How to do Proximity analysis in QGIS?

Proximity is a neighbourhood function of GIS. It is similar to buffer analysis that we do for Vector but if it’s done for Raster then it is called proximity in GIS. 

In this article I’m going to show how it’s done in QGIS.

Since, there will be distance measurement make sure you use Projected coordinate system which has unit meters instead of Geographic coordinate system. Here I will be using WGS84 44N.

Follow the following steps:

Step 1: Loading data

Load your raster data ‘Raster_road’ in QGIS simply by dragging it to layer panel.

Step 2: Processing Toolbox

Go to Processing toolbox search for ‘Proximity’ under Raster analysis of GDAL section you will get ‘Proximity (raster distance)’ double left click it to get below interface.

Step 3: Parameters settings
Give input layer ‘Raster_road’, distance units ‘Georeferenced coordinates’, Max distance to generate ‘1500’, No data value to use as ‘Not Set’ and save it to as file ‘Proximity_road’ and run it.

Here we used Georeferenced unit as distance units so that output raster will have cell values representing no. of units in the current Coordinate Reference System(CRS), with each cell from Raster_road.

On successful run you will get following output.

Step 4: Symbology

Double left click ‘Proximity_road’ layer -> Symbology -> Make max value as ‘1500’(since we want range of buffer to 1500 only) -> click apply

Finally, you will see following output.

So, that’s all from us for today.

Happy analysis!

How to convert vector to raster in QGIS?

Converting a vector to a raster is a very common process in GIS. In this tutorial I’m going to show how it’s done in QGIS in detail.

Follow the following steps:

Step1: Load your desired vectors in layer panel like shown below. Here I will rasterize ‘clipped_building’ vector.

Step2: Processsing Toolbox panel

Go to Processing Toolbox panel -> search ‘vector to raster’, -> under Vector conversion of GDAL section you will get Rasterize(vector to raster).

Step3: Choosing parameters

In input layer select vector that you want to rasterize, choose 1 as fixed value to burn, Georeference units as output raster size units, 15 as Width/Horizontal and Vertical/Height, Output extent as butwal_44N, Assign no data value as Not set. At last save it to a file as ‘Rasterized’.

Remember values you choose depends on for what purpose you are going to use the raster.

If everything is fine you will see output like this.

Definitions

Burn in value: pixel value that represents data(if set to 1 then your data will be white and rest all black).

No data value: invisible region outside the main data.

Vertical/Horizontal resolution: Determines no. of cells/pixels your raster will be formed. If you will give high resolution value then no of cells will be reduced and output raster resolution will be reduced and vice-versa for Georeferenced units.

Output raster size units:

Pixel units: Suppose if you set Vertical/Height resolution and  Horizontal/Width resolution as 5 then output raster will have pixels of 5 rows and 5 columns imagining raster as a matrix. This decides spatial resolution of raster.

Georeferenced units: Suppose if you set Vertical/Height resolution and  Horizontal/Width resolution as 5 then spatial resolution of each pixel will be 5*5(meaning height and width is 5) and it decides rows and columns of raster matrix.

Output extent: border of raster.

So, that’s all for today we will meet soon in next article.

References:

https://gis.stackexchange.com/questions/379889/qgis-3-16-rasterize-vector-to-raster-parameters

Pirotti, P. F. (n.d.). Multi Criteria Analysis ( MCA ) with GIS Find the best land for growing Mangoes in Madagascar using MCA !

https://www.qgistutorials.com/en/docs/3/multi_criteria_overlay.html

How to log data in Madoca?

What is Madoca?

Madoca is a low cost GNSS receiver that uses QZSS signals to locate position. The whole instrument  consists of a dome shaped antenna, a receiver, a cable connecting antenna and receiver and a USB cable connecting laptop and receiver. Data is collected by precise point positioning method. The errors are automatically corrected by CORS stations and error free data is received by the receiver.

The best thing about Madoca is it is smaller in size, quite cheaper than survey grade receivers and give cm level of accuracy.

Logging data in Madoca

For logging data with Madoca receiver we need to have a desktop application called ‘Madoca Win’ installed on your laptop.

First of all open the ‘Madoca Win’  application. Once the application is opened there are some settings that  are to be adjusted. By default Rover is set to Online, Correction to Online and Processing mode to PPP-Kinematic. Configure  Rover as RX, Correction as DX and Processing mode as PPP-static in the application like shown below.

Fig1:  showing connection setup in MADOCA

Remember if the cables to the antenna or laptop is not connected properly or you don’t have them you won’t see the green loading symbol and values below ROVER, MADOCA and NMEA.

Now we will configure Setup for Rover and Correction

Rover setting
Click on Setup present on the right side of  Rover section. Keep Port and Baud rate value as  COM7 and 115200 respectively. Keep output data in .ubx format which will be later processed in RTKLIB.

Fig2: showing Rover setup setting of MADOCA

Correction settings

Click on Setup present on the right side of  Correction section. Keep Port and Baud rate value as  COM6 and 57600 respectively. Similarly, keep output data in .ubxformat.

Fig 3: showing Correction setup setting of MADOCA

Once all parameters are set data collection is started by clicking start/stop button. 

On successful parameter settingsyou will see the status screen like this.

Fig 4: showing status interface during data collection

You can wait for 30mins or more to log data. Lat/Lon Error goes on decreasing as more log time increases and more error free data can be obtained. You may also need to keep antenna on a tripod as it has better chances of getting QZSS signals quickly specially in crowded areas.

After Lat/Lon error are reduced significantly data log is stopped. Before stopping data log take screenshot of status menu and note down Latitude and Longitude. All logged data are stored in a folder MadocaLog in drive C. Inside MadocaLog folder you will see three folders ‘Correction’, ‘NMEA’ and ‘Rover’ and respective data inside them.

Further you can visualize collected Rover data in ‘RTKLIB’.