topic Re: Spatial reference extent limitations ? in Python Questions

Spatial reference extent limitations ?

TieshengWu — Tue, 17 Jul 2018 01:40:59 GMT

I would like to get features spatial reference limitations of coordinate x and y by using snippet like:

sr = arcpy.Describe('my feature').spatialReference

dom=sr.domain.split()
xmin=float(dom[0])
ymin=float(dom[1])
xmax=float(dom[2])
ymax=float(dom[3])

...

But it seems don't work. For a WGS84 GCS, the result is xmin=-180, xmax=180, ymin=-90 but ymax=270 rather than 90, and more strange result for a WGS84 PCS. Does sr.domain is not proper for my needs?

Re: Spatial reference extent limitations ?

DanPatterson_Retired — Sat, 11 Dec 2021 07:56:01 GMT

Interestingly... if you run the code snippet for a gcs wgs84 from

SpatialReference—ArcPy classes | ArcGIS Desktop

You get some strange results.

Perhaps Melita Kennedy‌ can offer some insight

wkt = "GEOGCS['GCS_WGS_1984',DATUM['D_WGS_1984',SPHEROID
             ['WGS_1984',6378137.0,298.257223563]],\
              PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]],\
              VERTCS['WGS_1984',DATUM['D_WGS_1984',SPHEROID
             ['WGS_1984',6378137.0,298.257223563]],\
               PARAMETER['Vertical_Shift',0.0],PARAMETER['Direction',1.0],UNIT
             ['Meter',1.0]];\
               -400 -400 1000000000;-100000 10000;-100000 10000;8.98315284119522E-09;\
               0.001;0.001;IsHighPrecision"

sr = arcpy.SpatialReference() sr.loadFromString(wkt)

r.domain

'-400 -400 9006799.25474099 9006799.25474099'‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Spatial reference extent limitations ?

JoeBorgione — Sat, 11 Dec 2021 07:56:04 GMT

What is your objective? Are you most concerned with the actual Spatial Reference of your data or are you concerned with extent of your data?

If the latter, consider the snippet of code below that returns the XMin/Max YMin/Max of a given feature class (fc):

fc = 'YourFeatureClass'
descFC = arcpy.Describe(fc)
fc_xmin = descFC.extent.XMin
fc_ymin = descFC.extent.YMin
fc_xmax = descFC.extent.XMax
fc_ymax = descFC.extent.YMax

print 'Extents of {}, {}, {}, {}, {}'.format(fc,fc_xmin,fc_ymin,fc_xmax,fc_ymax)

‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Spatial reference extent limitations ?

TieshengWu — Tue, 17 Jul 2018 15:05:54 GMT

Thanks for your responding Joe. My concern is the largest extent limit of any coordinate system, GCS or PCS. The problem arise from a practical problem, that is, when a polygon feature is create using ArcPy, the limit extent of the coordinate system may be exceeded and making the feature invalid.

Re: Spatial reference extent limitations ?

JoeBorgione — Tue, 17 Jul 2018 15:20:05 GMT

I am dealing with a similar issue with respect to extents. (See: Spatial Extents ). When I append source data to a (emtpy) target the the extents are sometimes well out of bounds my area of interest. Allegedly, the process of appending re-calculates the extent, and I've had that happen. But, I still get feature classes that have an extent of USA and the Philippines when all the data should reside in one county, in one state of the US.

When you define an empty feature class with a given spatial reference, it is given the extents of 0,0,0,0. Once you add features to the feature class, the extent is supposed to be that of the features themselves...

Re: Spatial reference extent limitations ?

TieshengWu — Tue, 17 Jul 2018 15:42:19 GMT

Yes it's helpful. But in my situation, the spatial reference of the feature is unknown in advance, so I must have a method to get the limit extent and using that in my code to avoid the out of extent error.

Re: Spatial reference extent limitations ?

JoeBorgione — Tue, 17 Jul 2018 16:03:03 GMT

If you find it let me know! I would like to restrict my extents as well, and the only thing I can come up with is clip it once it has data in it.

Re: Spatial reference extent limitations ?

DanPatterson_Retired — Tue, 17 Jul 2018 17:29:34 GMT

You set the extents to a featureclass not the actual projection itself since a projection doesn't have the extent property as you have found out.

Re: Spatial reference extent limitations ?

JoeBorgione — Tue, 17 Jul 2018 18:39:14 GMT

Dan- how do I set the extents using arcpy?

As mentioned in my other thread that you responded to: We take data from the authoratative source and append to a 'public' enterprise geodatabse. The source data can be wonky with respect to extents. I'd love to control the append in such a way that just those features within a given xmin, ymin, xmax, ymax extent are appended...

