# Grid-Based Elevation Tiles

Tacview supports grid-based elevation tiles in `.hgt` or `.Bathymetry.srtm` format which are placed in the appropriate subfolder of

`%PROGRAMDATA%\Tacview\Data\Terrain\` or

`%APPDATA%\Tacview\Data\Terrain\`

The SRTM naming convention is used, where the file name begins with the latitude and longitude of the tile’s lower-left corner (for example `S09E114.hgt` or `e020n90.Bathymetry.srtm`).

### ETOPO1 & SRTM

Tacview displays the worldwise ETOPO1 basemap for users of Tacview Standard and above, and natively supports SRTM1, SRTM3, and SRTM30 files while automatically filling invalid data (holes) using ETOPO1 data. All you have to do is to download the tiles of your choice, unpack the `.zip` archives and install the resulting files in the appropriate folder:

* National Geophysical Data Center [ETOPO1](https://www.ngdc.noaa.gov/mgg/global/global.html) worldwide base map (about 1.25 km resolution)
  * In Tacview, the ETOPO1 worldwide basemap is displayed for users of Tacview Standard and above.
* Shuttle Radar Topography Mission [SRTM30](https://topex.ucsd.edu/pub/srtm30_plus/srtm30/data/) (about 750 m resolution)
  * These `.Bathymetry.srtm` files must be placed in
    * `%PROGRAMDATA%\Tacview\Data\Terrain\SRTM30\` or
    * `%APPDATA%\Tacview\Data\Terrain\SRTM30\`
* Shuttle Radar Topography Mission [SRTM3](http://www.viewfinderpanoramas.org/Coverage%20map%20viewfinderpanoramas_org3.htm) (about 75 m resolution)
  * These `.hgt` files must be placed in
    * `%PROGRAMDATA%\Tacview\Data\Terrain\SRTM3\` or
    * `%APPDATA%\Tacview\Data\Terrain\SRTM3\`
* Shuttle Radar Topography Mission [SRTM1](https://search.earthdata.nasa.gov/search?q=SRTMGL1%20V003) (about 25 m resolution)
  * These `.hgt` files must be placed in
    * `%PROGRAMDATA%\Tacview\Data\Terrain\SRTM1\` or
    * `%APPDATA%\Tacview\Data\Terrain\SRTM1\`

After downloading tiles from these sources, re-launch Tacview and go to `Options`→`Terrain` to ensure that `Real Terrain` is enabled.

![Terrain Elevation Menu Option](/files/tSL0QeBgJTJLb7zIPbyE)

### Dealing with SRTM tiles which have holes

Because of the radar technique used during [Shuttle Radar Topography Mission](https://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Mission), canyons and mountains can contain quite a lot of holes. Tacview is doing its best by filling holes using the available low-resolution [ETOPO1](http://www.ngdc.noaa.gov/mgg/global/global.html) data. However this does not always give perfect results. This is why, you may want in some cases, to download pre-filtered data or to use a dedicated program to filter terrain data in a smarter way.

The first thing to do is to look for pre-filtered data on [Jonathan de Ferranti's web site](http://www.viewfinderpanoramas.org/Coverage%20map%20viewfinderpanoramas_org3.htm). These data are cleaned-up using topographic data coming from several alternate sources and usually gives great results.

If you can't find any pre-filtered data or you are not happy with the ones provided, you may want to try a filtering program such as Blackart. (<https://ln5.sync.com/dl/eb1858a80#tawsdmhs-4qjc4rdi-59ajsu8i-jasdnekg>).

* Select `File | Batch Mode Interpolate | SRTM to SRTM`
* Add your `SRTM` files to the list
* Press `[Continue]`
* Set `LSQR Iterations` to `100`
* Set `Laplacian Iterations` to `1000`
* Reset the `Scale Factor` to `1` (because the decimal separator may not be properly handled)
* Click on `[Submit]`, accept the default `-32000` value for null data then `[Submit]`
* Select `Run | Run Blackart`
* Copy the resulting files in the appropriate Tacview folder and rename them from `.hgx` to `.hgt`

![Terrain Elevation - Blackart](/files/9b9zqV979NgDu7gcaVLW)


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