Projections in GIS

[@HansvanderKwast]

A useful site when you're stuck with projections: ihatecoordinatesystems.com

[@toonverberg1313]

Thanks for taking away my blindfold in this QGIS-labyrinth. Now I can focus again on getting along with my research. 💪

[@lucabellani3442]

I love your job Dr. Hans. Muchas gracias!

[@robinkohrs8097]

thank you very much!!:) Should have known this since years... Now I got it;)

[@hotnewsgossips7923]

Thanks you Sir for the awesome lecture. My case is quite different. I am modelling Eco-Hydrology of a very large river basin. The river cuts across several UTM zones (28, 29, 30, 31, 32 and 33). How can I handle the projection of the SRTM DEM on this large river basin? Please I really need need your expertise and advise on DEM analysis here. The project is for my PhD thesis. Thanks and God Bless.

[@HansvanderKwast]

You can choose one UTM zone and use it across the study area or you choose another projection, such as the pseudo mercator (EPSG: 3857). Also note that for such large areas you'll get stuck if your spatial resolution is too high. Your calculations will take too long or your computer will crash. Instead of SRTM 1 Arc Second you might want to use 3 Arc Second or even coarser.

[@hotnewsgossips7923]

My River Basin is the Niger River Basin, West Africa, and crosses 9 countries in Africa. Thank you sir.

[@hotnewsgossips7923]

Thanks you Sir for the awesome lecture. My case is quite different. I am modelling Eco-Hydrology of a very large river basin. The river cuts across several UTM zones (28 N, 29 N, 30 N, 31 N, 32 N and 33 N). How can I handle the projection of the SRTM DEM on this large river basin? Please I really need need your expertise and advise on DEM analysis here. The project is for my PhD thesis. Sorry for the initial mistake on the UTM

[@HansvanderKwast]

Choose the UTM zone of the largest area or use another projection that is valid over larger areas.

[@Ian-zx1cc]

Hi Sir, Thanks for the Video. I was preparing a DEM for Hydrological Analysis. I want transform it from [EPSG:4326] to a projection that suits Kenya best which is [EPSG:4210 Arc 1960], however, when i try to set the 'Target CRS' as [ EPSG:4210 Arc 1960] i get an error. When i use Target CRS [EPSG:21096 'Arc 1960 / UTM zone 36N'] the reprojection seems flawless and works. I believe i must have missed some fundamentals of this topic, is there a reason for this?

[@HansvanderKwast]

For DEM analysis you need to use a projected CRS. You can't use a Geographic Coordinate System (GCS) with units lat/lon degrees. This is the case with EPSG 4326 and 4210 for example. More info on this in the videos on DEM analysis and stream and catchment delineation.

[@hotnewsgossips7923]

Thanks you Sir for the awesome lecture. My case is quite different. I am modelling Eco-Hydrology of a very large river basin. The river cuts across several UTM zones (28, 29, 30, 31, 32 and 33). How can I handle the projection of the SRTM DEM on this large river basin? Please I really need need your expertise and advise on DEM analysis here. The project is for my PhD thesis. Thanks and God Bless.

[@lucabellani3442]

Good day. I have a doub: when you show the option with 2 layer with your own EPSG, and the project in a third system, which system does QGIS use for the geometric calculations? the one about the project? thank you!

[@HansvanderKwast]

Hi Luca. It will use the projection of the layer if you use fuctions like $x, $y, $length, $area in the attribute table. Same for processing tools. If you use geometry generator and tools to measure in the map canvas it will use the OTF reprojection coordinate system.

[@lucabellani3442]

@@HansvanderKwast , Thank you very much, I did not know these details !!

[@sureshpatil1817]

Hello sir I have one doubt. I am calculating length and area by using wgs 84 EPSG 4326. If i have to calculate slope (From DEM), then can set the same setting or i have to set some another setting such as wgs 84 EPSG4326 or UTM 43N(Which is for my area)

[@HansvanderKwast]

For DEM analysis, like calculating slope, it is always better to reproject your DEM. x and y units in EPSG:4326 are in degrees, while z is in meters. The slope tool will work but results will be wrong. Therefore you have to reproject to UTM or other metrical CRS. See also: kzbin.info/www/bejne/kH24m4Z7gJKhmMk the part about reprojection.

[@sureshpatil1817]

@@HansvanderKwast thank you sir