Re: [OpenMap Users] Floats Vs. Doubles

Hi Martin,

On Dec 3, 2003, at 11:55 AM, Martin Chapman wrote:

> Don,
>  
> Why did the architects of OpenMap choose to use floats versus doubles
> to store point data? 

It was a design decision made in 1996, and we chose to save memory over
the precision of 7-10 feet, or whatever precision the float gives. It
depends on the latitude, but I can't remember exactly what the number
is at the equator.

Most of the data sources we dealt with at that time were world-wide
databases, and the float accuracy was good enough.

> Sometimes I have a precision problem when plotting geometry on the map
> because my source data is double value and the coordinates get
> truncated.  This is a problem when dealing with high resolution
> satellite imagery that requires sub-meter accuracy, which is nine
> decimal places I think.  Do you know how many decimals a float can go
> to?  Is there a way to get around this problem?

Doesn't the number of decimal places depend on the number you are
trying to represent?

The only way I know to get more precision is to modify the Projection
libraries and OMGraphics to use doubles in addition to floats. Big
job.

- Don

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