Example 5 – Batch Download Mode – Slovenia

Task: Let us assume we are doing GIS project for government of  Slovenia. They want project in UTM coordinates and in their local datum Hermannskogel. They want us to show them our application can handle as many maps as needed to cover all country in scale 1:25000. They want to see our application running under full load of maps, and they will later provide georeferenced maps of their choice. Maps will be used on screen and printed sometimes, so they want resolution 150 DPI.

We browse maps and locate that country Slovenia is located in area described by UTM coordinates: Zone 33, Band T, Easting: 370000-633000 and Northing 5032000-5196000. That is area of ~ 43 000 square kilometres. 

We will download several map segments, and will use Batch Download Mode. We choose Google Maps, type Hybrid. Since we will be using “Google Anonymous Account”, we decide to set pause between download of two pictures to 60 seconds, so we do not get blocked by the server. We want output in .BMP files with one XML containing all georeferencing data. 

Solution:

First we need to do some calculation. We have 150 DPI device and want maps 1:25 000 in UTM. Resolution 150 DPI means 150 pixels per inch, which is ~2.5cm. That results in 60 pixels per centimetre. One centimetre on map is equivalent to 25 000cm=250 meters in nature. That means 60pix=1cm=250m. That means 1200 pixels is equivalent to 5000 meters. So, you can set map segment width and height to 5000x5000  meters, and target image to 1200x1200 pixels. 

First we setup desired Map source: 


Then we set pause for Batch Download job: 

Then we select Coordinates format: 

Then we select desired output format: 

Then we go set parameters at Batch Download Mode and click Start Batch Job Download:

As it can be seen, this is going to be quite a long Batch Job, since covering whole country of Slovenia requires 1749 maps to be downloaded. We can follow progress of Batch Job: 

We can check detail of Batch Job progress at Log page: 

 

In download folder, 30 hours later, we can check our result. All 1749 map segments covering the whole country of Slovenia  are downloaded:

We can check to see how XML file with georeferencing data looks like. It contains georeferencing data for all 1749 files in one file in XML format:

 

This makes our Task Finished. 

Remark: The main reason why it took so long to download maps is because we set pause to 60 seconds between downloads in order to avoid being blocked by the server. You can test for yourself, sometimes it is enough to put 15 seconds pause or less, so download will be faster.

 


Verification: We want to check how different UTM map segments we got from download align together. For this we will use 3rd party Image processing tool. We will pick two map segments images, then “glue” them together using Image processing tool, then Zoom into picture to see if we can see any discontinuity in enlarged picture. 

First, we deliberately turn one image map into Greyscale, so we can clearly see where images boundaries are. Then we “glue” two pictures together.

Then we Zoom into picture, to level 500%, and see how pictures align together. 

 

As it can be seen, objects like roads appear continuous and without using Greyscale coloring to differentiate between pictures, it would be hard to say where edges are.