Jorge Gustavo Rocha via Qgis-user <qgis-user@lists.osgeo.org> writes:
> I need you help to understand how scale works with geographic > coordinate systems. A good question. > This is my use case: It seems like your minimal example to show what doesn't work like you think it should, instead of what you want to do, but that's good - simpler is better for discussing. > I've draw a polygon with 1000m width and height, and another with > 1500, width and height, sharing the upper left corner. Presumably you have some project CRS, and a layer in which you drew the polygon and it has a layer CRS. You then say width and height, which is a map concept more than an on-the-ground concept. But I'll assume you are using UTM or similar and have a square in UTM coordinates. Presumably also the 1000m is measured in your layer or project CRS. > 1) Using a projected CRS, if I create a layout with a 150mm x 150mm > map, the 1500m polygon fits perfectly on the print area, setting a > 1:10000 scale. That's what I expected. The results is > https://nextcloud.geomaster.pt/index.php/s/TKpkBaqty8BdLL8 That makes sense. > 2) Using a geographic CRS, the same 150mm x 150mm map, at the same > 1:10000 scale, the area is bigger then the 1500m polygon. The result > is attached https://nextcloud.geomaster.pt/index.php/s/H2eAytsPANyxn6Y > > On both layouts the scale bar widget is working properly. The > distances (and areas) are properly calculated in QGIS interface. I > have set the GRS 1980 ellipsoid for distance and area calculations. What does it mean to use a geographic CRS for a print layout? Do you really expect longitude on the x axis and latitude on the y axis? The value of meters/degree is different for x and y, unless you are at or near the equator. (Living at 42N-ish, I'm very aware of this.) > My question is: why the second layout does not fit the 1500m polygon > properly? The second layout shows approximately a 2000m square, > instead of a 1500m square. I would expect Scale to relate units in the project CRS to dimensions on the layout. But, there's perhaps some implicit conversion to meters from geographic coordinates. I wonder if that's happening, and if so if it's a bug -- it feels like a bug to me. I also wonder if geographic coordinates somehow use different scaling on each axis to make it seem more conformal than it is. Overall, it feels like a bug to use geographic coordinates in a print layout. _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user