I needed to prepare a raster map to overlay onto my sample map project, to confirm it was possible and that I could do it. This meant preparing an image file from a map file.
Upon conferring with Dr. Adela Subotkova, I confirmed that the printed map should be converted into an image file.
Confirming my OSM Map was linked to the correct CRS
To ensure that any raster file imported to my map was correctly projected, I needed to confirm what my existing CRS was, and that it was correctly chosen for my map and the region.
I had downloaded, as my first map a source from:
The CRS chosen for the OSM street map was WGS 84 / World Mercator.
I noted that the datum code for this projection was:
+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
The project properties window:
Testing the coordinates
To obtain a correct North and East coordinate for testing my OSM map and CRS choices in QGIS, I chose the intersection of Langemarkstraat, Ieperstraat, and Roeselarestraat in Zonnebeke. The exact point chosen was the rendered "centre" of the roundabout. This intersection is in front of the
Onze-Lieve-Vrouwkerk, another prominent landmark on maps.
Step One
Using the guide found here, I obtained northing and easting points from Google Maps:
50°52'21.8"N 2°59'15.7"E
50.872731, 2.987694. This is the N, E latitude and longitude coordinates format from the datum location.
The results are shown in the figure above.
The latitude and longitude coordinates are of the most interest and confirm in my mind that this was an accurate (certainly for the purposes of this exercise). 2° is very close to Greenwich, and its positive number showed it as an easterly direction. The 50° bearing for latitude also is indicative that this bearing was accurate.
Step Two
I confirmed my project settings in QGIS for map and CRS were as above.
On my OSM map layer, I zoomed into the intersection of Langemarkstraat, Ieperstraat, and Roeselarestraat in Zonnebeke, to the rendered "centre" of the roundabout.
I selected the OSM Tools button.
I clicked the Map Coordinate.
-This turned the cursor into a target.
I selected the centre of the roundabout.
The From Map values from my selection with the cursor target were:
-- 2.98770, 50.87272, which is an 'x', 'y' coordinate, where 'x' = North and 'y' = East.
While this is far from an exhaustive test, I accept that for the purposes of this exercise, this is enough to confirm the CRS for this sample project's OSM map are correct.
Further Image creation Research
I made a few searches in Google to ascertain hidden problems:
Importing a printed map into QGIS
problems Importing a printed map into QGIS
The results were limited.
When you convert the image make sure it is NOT saved in a progressive format, especially if you are using GIMP (where this is the default).
-- "Progressive" changes the encoding to display the image at increasingly higher quality levels until the image is fully loaded. QGIS is expecting standard encoding. It is related to a compression maths used to create the file itself, where compression occurs in multiple passes, where the standard image compression model is a discrete cosine transform - ideally suited to geometric mathematical conversions in a GIS context. (From wikipedia and professional experience).
To georeference the image go Raster->Georeferencer (however I will be using the QGIS tutorial procedure where you do this task as you commit the file as an overlay raster file.
Prepare the Raster map tif file
This map needed to be, as confirmed by Dr. Sobotkova, converted into a raster graphic I chose a tif file without progressive compression.
This map also needed information removed.
The conversion was thus chosen to be performed in Adobe PhotoShop, but many graphic software packages could be used.
In Adobe Photoshop I opened the file "1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4.pdf" (for more information refer to my #9 Technical log).
I saved it as "1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4.tif.
I unlocked the background layer.
Next I needed to remove the extremities of the map and the legend.
This is done with the Lasso tool.
It has a number of options.
I chose the Polygonal Lasso tool, because it is best for straight edge trimming like this.
I entered a cut line.
I selected Layer > Inverse.
I then deleted the selected sections.
Save as 1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4.tif
This file had a large white space section in the top left as a result of removing the legend.
I cropped the file and saved that as "1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4_a.tif"
I opened the original tif and cropped that image, and saved as "1917-10-10_19-00_D11toK2EA_SitMap_RCDIG1014546-4_b.tif"
These files are attached to #9 to explain file saving conventions.
Intro
I needed to prepare a raster map to overlay onto my sample map project, to confirm it was possible and that I could do it. This meant preparing an image file from a map file.
Upon conferring with Dr. Adela Subotkova, I confirmed that the printed map should be converted into an image file.
Confirming my OSM Map was linked to the correct CRS
To ensure that any raster file imported to my map was correctly projected, I needed to confirm what my existing CRS was, and that it was correctly chosen for my map and the region. I had downloaded, as my first map a source from:
The CRS chosen for the OSM street map was WGS 84 / World Mercator.
+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defsThe project properties window:
Testing the coordinates
To obtain a correct North and East coordinate for testing my OSM map and CRS choices in QGIS, I chose the intersection of Langemarkstraat, Ieperstraat, and Roeselarestraat in Zonnebeke. The exact point chosen was the rendered "centre" of the roundabout. This intersection is in front of the Onze-Lieve-Vrouwkerk, another prominent landmark on maps.
Step One
Using the guide found here, I obtained northing and easting points from Google Maps: 50°52'21.8"N 2°59'15.7"E 50.872731, 2.987694. This is the N, E latitude and longitude coordinates format from the datum location.
The results are shown in the figure above.
The latitude and longitude coordinates are of the most interest and confirm in my mind that this was an accurate (certainly for the purposes of this exercise). 2° is very close to Greenwich, and its positive number showed it as an easterly direction. The 50° bearing for latitude also is indicative that this bearing was accurate.
Step Two
Step Three
While this is far from an exhaustive test, I accept that for the purposes of this exercise, this is enough to confirm the CRS for this sample project's OSM map are correct.
Further Image creation Research
I made a few searches in Google to ascertain hidden problems:
This forum response proved helpful.
Prepare the Raster map tif file
This map needed to be, as confirmed by Dr. Sobotkova, converted into a raster graphic I chose a tif file without progressive compression. This map also needed information removed. The conversion was thus chosen to be performed in Adobe PhotoShop, but many graphic software packages could be used.
These files are attached to #9 to explain file saving conventions.