Thursday, October 13, 2016

Some differences when opening georeferenced imagery between QGIS and ArcGIS

Just did some minor testing after trying the Georeferencing toolbar in ArcGIS to create some world files (.jpgw, .pngw, .ecww, .tfw, etc.) and wanted to see how these two GIS suites treat the result. Normally I use MapWindow GIS to georeference aerial photos but it's very slow and has some strange bugs that might deserve another blog post.

The aerial photos were received from the provincial agency as MrSID files and were converted to ecw using IrfanView. Neither the original SID files or the ECW files had embedded projection information. In ArcGIS, I used the georeferencing toolbar and added five control points then chose Projective Transformation rather than the default Affine 1st Order Polynomial method to transform the raster. Upon clicking Update Georeferencing (Save the current warp to the dataset) from the toolbar, two files are created with the same name prefix as the .ecw file but with different extensions. They are photoname.ecw.aux.xml, and photoname.ewwx. The .ewwx file contains the image-to-world file transformation parameters using 1st Order Polynomial. The original ecw image file was untouched by this process.

I also made a copy of the photoname.ewwx file and renamed the extension to ecww so there was a file named photoname.ecww that QGIS and MapWindow can use.

It seems that although QGIS can read the ecw.aux.xml for the projection information (so it doesn't need a .prj file), it can not read this auxiliary file's contents for the higher order polynomial transformation. Thus there is a difference in the accuracy of the georeferenced raster when loaded, between ArcGIS and QGIS. In ArcGIS, if a more complex transform higher than 1st order polynomial was used to create the aux.xml and ewwx files, then it will show the raster with the higher order transformation method applied. If one decides to load the raster into QGIS, then QGIS will only use the world file (.ecww) and perform affine transformation on it.

Thursday, June 30, 2016

Friday, April 8, 2016

A list of "All-Weather" tires with the Mountain/Snowflake symbol and where to get them

Though the design and compounds have been around a few years now, it was surprisingly difficult to find tires that are truly All-Weather (good for every season) per Transport Canada standards and meet or exceed the Rubber Association of Canada performance requirements. Since my tires need replacing and I'm not looking for soft winter-specific tires, I have compiled a list of tires that have the mountain/snowflake rating based upon my search. Perhaps you'll find this list useful and that it saves you time.

Nokian pioneered this class of tires and was the first to market but there are now a number of brands with a limited selection.

These makes include: Kumho, Toyo, Falken, Michelin, Vredestein, Hankook, Yokohama, and Nankang, Michelin, Multi-Mile, and Muteki.  Additionally, some are exclusively sold at certain retailers.

Tires that have the 3PMSF icon and are all-weather capable
Manufacturer Model Retailer Size Limits/ Tire diameter
Nokian Nordman WR & WR SUV Kal Tire (Exclusive) Smallest size: 155/70R13 = 21.5", Largest size: 225/55R17 = 26.7"
Nokian WRG3 & WRG3 SUV Kal Tire (Exclusive) Smallest: 175/65R14, Largest: 255/40R19,
SUV Smallest size: 235/75R15 = 28.9", SUV Largest size: 275/40R21 = 29.7"
Nankang SV-2 Kal Tire Smallest size: 175/70R13 = 22.6", Largest size: 235/75R15 = 28.9"
Kumho The Road Venture SAT (KL61) Mopar Dealers (Dodge/Jeep/Fiat),
OK Tire,
Smallest size: 225/75R15 = 28.3", Largest size: 265/50R20 = 30.4"
Kumho Solus HA31 Mopar Dealers (Dodge/Jeep/Fiat), Smallest size: 145/80R13 = , Largest size: 225/45R17 =
Toyo Celsius & Celsius CUV OK Tire,,
Smallest size: 185/65R14
Largest size: 265/50R20
Vredestein Quatrac 3 & Quatrac 3 SUV
Smallest size: 155/70 R 13
Largest size: 255/55 R 19
Vredestein Quatrac 5 2
Hankook Optimo 4S Canadian Tire (Exclusive) Smallest size: 175/65R14 = , Largest size: 225/50R17 =
Yokohama Geolandar A/T G015
Smallest size: 215/75R15 = Largest sizes: 305/55R20 = , 35X12.50R20 = 35"
Falken Wildpeak A/T3W Smallest size: 235/75R15 = , Largest size: 325/60R20 =
BFGoodrich All-Terrain T/A® KO2 Mopar Dealers (Dodge/Jeep/Fiat),
Smallest size: 235/75R15 = , Largest size: 325/60R20 =
Michelin Pilot Alpin PA3 Canadian Tire
Smallest size: = 205/55R16, Largest size: = 285/40R19
Michelin Pilot Alpin PA4 Canadian Tire
Smallest size: 225/40R18 = , Largest size: = 315/35R20
Michelin Primacy Alpin PA3 Canadian Tire
Smallest size: = , Largest size: = 225/45R17
Minerva Emizero 4s Smallest size: = , Largest size: =
Muteki Trail Hog Kal Tire Smallest size: 265/75R16
Largest sizes:
325/60R20 = 35.4",
37X12.5R20 = 37"
Multi-Mile Wild Country XTX Sport Kal Tire 275/65R20 = 34.1"
Nitto EXO Grappler AWT Kal Tire, Smallest size:
Largest sizes:
Nokian Rotiva AT Plus Kal Tire ?

