topic Re: Duplicated decimal coordinate values? in Data Management Questions

Duplicated decimal coordinate values?

ERIASGroup — Wed, 10 Jan 2018 05:59:53 GMT

Hello. I hope someone can help me with what appears to be an odd problem.

In ArcMap Desktop v10.5.1 I have calculated EN coordinates for a set of sample points for field work. However, I noticed that the coordinate values all have the same decimal values regardless of where they are located. The points are not located in a line so how can they have the same decimal values? For example, two completely separate point locations some 60 metres apart have the following values: P1 is E 315722.4077 / N 5809888.1804, P2 is E 315767.4077 / N 5809843.1804.

Please see attached image.

ALL the points have these same repeated decimal values. The field type is Double and precision is set to 6 decimal places. The data frame is correct with all project data in GDA_1994_MGA_Zone_55.

The same points calculated using DMS have unique values and are NOT duplicated at the seconds (") level. Hmmm

Thanks for any help or tips in advance!

Grant

Re: Duplicated decimal coordinate values?

DanPatterson_Retired — Wed, 10 Jan 2018 06:06:26 GMT

How did you calculate those values?

From the Shape field?

using the field calculator?

In ArcMap or ArcGIS Pro?

Re: Duplicated decimal coordinate values?

ERIASGroup — Wed, 10 Jan 2018 06:16:42 GMT

Hi Dan,

Thanks for your questions.

How did you calculate those values?

By right-clicking on the filed name and selecting Calculate Geometry...

Selecting X/Y Coordinate of Point for each separate field and confirming the units in Meters (m) and coordinates are correct.

From the Shape field?

No.

using the field calculator?

Yes

In ArcMap or ArcGIS Pro?

ArcMap (10.5.1)

Thank you.

Re: Duplicated decimal coordinate values?

ERIASGroup — Wed, 10 Jan 2018 06:22:29 GMT

Hi Dan,

Sorry, I did NOT use the Field Calculator.

Apologies for any confusion.

Grant

Re: Duplicated decimal coordinate values?

DanPatterson_Retired — Wed, 10 Jan 2018 06:26:20 GMT

Well if your image is correct the points X and Y values should be distinct as you expect.

On a lark, try the Add XY Coordinates tool from ArcToolbox first. From there, you could try a manual field calculation for the X and Y coordinates separately

Python parser.... in the field calculator

!Shape.centroid.X! and !Shape.centroid.Y! if memory serves

Re: Duplicated decimal coordinate values?

ERIASGroup — Wed, 10 Jan 2018 06:52:25 GMT

Hi Dan,

Once again, thanks for the tips. I have done each method and the results are the same (below).

I'll look for another idea as presently I'm at a loss (and out of time). First time I've seen this actually. Hmmm

I'll let you know when I find a solution.

Many thanks,

Grant

Re: Duplicated decimal coordinate values?

DanPatterson_Retired — Wed, 10 Jan 2018 06:58:24 GMT

I am beginning to suspect that the repeating decimals are due to floating point issues.

Was the featureclass assigned a projected coordinate system when it was created?

If not, there is a long history of geometry errors... albeit small... being introduced. These still exist if geometry is created either in a featureclass or a shapefile, and a coordinate system is not assigned (Define Projection) or assigned during a projection to a projected coordinate system from a geographic coordinate system.

You would have to re-adjust your workflow to include the definition prior to producing a featureclass and calculating geometry values.

Re: Duplicated decimal coordinate values?

ERIASGroup — Wed, 10 Jan 2018 07:12:46 GMT

Hi Dan,

Ok. good thinking. Yes, it's a newly created FC with an assigned CRS before creating geometry. It is part of an ongoing project completely controlled by us and no conversions between projected and geographic coords has occurred.

I will investigate the FC and see if I can duplicate it anew to see if that works.

Cheers,

Grant

Re: Duplicated decimal coordinate values?

XanderBakker — Wed, 10 Jan 2018 12:52:10 GMT

I'm pretty sure that the values return by the Geometry calculation and the Add XY Coordinates—Help | ArcGIS Desktop tool that Dan suggested present the actual coordinates of the geometry. It will be more important to see how the points were created, like were all the points created at the same display scale of the map? Also are you using high precision for your data (in what format is it stored). Was there any snapping applied during the creation of the point geometries?

Re: Duplicated decimal coordinate values?

AbdullahAnter — Wed, 10 Jan 2018 20:31:32 GMT

I can see no problem with duplicated decimal coordinate values.

because they are align and fixed size (grids) polygons .and your points are the center of this polygons

so the coordinates are logical.

Re: Duplicated decimal coordinate values?

EricCollinsOVV — Fri, 12 Jan 2018 14:45:37 GMT

My question back to you regards significance - does it matter? Are you truly measuring to the micrometer (assuming metric coordinates)?

I would guess all the coordinates are relative to your first point and are equidistant integer separations.

If your first point had decimals and everything else is arrayed in exact intervals (eg 10x10 and multiples therof) they all would exhibit the exact same decimal in the coordinate display.

Eg 315752.4077 + 10m east = 315762.4077

Want to make your life simple? Shift your workspace 0.4077 m west and 0.1804 m south.

Re: Duplicated decimal coordinate values?

DanPatterson_Retired — Fri, 12 Jan 2018 14:51:42 GMT

I suspect it is floating point representation when a coordinate system isn't used/defined during the creation of the file... I have seen this too many times. Shifting it will likely produce more errors since the coordinates aren't high precision to begin with

Re: Duplicated decimal coordinate values?

EricCollinsOVV — Fri, 12 Jan 2018 15:00:19 GMT

Respectfully disagree. Every point is relative to the first point created. Every relative point is arrayed and based on an integer grid.

If the first point exhibits floating point coordinates, all all other points will naturally have the same decimals.

It is not a coordinate system problem. If the author had set their first point on an integer coordinate, all other points would have decimals of 0 as well.

Again, the real question to the author is - does it matter?

Re: Duplicated decimal coordinate values?

DanPatterson_Retired — Fri, 12 Jan 2018 15:05:09 GMT

well your tests must differ from mine...but yes, waiting for the OP will solve the mystery

Re: Duplicated decimal coordinate values?

XanderBakker — Fri, 12 Jan 2018 15:10:56 GMT

In case the points are generated based on for instance the center points of the polygons, it would be good to have a look at the coordinates of the polygons, to see if they explain the repeating decimal values (would be logical IMHO).