ArcGIS geometry update from table XY

Question

I am trying to update the geometry of a point FC stored in a FileGeodatabase using ArcPy.

I got this Python script to compare the values of the SHAPE@X and SHAPE@Y and change the Geometry if not equal to the values stored in the attribute table (X_UTM_WGS84, Y_UTM_WGS84).

Even if I edit the feature and remove the extra digits past the second digit I get this when I print the values: I do not understand why the values are different ???

***** CODE USED:

2015-02-26_Compare_Geometry_With_Table_XY.py Compare the Geometry of points using the table values

import arcpy

fc = "D:/DATA_2014.gdb/UTM/TEST_PROJECTION_PT"
fields = ('SHAPE@X', 'SHAPE@Y', 'X_UTM_WGS84', 'Y_UTM_WGS84', 'POINT_NAME')

 Create search cursor for feature class 

i=0
with arcpy.da.SearchCursor(fc, fields) as cursor:
    for row in cursor:  # row[4]+ POINT NAME OUT OF PRINT
        i+=1
        print 'POINT ---> ' + str(i)
        print '\tSHAPE@X= ' + "%.11f" % round(row[0],11) + ' X_UTM_WGS84 = ' + "%.11f" % round(row[2],11) + ' EQUAL= ' + str(row[0] == row[2]) + ' DIFF= ' + str(row[0] -row[2])
        print '\tSHAPE@Y= ' + "%.11f" % round(row[1],11) + ' Y_UTM_WGS84 = ' + "%.11f" % round(row[3],11) + ' EQUAL= ' + str(row[1] == row[3]) + ' DIFF= ' + str(row[1] -row[3])

del cursor, row
print '\t\tEND....'

***** RESULTS:


POINT ---> 1
    SHAPE@X= 460965.17999999970 X_UTM_WGS84 = 460965.17999999970 EQUAL= True DIFF= 0.0
    SHAPE@Y= 1288230.55000000075 Y_UTM_WGS84 = 1288230.55000000005 EQUAL= False DIFF= 6.98491930962e-10
POINT ---> 2
    SHAPE@X= 413207.26999999955 X_UTM_WGS84 = 413207.26999999955 EQUAL= True DIFF= 0.0
    SHAPE@Y= 1382676.34999999963 Y_UTM_WGS84 = 1382676.34999999963 EQUAL= True DIFF= 0.0
POINT ---> 3
    SHAPE@X= 433224.66000000015 X_UTM_WGS84 = 433224.65999999997 EQUAL= False DIFF= 1.7462298274e-10
    SHAPE@Y= 1363812.55000000075 Y_UTM_WGS84 = 1363812.55000000005 EQUAL= False DIFF= 6.98491930962e-10
POINT ---> 4
    SHAPE@X= 428742.87000000011 X_UTM_WGS84 = 428742.87000000000 EQUAL= False DIFF= 1.16415321827e-10
    SHAPE@Y= 1233218.47000000067 Y_UTM_WGS84 = 1233218.46999999997 EQUAL= False DIFF= 6.98491930962e-10
POINT ---> 5
    SHAPE@X= 407040.38999999966 X_UTM_WGS84 = 407040.39000000001 EQUAL= False DIFF= -3.49245965481e-10
    SHAPE@Y= 1227264.44999999925 Y_UTM_WGS84 = 1227264.44999999995 EQUAL= False DIFF= -6.98491930962e-10
POINT ---> 6
    SHAPE@X= 403344.58999999985 X_UTM_WGS84 = 403344.59000000003 EQUAL= False DIFF= -1.7462298274e-10
    SHAPE@Y= 1250201.60999999940 Y_UTM_WGS84 = 1250201.61000000010 EQUAL= False DIFF= -6.98491930962e-10
POINT ---> 7
    SHAPE@X= 420615.79999999981 X_UTM_WGS84 = 420615.79999999981 EQUAL= True DIFF= 0.0
    SHAPE@Y= 1249885.83999999985 Y_UTM_WGS84 = 1249885.83999999985 EQUAL= True DIFF= 0.0
        END....

Answer 1

Those coordinate differences are measured in Angstroms.

File geodatabase uses a technique similar to the integer storage representation conversion in enterprise geodatabases (ArcSDE) to snap 64-bit floating-point coordinate values to a feature class coordinate resolution grid. This coordinate resolution is established at feature class creation (and it's usually on the order of millimeters, not 6 orders of magnitude smaller). Your feature class appears to have been created at centimeter (1.0e-02 m) resolution.

The differences you are seeing are artifacts of rounding at the far edge of mantissa storage in IEEE 64-bit floating-point representation. If you want to do floating-point value comparison, you need to be prepared to apply a "within" tolerance, or convert to integers at some scale factor (which is what FGDB is doing).