Resolution & Dimensions Vs. Scale

RESOLUTION

The Resolution of your DTM data is the distance between the height points. If you’re using GeoTiff format, this is essentially the size of each pixel. It has a direct impact on the level of detail of your landscape.

Worldwide DTM data is available from a number of sources (SRTM, ASTER, etc.) at 1 arc-second (approximately 30m/pixel). This is the lowest resolution data you will want to use in UE4 – it means a height measurement is taken every 30m, so it’s not very detailed (most of the lumps and bumps you want to make the landscape look realistic aren’t there).

Ideally you’ll find data of 1m to 5m/pixel resolution, which is detailed enough to make your landscape look realistic. Higher than this (<1m/pixel) and you're not really getting more value. Remember that DTM data is normally collected using satellites or aircraft with sensors that detect the altitude of the first thing the sound or laser hits (trees, buildings etc.). DTM data has to be edited to remove these 'first surface returns', so it's always interpreted. Super high resolution DTMs will include lots of measurements for tiny stuff on the ground, which makes it increasingly difficult for software to remove so that you end up with the actual height of the terrain.

DIMENSIONS VS. SCALE

UE4 landscapes are made up of Quads, Components and Sections. There’s a really good guide to landscapes from Epic here.

In short, quads are the smallest unit of a landscape (you can think of them like the area between 4 pixels. Quads are grouped into Sections in powers of 2 (Quads per Section). Sections are grouped into Components – either 1 Section per Component, or 4 Sections per Component (2×2). You can increase the number of Components X and Y to give you the Overall Resolution of your landscape. These settings affect performance, so if you’re planning something really detailed or large, it might be worth giving the above article a read.

Epic recommends a maximum Overall Resolution of 8129 x 8129 (you can go larger, but you might have issues with performance). The size of your landscape will be the overall resolution multiplied by the pixel size (e.g. if you’re using 8129×8129 with a 1m/pixel resolution, your terrain will be 8.129km x 8.129km.

To create landscapes larger than 8.129km x 8.129km in a landscape, you can decrease the resolution of the DTM data (if you use 5m/pixel, your landscape will be 40.645km x 40.645km). We’ve imported data at 30m/pixel to create a single landscape 240km x 240km, but we wouldn’t necessarily recommend this since UE4 uses single float precision, meaning errors can creep in at large distances from the origin.

IMPORTANT

UE4’s landscape collision mesh requires that a landscape’s x and y scale values are the same. TerraForm will allow you to create landscapes with different x and y scale values, but this can cause issues with detecting the landscape – i.e. in some instances players and objects can fall through.

NON-SQUARE LANDSCAPES

We would recommend you create square landscapes. This is the easiest way to ensure that the x and y scale values of the landscape are the same (see above).

If it’s important for you to create non-square landscapes, we’d highly recommend doing a bit of maths first:

1. Calculate the Overall Resolution of the landscape you want to create first.
2. Clip your DTM data to dimensions of the same ratio as the Overall Resolution.

For example, if the landscape you want to create has an Overall Resolution of 4446×3557 (127 Quads per Section x (1×1 Sections per Component) x (35 Compoenents X and 28 Compoenents Y), you should clip your vector data using the ratio 4446:3557.

(The eagle-eyed mathmaticians among you will notice that the Overall Resolution is 1 greater in X and Y than the maths above suggests. This is because quads have 4 sides and the Overall Resolution refers to the corner points, rather than the area defined in between.)