With respect to other tire models that do not have the 3-peaked mountain/snowflake rating yet might actually deliver, however subjective, sufficient or excellent performance in diverse weather conditions including snow, they are not listed here but may be numerous.  Besides reading reviews, it's worth looking at Quebec's Bill 42 (an Act to Amend the Highway Safety Code) passed in 2008 and lists the following as acceptable tires for winter driving: Tires on which one of the following inscriptions appears: Alaska | Arctic | A/T or AT | Blizzard | Ice | LT | Nordic | Snow (but not Mud & Snow) | Stud | Ultratraction | Winter.  Note that after December 15, 2014, in Quebec, these inscriptions on tires were no longer compliant with the statute and only those tires that have the 3-peaked mountain/snowflake
icon are in compliance for winter driving.  
Of course, the class of winter-dedicated tires are probably compliant with Quebec's law but that is not the topic of this blog post.

Wednesday, March 16, 2016

A simple way to view Shadow Copies on Windows 8.1 without installing or downloading software

Upon pressing "undo" accidentally in File Explorer on my Surface Pro 3, Windows 8.1 performs bad behaviour.  See details and frustration others have had here: thread

It seems Windows 8.1 made all the contents of the folder disappear as a consequence of undoing a previous rename of the folder from "New Folder".  That is, the file entry in the Master File Table was lost. Hopefully the entries were deleted and the space is reusable (I'm not sure what how Windows manipulates the MFT in this case).

So, I wanted to recover the files from that folder.  I first found out that Windows 8 has two kinds of "backup" systems, one called File History that is intended to make regular replicas of the tracked Libraries to a separate physical disk or to a network share.  Since this File History wasn't configured and not turned on by default on my SP3, I looked toward Volume Shadow Copy, which appears to be enabled by default on the C: drive.  You can check your "System Protection" tab in System Properties to see if this is the case for you by following the first part of this tutorial:
In fact, you can follow the entire video if you feel you want to try the software he mentions, ShadowExplorer.

Alternatively, if you don't want to download any software and happen to have a Windows 7 Pro machine at your disposal on your network, then you can just navigate to the Windows 8.1 machine and right click the folder of interest to see Previous Versions.  This is how I recovered my files and viewed the snapshots of my Documents folder on my SP3.

Interestingly, if you try navigating to \\localhost\C$ on the Windows 8.1 computer without any software installed, you'll be able to see the Previous Versions tab, but it will be empty.  So in my case, from the Windows 7 Pro machine, I navigated to \\SP3\Users\name\Documents\ and right-clicked properties on the folder of interest.  This showed me Previous Versions with a list of snapshots and their dates.

I was afraid at first that I didn't have any shadow copies to restore because checking the Services tab in Task Manager on my SP3 indicated the VSS (Volume Shadow Copy) service was Stopped.  Also, this article says that Volume Shadow Copy Service in Windows 8 is set to manual and does not run on system startup.  Lucky for me, Shadow Copies were being made and I was able to use a Windows 7 computer on the same network to browse the "Previous Versions" of the folders on the SP3 running Windows 8.1 without even downloading other software such as ShadowExplorer mentioned above or Z-VSScopy.