topic Re: Issues in projection while defining data frame extent by coordinates in Python Questions

Issues in projection while defining data frame extent by coordinates

BenjaminBauman — Thu, 05 Feb 2015 23:54:51 GMT

I'm trying to set the following coordinates to a dataframe:

custom_extent = {1:-87.678956, 2: -87.611652, 3:41.867129, 4:41.954932}

where `1` is key for `XMin`, `2` is key for `XMax`, `3` is key for `YMin`, and `4` is key for `YMax`

However, when I try to set the new extent up, the coordinates are not the results I expect. Here's a code snippet:

print data_frame.extent.XMin # prints 480718.855003

original_spatial_reference = data_frame.spatialReference

newExtent = data_frame.extent

data_frame.spatialReference = arcpy.SpatialReference("WGS 1984")

print data_frame.extent.XMin # prints -87.6986700746

newExtent.XMin, newExtent.XMax = custom_extent[1], custom_extent[2]

newExtent.YMin, newExtent.YMax = custom_extent[3], custom_extent[4]

data_frame.extent = newExtent

print data_frame.extent.XMin # prints -93.500018925

data_frame.spatialReference = original_spatial_reference

print data_frame.extent.XMin # prints -2.38749449402

Every printout does not match the desired `XMin`: `-87.678956`. Any thoughts?

Re: Issues in projection while defining data frame extent by coordinates

DanPatterson_Retired — Fri, 06 Feb 2015 00:08:46 GMT

The extent object normally defines the lower left and then the upper right, check that you have your numbers in the correct order ArcGIS Help (10.2, 10.2.1, and 10.2.2)

Re: Issues in projection while defining data frame extent by coordinates

BenjaminBauman — Fri, 06 Feb 2015 00:20:36 GMT

Dan, I''m not sure I follow.

When I reorder the dictionary keys in the following lines:

newExtent.XMin, newExtent.XMax = custom_extent[1], custom_extent[2]

newExtent.YMin, newExtent.YMax = custom_extent[3], custom_extent[4]

I still am not seeing satisfactory results. Is this what you are referring to?

Re: Issues in projection while defining data frame extent by coordinates

DanPatterson_Retired — Fri, 06 Feb 2015 00:56:45 GMT

ok...not used to seeing extents that way...I have seen that issue before and I had to go into the layer properties and recalculate the extent of the layer manually and in some instances export the file to a new one before the extents in the new coordinate system are updated. It appears that setting the extent object isn't enough and I haven't been able to find an arcpy property/method to update one. I notice this translating coordinates in an arbitrary World mercator projection centered around 0,0 then redefining the coordinate system to a modified transverse mercator shifted by 300,000 in X and 5,100,000 in Y. Oddly, the lower extent was retained (around 0,0) yet the upper was correct. So in short...not definitive answer but you aren't alone

Re: Issues in projection while defining data frame extent by coordinates

JasonSchwartz — Fri, 06 Feb 2015 01:22:32 GMT

Ben,

There's a comment in the documentation for the Extent property of the DataFrame class: "If the aspect ratio of the extent does not match the shape of the data frame, the final extent will be adjusted to fit the new extent within the shape of the data frame. In other words, if you set explicit X, Y coordinates, you may not get the same values returned if you attempt to read them later. " <--I suspect this is what is partly the cause of what's happening.

A second contributing factor may be the dataFrame object is assigned out of an 'original_spatial_reference' into 'WGS 84' then back into the original spatial reference again. -- although there isn't print out of what the original is.

Here's my request: please print out the original_spatial_reference, the dataframe map units, and the elementWidth, elementHeight at each step in the routine: before you start, during the assignments, and before/after each spatial reference shift. -- The last two properties will let us look at the dataframe aspect ratio which is held constant during the assignment of Mins and Maxs.

Lastly, while in WGS84, try setting the extent of your MXD by hand using those input values, then shift spatial references back to your original spatial reference and map units, then interrogate the MXD to look for those odd printed out values. (the ones that look like UTM meters and/or decimal degrees.)

Good news is that your custom_extent array and newExtents assignments are formatted correctly; there should be nothing wrong with these.

Please reply back with what printouts arcpy gives at each step and we'll proceed from there.

Jason S. aka JasonInVegas

Re: Issues in projection while defining data frame extent by coordinates

DanPatterson_Retired — Fri, 06 Feb 2015 01:55:16 GMT

Interesting Jason, but I have experience weird extent behaviour when working solely with arcpy (ie no ArcMap open and no *.mxd referenced). I will try to post a demo when I get off this iThingy and on to my desktop.

Re: Issues in projection while defining data frame extent by coordinates

BenjaminBauman — Fri, 06 Feb 2015 02:15:40 GMT

Jason - the documentation makes sense in that regard - if the dimensions of the data frame differ from the received coordinates, naturally they're not going to be precise. However, as you know, this goes beyond that problem.

