Sunday, March 26, 2017

Assigning single attribute to multi geometric features in QGIS

There are situations when you will want as many as possible geometric features within a shapefile layer to share the same attribute information within the attribute table.

This kind of scenario is commonly seen when representing Islands. The attribute data is the same, but the geometric representation of the Islands (in polygon) will be separated from each other to give way too water bodies.

As an example, am going to use a Nigerian state the has Islands (Bayelsa state). So, to digitize Bayelsa into wards polygons we have to deal with Islands. And here I have three polygons representing the same ward with ward_code 12 as seen below.

So, the task here is to merge or combine these same attributes into one and all the three polygons will share that same attribute information/row.

In QGIS, to make multiple polygons share the same attribute proceed like thus:-
1) First digitize the Islands polygons and assign the same attributes as usual
2) Go to Vector Menu >> Geometry Tools >> Singleparts to Multiparts

3) The next window will prompt you for the input layer (from a drop-down list) and the Unique ID field (Ward_Code) and you can specify an output file name. Select the appropriate information and click on run.

4) You should now have multi polygons sharing one row of your attribute table

Alternative method

Alternatively, you could use the "Merge Selected Features" command available in the Advanced Digitizing Toolbar as seen below:-

Select the polygons you want to merge there attributes and click on "Merge Selected Features" within the "Advanced Digitizing Toolbar", configure the attributes accordingly and click on "Ok".

That is it.
Thanks for following.

Wednesday, March 22, 2017

Using Python OpenCV to detect human face on Nigeria currency notes


Below is a short video clip of a project am working on. It shows you about: Using Python OpenCV and Haar Cascade for Detecting human face on Nigeria currency notes

Happy viewing!

Saturday, March 11, 2017

How to merge multiple shapefile layers into one big shapefile layer

In QGIS, there are two common ways to merge multiple vector layers into one big vector shapefile layer. Namely:-

1) Using "Merge Vector Layers"
2) Using MMQGIS Plugin

I will only talk about the first option, since it is the default option made available in QGIS. For the second option, you will have to install the MMQGIS Plugin accordingly.

Merging multiple vector layers using "Merge Vector Layers"

This function is available under the menu Vector | Data management tool. You can merge all files in the input directory or select specific files in the input directory.

This algorithm combines two vector layer of the same geometry type into a single one. If attributes tables are different, the attribute table of the resulting layer will contain the attributes from both input layers.

The same applies as for MMQGIS Plugin: merged layers must all be of the same geometry type. Also, if the source layers have different attributes fields, the merged file will contain all fields, but with NULL values inserted when a source layer does not have a specific field.

Thanks for following.

Saturday, March 4, 2017

How to download Satellite or Google earth Images with High Resolution

Hey there,
Few years ago, I published a YouTube video demonstrating how to do this using El-Shayal GIS software.

Since then, many things have changed including OS etc. So today, I decided to add more options to the list.

There are multiple solutions for downloading a satellite image at high resolution. Some commonly used solutions are listed below:-

1- AutoGR software

This a powerful geometry coordinate and statistical software.

2- Map Puzzle software

If you want to download some map location from Google Maps, Bing Maps or any other map service, Map Puzzle is just what you need! It will allow you to save your map locations into high resolution images (jpg, gif, png, bmp, tiff). The only thing you need to do is to enter GPS coordinates or address by GeoCoding, hit "Download" and you are done! The map has been saved into to your computer. It works on Windows XP, Windows Vista, and Windows 7. Requires no installation and its FREE.

3- Elshayal software

Elshayal Smart is a freeware map editor app filed under mapping and made available by Elshayal Smart Web on Line Software for Windows.

4- SAS planet software

SASPlanet is a program designed for viewing and downloading high-resolution satellite imagery and conventional maps submitted by such services as Google Maps, DigitalGlobe, Kosmosnimki, Yandex.Maps, Yahoo! Maps, VirtualEarth, Gurtam, OpenStreetMap, eAtlas, Genshtab maps, iPhone maps, Navitel maps, Bings Maps (Bird's Eye) etc., but in contrast to all these services all downloaded images will remain on your computer and you will be able to view them, even without connecting to the internet. In addition to the satellite-based maps you can work with the political landscape, combined maps and maps of the Moon and Mars.

5- Google map downloader software

Google Maps Downloader helps users design custom maps by using geographical coordinates. Maps downloaded through this app can be arranged together to form one large map, or viewed individually. The Google Maps Downloader interface is practical and user-friendly.

6- Universal Maps Downloader

Universal Maps Downloader is a tool that help you to get small tile images from Google Maps, Bing maps, OpenStreet Maps, Yandex Maps, Ovi Maps, MapQuest Maps, etc. All downloaded small images are saved on the disk. You can view downloaded maps by Maps Viewer Or you can combine them into a big bmp, jpg or tif file by Maps Combiner, and also you can export all tiles into a MBTiles format database.

7- Global Mapper

Global Mapper is an affordable and easy-to-use GIS application that offers access to an unparalleled variety of spatial datasets and provides just the right level of functionality to satisfy both experienced GIS professionals and beginning users.

8- USGS Earth Explore

9- BigEast Map Downloader

There are definitely more than those mentioned above. If you know any that is worth knowing feel free to list it in the comment box below.

Thanks for reading