Round 2 in which ArcGIS throws in the towel.
(Please note: This post is about clipping in ArcGIS version 10.0. The functionality has been improved, and problems mentioned have been fixed in later versions of ArcGIS)
This is a follow-up to my previous post where I matched up ArcGIS and QGIS in a clipping contest. One of the commenters on that post expressed some concern that there might be “…something else going on…” with my test, and I agreed. It was unfathomable to me that an ESRI product could be out-done by such a wide margin. Knowing that ArcGIS often has problems processing geometries that are not squeaky clean, I began my investigation there. I ran the original contour layer through ArcToolbox’s Check Geometry routine, and sure enough, came up with 5 “null” geometries. I deleted those bad boys, and ran it through ArcToolbox’s “Repair Geometry” routine, and then ET GeoWizard’s “Fix Geometry” routine for good measure (These may or may not be identical tools, I do not know). No new problems were found with either tool.
I wanted to give ArcGIS a fighting chance in this next round, but also wanted to level the playing field a bit. I did a restart of my Dell m2400 (see the specs in the previous post), exited out of all my desktop widgets, and turned off every background process I could find. I also turned of Background Processing in the Geoprocessing Options box. The only thing running on this machine was ArcGIS 10, and the only layers loaded were the contour lines and the feature I wanted to clip them to. I ran the “Arc Toolbox > Analysis Tools > Extract > Clip” tool and watched as it took 1 hour 35 minutes and 42 seconds for ArcGIS to go through the clipping process before ending with the message:
ERROR 999999: Error executing function
Invalid Topology [Topoengine error.]
Failed to execute (Clip)
Now granted, this is much better than the 12 hours it took the first time I ran it, but still, no cigar in the end.
Giving QGIS a chance to show it’s stuff, I used Windows version 1.5.0 to run a clip on the same files, on the same machine. QGIS took all of 6 minutes and 27 seconds to produce a new, clean contour layer.
I ran this through the same geometry checks as the original contour layer, and came up with no problems.
My goal here is not to jump all over ESRI and do a dance in the end zone. I would really like to figure out what’s going on. As I’ve said before, I’ve had problems in the past with ArcGIS producing bad geometries with its Clipping process (and other tools, too). But the fact that another product can handle the same set of circumstances with such ease baffles me.
I’ve put about as much time as I can into this test, and taken it as far as I can. If you would like to give it a go, feel free to download the files I used through his link:
(Note: This is a 878MB file, and is not completely uploaded as of this posting. Check back later if the link does not work for you right now)
If any of you have better results than I did, or find any faults with my files or process, please let me know and I WILL make a note of them here. Thank you.