The following printout reflects a set of print statements done prior to every line seen above, with an additional set of print statements following the last line.

XMin 480718.855003

XMax 487765.034905

YMin -897522.367118

YMax -892753.723682

mapUnits Meters

spatialReference <geoprocessing spatial reference object object at 0x0D2102D8>

elementWidth 13.6918

elementHeight 9.2662

XMin 480718.855003

XMax 487765.034905

YMin -897522.367118

YMax -892753.723682

mapUnits Meters

spatialReference <geoprocessing spatial reference object object at 0x0D210428>

elementWidth 13.6918

elementHeight 9.2662

XMin 480718.855003

XMax 487765.034905

YMin -897522.367118

YMax -892753.723682

mapUnits Meters

spatialReference <geoprocessing spatial reference object object at 0x0D210410>

elementWidth 13.6918

elementHeight 9.2662

XMin -87.6986889715

XMax -87.6353211223

YMin 41.9155057359

YMax 41.9583911976

mapUnits DecimalDegrees

spatialReference <geoprocessing spatial reference object object at 0x0D210410>

elementWidth 13.6918

elementHeight 9.2662

XMin -87.6986889715

XMax -87.6353211223

YMin 41.9155057359

YMax 41.9583911976

mapUnits DecimalDegrees

spatialReference <geoprocessing spatial reference object object at 0x0D210410>

elementWidth 13.6918

elementHeight 9.2662

XMin -93.500046392

XMax -93.4999395774

YMin 50.1891561644

YMax 50.1892284534

mapUnits DecimalDegrees

spatialReference <geoprocessing spatial reference object object at 0x0D210410>

elementWidth 13.6918

elementHeight 9.2662

XMin -5.44407670288

XMax 6.44407996557

YMin -0.0228719610641

YMax 8.02267627373

mapUnits Meters

spatialReference <geoprocessing spatial reference object object at 0x0D210410>

elementWidth 13.6918

elementHeight 9.2662

I will try setting the extent manually tomorrow when I have more time.

Re: Issues in projection while defining data frame extent by coordinates

BenjaminBauman — Fri, 06 Feb 2015 02:17:12 GMT

Dan, I appreciate your help in all of this. I also tend to see differences in result when I'm using ArcPy with mxd set as "CURRENT" vs running ArcPy via a standalone script.

Re: Issues in projection while defining data frame extent by coordinates

JasonSchwartz1 — Sat, 28 Feb 2015 17:07:57 GMT

Hey Ben, this looks just like you described (and baffling to me.) Can you sub-qurey into the spatialReference object to printout more than the in-memory Object handle? The goods (i.e. reason for this madness) may be contained therein.

How about including these properties: sO.projectionname; GCSname; linearunitcode <-- that one may be the key.

Good luck!

Re: Issues in projection while defining data frame extent by coordinates

BenjaminBauman — Sat, 28 Feb 2015 18:04:54 GMT

Hey Jason, I've pretty much given up this approach in favor of a roundabout method of setting the dataframe extent by zooming to selected features. Perhaps I'll go about doing a printout of those properties at some point down the road, but for the time being, I've moved on to other things (partially out of frustration, and partially out of time constraints).

I'm shocked that something so simple could be such a challenge to implement.

Re: Issues in projection while defining data frame extent by coordinates

JoshuaBixby — Sat, 11 Dec 2021 15:43:39 GMT

Try building the Extent object from scratch instead of reconstructing one you get from the DataFrame object. If I understand what you are expecting for results, the following code works for me in the interactive Python window in ArcMap:

custom_extent = {'XMin':-87.678956, 'XMax':-87.611652, 'YMin':41.867129, 'YMax':41.954932}
newExtent = arcpy.Extent(**custom_extent)

print data_frame.extent.XMin
data_frame.spatialReference = arcpy.SpatialReference("WGS 1984")
print data_frame.extent.XMin

data_frame.extent = newExtent
print data_frame.extent.XMin

If you want to use a dictionary to store an extent's bounds, may I suggest using key names that correspond to function parameters. That way, you can just pass the dictionary as keyword arguments to an Extent function.

Update: It dawned on me after posting the code above why your original code might not be working. I believe it fails because you change the spatial reference of the data frame after getting the extent object from the data frame. If you change the spatial reference first, it seems to work.

custom_extent = {1:-87.678956, 2: -87.611652, 3:41.867129, 4:41.954932}

print data_frame.extent.XMin
data_frame.spatialReference = arcpy.SpatialReference("WGS 1984")
print data_frame.extent.XMin

newExtent = data_frame.extent
newExtent.XMin, newExtent.XMax = custom_extent[1], custom_extent[2]
newExtent.YMin, newExtent.YMax = custom_extent[3], custom_extent[4]
data_frame.extent = newExtent
print data_frame.extent.XMin