Dan Patterson‌

Re: Spatial reference extent limitations ?

DanPatterson_Retired — Tue, 17 Jul 2018 18:48:33 GMT

I set extents explicitly, but I don't rely on reading a coordinate system at all (prj etc) or even a featureclass, unless I have to.

I simply know the bounds of where I am working, set it accordingly and check the geometry (a big point in polygon def) to ensure all is where it should be.

But! you people are using that enterprise and sde thing.... my only suggestion is to create a big Area of Interest file (AOI) and simply do a select by attribute to see if your features intersect, (or whatever) with your AOI.

Re: Spatial reference extent limitations ?

JoeBorgione — Tue, 17 Jul 2018 19:07:46 GMT

That's what I've come up with: I created a polygon based on the extent of the county. It's the automation part that fails: the RecalculateFeatureClassExtend_management() method only takes one argument and that's the feature class itself. If it were to take 5 (name, xmin,ymin,xmax,ymax) I'd be golden!

Re: Spatial reference extent limitations ?

MelitaKennedy — Sat, 11 Dec 2021 07:56:07 GMT

It's pulling the spatial reference xy domain which is square. The lower left / minimum values are good, but the max values may be blown out to either make the extent square or to make the xy resolution value a reasonable number.

The -400 is to cover data that could be in -360 to 0 longitude range, with a very generous buffer added. We just used the same value for the minimum Y (latitude) value too.

-400 -400 1000000000;-100000 10000;-100000 10000;8.98315284119522E-09;\
               0.001;0.001;IsHighPrecision"

These values are (in order):

minimum X, minimum Y, inverse of xy resolution;

minimum Z, inverse of Z resolution;

minimum M, inverse of M resolution;

XY tolerance;

Z tolerance;

M tolerance

True that the spatial reference is high precision versus the original "basic" precision.

The tolerance values are actually not good if the data is using a geographic coordinate system.

Wu Teshieng, you probably want the coordinate system's "projected horizon" but I don't think that's exposed in arcpy. Here's some of the methods in ArcObjects:

https://desktop.arcgis.com/en/arcobjects/latest/net/webframe.htm#iprojectedcoordinatesystem4_getpcshorizon.htm

The PCS horizon but in latitude/longitude. It is not guaranteed to be an inclusive horizon (it might be exclusive to show which part of the world can't be 'seen' in the particular PCS).

https://desktop.arcgis.com/en/arcobjects/latest/net/webframe.htm#iprojectedcoordinatesystem2_gethorizon.htm

Re: Spatial reference extent limitations ?

TieshengWu — Wed, 18 Jul 2018 01:49:50 GMT

Thanks for your instruction Melita. Yes, what I want is exactly the valid area of a coordinate system, so i know now it's called 'project horizon' (but a GCS also have a limit boundary by longtitude and latitude for -180 to 180 and -90 to 90 degree ). It's a pity that arcpy can't retrieve this value. Can i insert ArcObject codes in arcpy to get it?

Re: Spatial reference extent limitations ?

MarcoBoeringa — Sun, 30 Jun 2019 13:50:36 GMT

Melita Kennedy schreef:
It's pulling the spatial reference xy domain which is square. The lower left / minimum values are good, but the max values may be blown out to either make the extent square or to make the xy resolution value a reasonable number.

Melita Kennedy,

Could these specific traits of the "domain" properties of a Spatial Reference be better documented on the Help page of the Spatial Reference?

I was running into a similar issue, where calling:

spatialRefDomain = spatialRef.domain
arcpy.AddMessage("spatialRefDomain: " + spatialRefDomain)

to inspect the extent's values, resulted in rather un-expected max values (spatialRefDomain: -20037700 -30241100 900699887774,099 900689684374,099), as I didn't realize these were related to the XY resolution of the dataset. The first impression of the "domains" is that they represent something like the "projection horizon" you mentioned, but your explanation makes clear they are something entirely different. I think the difference must be cleared up in the Help page of the Spatial Reference as well by adding extra documentation. The current page is rather minimal in explanations (although it is comprehensive in mentioning all properties). It probably could use some graphics as well to give some visual impression of these properties.

Re: Spatial reference extent limitations ?

MarcoBoeringa — Sun, 30 Jun 2019 14:03:21 GMT

Actually, adding the "Note" text mentioned on the

Recalculate Feature Class Extent—Help | ArcGIS Desktop

Help page thatJoe Borgione‌ pointed out and that mentions the difference between domains and extents, to the Spatial Reference Help page, would already be a big win.