Hi Bob! I see that mistakes appear at 4th position after dot, so I need such an accuracy. My project demands great accuracy - it should create a road map for solving traffic problem and error in 0,1 mm brings me to wrong result - no way between roads. I can work _only_ with MapX - such are system requirements and se� no way to set table bounds while creating. I'll try to search better. As far as I see my map's bounds are up to 100km, I work with St Petersburg and I guess 200 km are enough
Hi Kat If you need accuracy to one tenth of a millimetre then your bounds can only be 200 km wide and 200 km high. I do not know where you are in the world but 200 km is quite small. The bounds are effectively stored in the table at creation time ( as stated before the bounds are 2,000,000,000,000 times the step size stored in the MAP file ). The coordsys clauses set the unit of measurement and projection parameters at display time. All this can be done in double precision and so bounds are not really relevant at display time. The important time is when your table is created. How are you doing this ? Are you using MapInfo or MapX to create the table? Make sure you add the bounds clause at creation time and use 200km square if you need 1/10th mm accuracy, 20 km square if you need 1/100th etc. If you need 1/10th mm and greater than 200 km then MapInfo can not do this! You would need a system that stores double precision like AutoCAD or ESRI shape format. The advantage of the MapInfo method is the size of the files and that before maths co-processors were standard some of the computations could be done using integer arithmetic which would be faster. What is your application that you need 1/10th mm accuracy though? Regards Bob In message <[EMAIL PROTECTED]>, Katrin writes > >Thanks to all. Now I' ll be trying again and again two of the variants. > >But I haven't heard yet the answer to another question - precision, is there a >number position that is insignificant. Phrase "If those coord are meters, you >want a precision to the tenth of a millimeter" looks like this, but I have >coordinates in meters and error appears in 0.0001m = 0.1 mm. > >And how could I change coordsys in MapX except NumericCoordsys and >DisplayCoordsys. These bounds do not change a table, available only at runtime. > > > >Hi Kat > >MapInfo stores coordinates as a whole number ( 4 byte integer ) times a >step size ( 8 byte double precision ). > >The X step size is ( Max X - Min X ) / 2,000,000,000 > >The Y step size is ( Max Y - Min Y ) / 2,000,000,000 > > >It therefore does not follow that smaller bounds mean more accuracy. If >all your coordinates are in exact multiples of 1 mm it is better to have >a step size of 1 mm than say 0.75 mm. With 0.75 mm units would fall at >0.75, 1.5, 2.25, 3 so 2mm could not be represented whereas it could with >1 mm step. > >To set an exact step size make your bounds 2,000,000,000 times the step >size you want. > >For the UK we set our bounds to 2000 km which gives us a step size of >exactly 1 mm. As Ordnance Survey give out coordinates for MasterMap to >the mm this means we can store and retrieve coordinates "Spot on". > >Regards > > >Bob >mapsbydesign.co.uk > > > >Best Regards, >Katerinka > >--------------------------------- >Do you Yahoo!? >Free Pop-Up Blocker - Get it now -- bob young Best Regards, Katerinka --------------------------------- Do you Yahoo!? Free Pop-Up Blocker - Get it now
