Help with drawing contours and determining quotas - hypsometry

[Marcusiuss]

Hello, I would like to ask you - the experts - for help with one homework assignment for credit. We have a total of three attempts to submit one map. I missed one attempt due to my social situation and the absence of a laptop. Of course, I have a library at my disposal, but it's only open half a day and I can't borrow a laptop because - as I'm sure you understand - I don't want to walk down the street and into the forest - someone might steal it. I can't be in the dormitory at the moment because of full capacities and hostels and other accommodation facilities are full. I prefer to wait for free capacity - since the dormitories are cheap and the cheapest hostel will cost me five times the price of one night in the dorm. Yes, you heard me right, I sleep in the forest because of the large number of thefts in Prague, and in the forest, in such a dwelling, no one can rob me. /kol reads as follows: I missed the first attempt and fellows who practice with me, about 97% of people had an unrecognized bad map and received zero points instead of the full -15 points. I didn't hand in any map on the first attempt - it is possible to draw it by hand, but the trainer - a woman - said that it was very risky due to errors and inaccuracies. So we got some random program - it's called OO Mapper, where we have to draw the map. There are other programs where it is possible to draw, like CAD or ARCGis - which I have installed and I will try to do it in it. I have to submit the map to the mailbox by 12:00 tomorrow - now it is already -10 for the full number of points, it decreases with each attempt, and on the third attempt it is only 5 points full. I am asking you - experts - on the CAD forum and everywhere else, if there is an opportunity to explain to me the solution to the example of drawing contours with elevations and a flowing river, including the supplementary contour and the slope contour and the elevation - the number that is located in the contour and not marked with a cross. I've been given this map - on which I'm supposed to use a grid - which will be offset about 1cm from the edge.

1. At all intersections, I have to find the height above sea level with an accuracy of one meter - please, how should I find the height above sea level, when I don't know how, and it is only stated there that if there is no other way, the height can be found based on the distance of d from the nearest contours. Then I should transfer this grid and the intersections - dimensions - to a new A4 sheet, where I will mark the contour lines - by linear interpolation

1. On the grid, I should mark the intersections of the line segments with contour lines - dashed and connect the intersections to create contour lines. Please, I have read countless documents and books where this is not explained. I only found this method, which I described and then the method of triangulation - like some girls in the subway at O2 in the ads - where there are similar triangles - triangulation and the contour is supposed to flow through them. Honestly, does it have to be calculated according to the formula, where should the contour go, or can it be done by eye? Another method is the Voroné diagram - where it is the English Natural Neighboiur - or Thiessen's polygomes, where it is solved geometrically. Can you please advise me how to draw it quickly or in another way?

3. I should mark the flowing river there, including the additional contour, then the numbers that are marked directly into the contour and the gradient.
Can I ask you - experts - for advice and at least how should I proceed when creating quotas, painting contours and whether it is better to do it manually or how to proceed when creating in the application? Is it not possible to somehow download the area from the internet, just a contour line on a white background with a flowing river, altitude quotas in the form of 2 connected triangles and an additional contour line?

I am attaching a sample map of how it should look. In addition, I was given a map of the Moravian-Silesian region, and now I don't know if I should somehow scan the map into the program and get the required information from there, or should I find the area in the program? In addition, it would not be possible to work it out manually from a printed map - input?

I am attaching a hypsometry map of how it should look like and my assignment of a map of the Moravian-Silesian region

Thanks for any advice

[Redrobes]

I can help with some of this but not sure all of it. But I think I understand the contour question. Taking your middle image it has a point with a cross of 308m and you can see that its close to a contour line. That line is 310m. Counting up contour lines we can count 5 of them and see that there is a cross not too far from the 360m contour line marked 357m.

So we know that the contour lines are marked in 10m intervals.

A linear interpolation makes the assumption that between the contour lines it is a straight line. Now we know thats an approximation but its going to be pretty close. So now you can take any point on the map and find the contour line above it and below it and then those are the 10m intervals either side of your point. You take a straight line and draw it across the contour lines such that its as close as possible to being perpendicular to them that passes through your point. Now between your point you have a distance dhigh which goes from your point to the contour line above and a dlow which is the distance from that point to the lower contour line.

We know that dlow + dhigh is 10m. So dlow / (dlow + dhigh ) * 10m is the height offset from the lower of the contour lines. That is the linear interpolation of the point between the two reference values.

So if the lower contour line was 310m and you had dlow as 8mm and dhigh as 12mm then you have 8 / (8+12) * 10 is 80/20 = 4m of height to offset so the final height above sea level is 314m.

You can do that for any point on the map whether intersections of roads or whatever. Just so long as you have the contour lines either side of it.

Voronoi is the 2D version of that linear interpolation. Its a bit more tricky but it requires having 3 points instead of two. So if you know the heights of three points around the one your trying to figure out - even if you dont have contour lines now - then you can linear interpolate them making the assumption that the ground is linear and flat at some angle of steepness. This is obviously an approximation so the closer those known points are around the one you don't know the better.

To do the Voronoi interpolation you just do a two point interpolation across any of the two out of the three known ones and then now that you have that edge line you can draw a line through your unknown point to the third known one. Where that line will cut / bisect the first line you need to find that bisection height first using the same technique as above for the contours. Then linearly interpolate that to the third point and that gives you your unknown one.

A
*....
 .    ....
  .       ....
   .          ...
   P.---U-------*B
     .        ..
      .     ..
       .  ..
        ..
         *C

So draw a line through U to B creating a point P. Linearly interpolate line A to C and find height at point P. Then linearly interpolate from P to B at your unknown point U to find its height.

Hope this helps and maybe we might get a few more suggestions.

[Tiana]

I missed the first attempt and fellows who practice with me, about 97% of people had an unrecognized bad map and received zero points instead of the full -15 points.

I've never been in academia but that sounds like a badly worded assignment that is either missing information relevant to complete it or not given enough time, and I would definitely bring it up to the teacher and if they are not receptive to feedback, whoever is above them.

Because I mean, if even the professionals are like "I need more information and time to complete this" I don't know how students are supposed to. 97% of students failing to hand in a map sounds like a very badly set up assignment.

This is what I'd do to get contours. https://opengislab.com/blog/2022/2/2...dem-using-qgis

Using these, I was able to extract these contours. I got the OpenTopoMap basemap and terrain measurements on the contours. Didn't get the rivers in with this tutorial, but the contours from the NASA DEM data will probably work?



On this one I did 10 meter contours (I think) and added the water using QuickOSM.