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FAQ: Why are LAYER tag values rounded in the ArcXML Programmer's Reference Guide?

Question

Why are LAYER tag values rounded in the ArcXML Programmer's Reference Guide?

Answer

The ArcXML Programmer's Reference Guide rounds some values in the NOTES section of the LAYER tag. This guide can be located at one of two places:

1. Page 341-342 of \ArcIMS3.1\Documentation\ArcXMLGuide3.1.pdf.

or

2. Through an Internet browser by clicking on Start > Programs > ESRI > ArcIMS 3.1 > Documentation > ArcXML Guide.
The following is a list of actual values used internally by ArcIMS:

A) Meters in an inch = 1/39.37 to the extent of a double-precision float, or
0.0254000508001016.

B) Calculating pixel size = Double-precision floats.

C) Relative scale values:

All internal calculations are done in double precision, and the number is rounded off to the nearest integer (or Long).

D) Feet in a meter = 12 * (1/39.37) in double precision, or 0.304800609601219.

E) Earth's circumference = 40,030.174 meters.

F) Meters to degrees = Multiply meters by 0.000008993220293.

G) Degrees to meters =

'an "l" or a "d" on variables for Long
'and Double, respectively.
'dPI is 3.14159265358979, as a double
lNumHalfCircles = (dDegrees / 180)
dRemainder = dDegrees - (lNumHalfCircles * 180)
L = ((dRemainder* dPI) / 180) / 2 'Deg2Rad / 2
dSL = sin(L)
dCL = cos(L)
dDistanceInMeters = (20015077.0 * lNumHalfCircles) + _
(12741994.0 * atan(sqrt((dSL*dSL)/(dCL*dCL))))