Daniel Morissette wrote: > jerha202 wrote: >> When setting a rectangle covering 709 objects, it takes 11 seconds to >> loop through them. When using a rectangle covering 66 objects, it >> takes 8 seconds. Unfortunately, this is insufficient for our >> purposes. Does anyone else have experience of spatial query >> performance issues, particularly on Windows CE? Any ideas of what we >> could try to get better results? What should be the computational >> time complexity with regard to the number of objects in the rectangle >> and the total number of objects? >> > > That's an awful amount of time for such a small resultset. How much time > does the same query take on a PC? It should be only a fraction of a second.
Yes, I also agree it's very long. Just to give some comparison, in some of my tests, I read Shapefile with 3700 roads where each feature is returned as OGRFeature object with 52 (!) attributes. It takes 20-25 seconds to render the whole shapefile on 240x320px screen under Windows Mobile 5.0. No spatial index is utilised. > I not familiar with the limitations of the filesystem of a pocket PC, so > all I can say is that when a spatial filter is used, then the internal > R-tree spatial index is used to fetch the features of interest. This > could reault in lots of random disk access, i.e. multiple blocks of 512 > bytes being read from random locations in the file... if the pocket PC > OS is not efficient with fseek's in binary files then that could > possibly explain the poor performance. It should be efficient enough. However, there may be performance difference between accessing built-in flash memory and memory card. I'd suggest to try to read data from memory and from card and compare results. BTW, some time ago someone posted interesting, and weird at the same time, timing of I/O operations on Windows CE 4.x and 5.0: http://groups.google.pl/group/microsoft.public.windowsce.platbuilder/browse_thread/thread/33959bd4d220a83f/1 So, it's also a good idea to try both versions of Windows CE. Greetings -- Mateusz Loskot http://mateusz.loskot.net Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/mitab/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/mitab/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
