Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>This shows the algorithm for encoding: <a href="http://code.google.com/apis/maps/documentation/utilities/polylinealgorithm.html">http://code.google.com/apis/maps/documentation/utilities/polylinealgorithm.html</a></p> <p>A decoder is available from Prof Mark McClure at <a href="http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/decode.html">http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/decode.html</a></p> <p>Encoding uses offsets (deltas) from point to point. The offset of the first point is calculated from (0,0) so it equals the coordinates of the first point. The second point is encoded as the offset of point two from point one, and so on.</p> <p>To join two lines, you first need to find the last point of the first line, and the first point of the second line.</p> <p>Then, you calculate the offset of line two from the last point of line one, and substitute that offset for the first coordinate in the second line. Thus the second line does not start with an offset from (0,0), but an offset from the end of the first line.</p> <p>Now, the last point of the first line will need to be re-encoded to show that there is more to follow. </p> <p>Because each encoded point in each line can consist of a variable number of characters, it's not easy to find any point (even the first) without decoding the entire line.</p> <p>So: to do the work you will need to do some decoding and recoding. It's probably easiest to decode each line into an array of points and then re-encode the whole thing. Encoding is quick and easy in PHP -- see McClure's site again.</p> <p><em>This contradicts an answer given by me in the Google Maps Version 2 Group where I wrongly assumed the length of each encoded point to be strictly five characters.</em></p>
    singulars
    1. This table or related slice is empty.
    1. POMerging multiple encoded polylines into one encoded polyline
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USAndrew Leach
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COAndrew, Thanks for the info! That definitely helps me understand how it all works. Due to the amount of coordinate pairs that we're going to be working with, reencoding the whole polyline would take too long and too many resources. Since I'm also producing the appending polyline, I have the coordinate pairs. What if I were to encode just the first pair coords from 0,0 and from the last point on the existing polyline and subbed them out? Would something like that work?
      singulars
      1. PO
      1. USDan Mandle
    2. COIn order to re-encode the last point in the line you will also need to know the previous point to work out the offset. What is "taking too long"? I have to process around 7500 points for a map of [Lundy Island](http://www.achurchnearyou.com/parishfinder.php?lundy) which takes six seconds using MySQL and PHP: but that also includes finding that polygon in the first place (point-in-polygon analysis) together with a bit of other data too. Less complex shapes are a **lot** quicker! [That's a V2 map, but we're talking about server-side processing]
      singulars
      1. PO
      1. USAndrew Leach
    3. COGreat answer, Andrew. Dan, for 7K points, I'd just decode, append and re-encode. As you said, it only takes a few seconds. If you were talking about millions of points or doing this on-the-fly, I'd go with Andrew's approach, OR just send down two separate encoded polylines to the client. It will only be a few bytes more.
      singulars
      1. PO
      1. USChris Broadfoot
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload