Sean,
Would the defaults result in overly large attribute files? By a small amount or an excessive amount? Or would the defaults result in truncation of values?
For shapefile the default is width=24,precision=15,so this means 24 bytes for every floating point number. In theory a number couldn't have a magnitude larger than 10^(24-15-1), but the shapefile driver will remove decimal figures if that's needed to preserve the integer part. But if a number is larger than 10^24, its last digits will just be truncated with a warning (there's no good solution here. I kind of remember of past discussions if we shouldn't fallback to scientific notation, but we didn't implement that). In that situation, the user would have to increase the width (one can question the appropriateness of using Shapefile .dbf for numbers of very large magnitude). So basically the default should be fine (as far as preserving information is concerned) for most common ranges of floating point numbers, but will misbehave for very large ones. Obviously for people storing small numbers with few decimals, 24 might be felt as excessive.
For MapInfo I was actually partially incorrect. It has indeed a mode of fixed precision, but if you don't specify the width, it uses IEEE754 double precision for .tab, et a non-fixed width text representation for .mif.
Shapefiles are (probably) the only format OGR handles on the writing side that require, explicit or implict, width.precision (PostGIS or other databases are similar to MapInfo and support both fixed width/precision and floating-point)
Even -- http://www.spatialys.com My software is free, but my time generally not. _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/gdal-dev
