Althought the Nyquist theorem isn't implemented (I'll have to think of this one, a bit tricky since one would have to implement a low pass filter after going thru a Fourier series on polylines segments groups, then back to regenerate spatial information ... hummm, not really a work for dear old Mapbasic ...), you may try Topocheck from the MI List FTP site (look at top downloads ( ... ;) forgive me, it's soooo good for my little ego...)), that'll enable you to filter by a combination on two parameters : minimum distance between points, and maximum / minimum angle between segments. One drawback ... it's french, but straight forward (well ....better back up your table first). BTW, I'll put an english version on my site, and the list as soon as I'll find someone with a Mapbasic compiler to recompile the english version .... (I'm afraid I gave up MapInfo devs a few years ago, too tired by local MI reseller - kindof having the 'new version' of MI 6 to 10 month too late (when there was already a new version in the US ...), and very, very, very bad partners support (I mean even worse than none !). But that's another rant.) I think other tools on the listFTP site will allow you to use a corridor based simplification. Eric Maranne EMI Informatiques web : www.cycweb.com/equipage ~~~~~~~~~~~~~~~~~~~~ (33) +4 42 06 22 22 GMT +1 [EMAIL PROTECTED] ~~~~~~~~~~~~~~~~~~~~ GIS - VRML Integration > -----Message d'origine----- > De: andre boessenkool [SMTP:[EMAIL PROTECTED]] > Date: jeudi 18 mai 2000 11:30 > A: [EMAIL PROTECTED] > Objet: MI: Data reduction > > G'd day all, > > For my mapping work I use very detailed polyline and contour data (amongst others), which have been produced from 1:50,000 scale maps through digitizing. The line data are extremely finely sampled and hence reproduce beautifully all curved portions of lines at that scale. However, the ultimate scale at which my maps will be produced is 1:200,000 or 1:400,000, a linear reduction of 1 in 4 or even 1 in 8 and the precision of the original data is therefore way too high for the end product. > > Question is: Is anyone aware of a routine through which one can pass the data files, and which will reduce the data density in such a way that at the smaller scale the exactness is still maintained. There is a mathematical rule which says that the spatial sampling frequency is dictated by the 'curviness' of the sampled line in order to restore the original curve without aliasing. (The word Nyquist frequency comes to mind). > > Anyone has any thoughts on this?? > > TIA > andre > > > > from: andre boessenkool > po box 101 - vlottenburg 7604 > south africa > tel (+27 21) 881 3188 > fax (+27 21) 881 3189 > [EMAIL PROTECTED] > > > --- > Incoming mail is certified Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.146 / Virus Database: 70 - Release Date: 09/05/00 > << Fichier: ATT00002.htm>> --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.146 / Virus Database: 70 - Release Date: 09/05/00 ---------------------------------------------------------------------- To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
