctly, for the SQL Server Geography type > > you need to represent the polygon containment forest I mentioned earlier > - > > that is, which polygonal loops contain which other polygonal loops. So > when > > a backoffice user plots out a boundary, either the UI itself or a > > post-processing step must construct the polygon containment forest. > > The UI could enforce this, by providing a flow where a backoffice user > adds > > a "child loop" to an existing loop - to punch a hole in an exterior loop, > > for example. Or you could compute this after the fact by testing which > loops > > lie inside which other loops. For non-intersecting loops, loop A contains > > loop B if and only if the first vertex of loop B lies inside loop A. So > long > > as there are only a handful of loops per polygon this should be fast > enough, > > otherwise you could use a faster (but more complex) scan-line algorithm. > >> > >> Obviously, there is more to the front end than just the map, but the > >> map is one of the key players. The map will also show any service > >> provider that has part of their boundary within the viewport, so, if > >> the preferred providers are unable to handle the breakdown (some > >> providers are quite small and only have 2 or 3 maintenance staff), the > >> user can see that there are other providers in the area who are linked > >> to the contract and may be able to help, even though it is outside of > >> their boundary. It's all very fluid, but not a total free for all. > >> Travelling time for the maintenance people means some driver is > >> sitting in their cab waiting and having the stock not being delivered. > >> The vast majority of the contracts are delivering perishables and > >> delivery times are quite tight. > >> > >> And I then, on top of all of this, ... > >> > >> GoogleMaps ... > >> > >> LatLng(latitude, longiture) > >> Polygon orientation of points to create a small closed area : clockwise > >> > >> WTK (as used by SQL Server) > >> POINT(Longitude, Latitude) <<< Reverse > >> POLYGON orientation of points to create a small closed area : > >> anticlockwise. Otherwise the enclosed area encompasses the whole of > >> the earth, except the small part "outside" the boundary. > >> > >> And to this, the MS SQL native Geography::Point() method uses > >> Point(latitude, longitude), the reverse of WTK but matches Google Maps > >> API. > >> > >> Don't you just love standards! > > > > Haha, I'm sorry for you. Lat/lng versus lng/lat seems to be a perennial > > source of pain in GIS systems. > > Cheers > > Ben > > > >> > >> -- > >> Richard Quadling > >> Twitter : EE : Zend > >> @RQuadling : e-e.com/M_248814.html : bit.ly/9O8vFY > >> > >> -- > >> You received this message because you are subscribed to the Google > Groups > >> "Google Maps JavaScript API v3" group. > >> To post to this group, send email to > >> google-maps-js-api-v3@googlegroups.com. > >> To unsubscribe from this group, send email to > >> google-maps-js-api-v3+unsubscr...@googlegroups.com. > >> For more options, visit this group at > >> http://groups.google.com/group/google-maps-js-api-v3?hl=en. > >> > > > > -- > > You received this message because you are subscribed to the Google Groups > > "Google Maps JavaScript API v3" group. > > To post to this group, send email to > google-maps-js-api-v3@googlegroups.com. > > To unsubscribe from this group, send email to > > google-maps-js-api-v3+unsubscr...@googlegroups.com. > > For more options, visit this group at > > http://groups.google.com/group/google-maps-js-api-v3?hl=en. > > > > > > -- > Richard Quadling > Twitter : EE : Zend > @RQuadling : e-e.com/M_248814.html : bit.ly/9O8vFY > > -- > You received this message because you are subscribed to the Google Groups > "Google Maps JavaScript API v3" group. > To post to this group, send email to > google-maps-js-api-v3@googlegroups.com. > To unsubscribe from this group, send email to > google-maps-js-api-v3+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/google-maps-js-api-v3?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Google Maps JavaScript API v3" group. To post to this group, send email to google-maps-js-api-v3@googlegroups.com. To unsubscribe from this group, send email to google-maps-js-api-v3+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-maps-js-api-v3?hl=en.
