Technical Log: Overlay a raster map.

[Dapscoptyltd]

I need to establish the projection of the source raster: "".

[Dapscoptyltd]

As discovered in research task #12 British WWI Map Projection, I have established that the Bonne projection was used. However, in the Georeferencer I discovered that CRS systems installed in my QGIS include three Bonne (Werner lat_1-90) projections being:

CRS	Authority ID
Lisboa_Bessel_Bonne	EPSG:102163
Sphere_Bonne	EPSG:53024
World_Bonne	EPSG:54024

This means that I have to ascertain which projection is actually the correct projection. My research used a number of sources:

• epsg.io Coordinate Systems Worldwide.
• Chang, K.-T. (2016), Introduction To Geographic Information Systems, MacGRaw Hill Education.
• Coordinate Reference Systems
• Snyder, J. P. (1987), Map Projections - A Working Manual, Technical report, U. S. Geographical Survey Professional Paper 1395, United States Government Printing Office, Washington.
• GDAL - Geospatial Data Abstraction Library

Having been provided no confirmation, meaning I may have to try several CRSs before one works, which is mentioned in the processes available on the internet. I used the process listed below:

• http://www.qgistutorials.com/en/docs/georeferencing_basics.html

Another possibility is that I will need to use two papers I found and define a proj.4 standard Custom Coordinate Reference System in QGIS. The two papers I found related to this process were:

• Warren, R. Converting British Trench Map Coordinates Tue, 03/05/2013 - 21:56.
• Deakin, R. E. (25-Mar-2015), Coordinate Transformations for World War 1 Topographic Maps, Presented at the Victorian Regional Survey Conference: From the Bush to the Battlefield, Wangaratta, 17-19 April 2015.

I chose the EPSG:102163 Lisbon, Bessel, Bonne reference, to work with first.

Georeferencing 1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4_a.tif

1. Ensured the GDAL georeferencer plug-in was updated.
   • I updated using the plug-in manager, following the prompts.
2. I opened the Georeferencer:
   • Click: Raster > Georeferencer > Georeferencer. -- The geroreferencer window opens.
3. I clicked Open Raster. -- This opens Open Raster window.
   • I selected 1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4_a.tif.
   • Clicked Open. -- The raster map opened.
4. I added Ground Control points. -- These are stored in this Git repository. They are stored on the hard drive as a "[filename].points" file. i. Click Add Point button. The cursor changes to a '+' symbol. ii. Click the point on the raster map (1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4_a.tif). --- The Enter Map coordinates window opens. --- You have two choices here: either going to the vector map, or clicking From map canvas. --- Clicking From map canvas is the easier option as it runs a routine, taking you to your vector map, and changing the cursor to the roundel target shape.
   iii. Select the coordinate location on the vector map (See screenshots below).

5. I added 23 GCP. The example tutorial exercise I was using only used 4.

6. I clicked Settings. -- This loads the Transformation Settings window.

   • I saved the output as "1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4_aOut.tif"
   • I followed the recommended settings: -- Transformation type: Thin Plate Spline; -- Resampling method: Nearest Neighbour. -- Target SRS = EPSG:3395. -- Selected "Load in QGIS when done".

7. I clicked OK.

8. I clicked Start georeferencing.

9. The georeferencing failed.

   • Refer to failure review below.

Appendix 1: Table of GCP points made.

See the repository QGIS/GCP-1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4_a.tif

Failure Error

2017-06-01T22:12:14 1 Raster20170601204248511 :: Layer not found in registry.

Failure review

• My first suspicion was the wrong CRS was chosen.
• My second suspicion relates to the setting: Transformation type found in the "transfomration settings" window. -- I reviewed the settings in this selection point using QGIS documentation. Two points raised questions for me. "The Polynomial algorithms 1-3 are among the most widely used algorithms for georeferencing, and each one differs by the degree of distortion introduced to match source and destination ground control points. The most widely used polynomial algorithm is the second order polynomial transformation, which allows some curvature. First order polynomial transformation (affine) preserves colliniarity and allows scaling, translation and rotation only. The Thin plate spline (TPS) algorithm is a more modern georeferencing method, which is able to introduce local deformations in the data. This algorithm is useful when very low quality originals are being georeferenced." -- I suspect I might need to be using the First order polynomial transformation.

Second Attempt Notes

I followed the procedure carefully with these changes:

• The source EPSG was changed to the EPSG:53024 Bonne Sphere CRS.
  1. I 'loaded' my original raster and noted the changed source.
  2. I then attempted to load the original raster GCP table.
  3. I altered the Settings to change the output file to a new file name (this failed but that was my fault - I overwrote the first output tif file...)
  4. I clicked Start georeferencing.
• The error message displayed: No Raster file loaded' -- This was because I had not selected the source CRS properly apparently.
  5. I clicked Start georeferencing.
• The error measure displayed about there being no GCP table. -- This is a bug. I will have to report that. There appears to be no loading of an existing set of ground control points if you are reusing a image file.
  6. I created a new set of GCPs and this was less than my original 23.
  7. I clicked Start georeferencing.
• It worked.

I partied

Hard

[Dapscoptyltd]

Email text of exchange 02 June 2017 Email GCP AWM.pdf between myself, Dr. Adela Sobotkova, Kerrie Leech, and Dr. Brian Balun-Stanton.

Below are multiple points that require close attention for the next attempt.

The last image shows a black artefact from the lasso - there is no transparency in '.tif' files and QGIS seems to be taking that to be turned into black (adding zeros in the raster file when there is a null value perhaps in the compression matrix).

Might need to set white backgrounds on layers when preparing maps.

[Dapscoptyltd]

Datashare or fig serve for the final data set.