# QGIS use sheetlines for atlas automatic map extent

I have sheetline geometries for the German TK50 1:50.000 map extents. I now want to create an atlas for the geometries. So far no problem, I have this working.

But the sheetline geometries cover 40' long and 24' lat, which always results in the height of 22.2 km but varying widths between 25.2 and 21.2 km. I know I can programmatically adjust the size of the drawn map but therefore I need to figure out the width. The geometries come projected EPSG:25832 (ETRS89 / UTM zone 32N). This makes them turned and that results in bounds_width not getting the right width of the sheetline widthwise.

Can anyone point me in the right direction? I mean I can't be the first one trying to recreate a map by a given sheetline.

• Values in degrees are correctly rendered in different lengths depending on latitude. Are you sure you aren't trying to create a problem? Jan 27 at 21:38
• I want the map as a WGS84 UTM projection. This will make the single sheetline map extent vary in width. That's what I need to adjust for. You made me think of if there was a function to get a length from the degree lat value, but I can't think of one right now Jan 27 at 22:37
• ETRS89 UTM isn't the same as WGS84 UTM, so you need to do datum transformation, too. There a number of implementations of a function to calculate geodesic length in degrees, but it's a partial differential equation that can only be solved by iterative means, so it's not likely to be recalled. Jan 27 at 22:55
• Your comment gave me the intent to research more. I now get more to the source of the problem. A Pseudo-Mercator projection gives me sheetline geometries all straight, but of course not distance conserved. A UTM-Projection conserves distances but makes my sheetline-geometries tilted, I need to adjust for convergence. But being tilted I can't calculate the sheetlines width for the map extent plus I found no QGIS only way for calculating convergence. What am I overseeing? I want to create a map like link Jan 29 at 11:43