standalone: add --viewer-height to add observer height above DEM ground

[thannart]

Lets you account for the fact that the viewer isn't standing at ground level (e.g. an apartment floor), by reusing horizonator_move() to reposition the camera at ground_elevation + viewer_height after the usual auto-selected ground elevation is computed.

[dkogan]

Hi. Thanks for the patch. If we're going to do this, I'd like to do a little bit better. Instead of an extra call to horizonator_move(), can we update the APIs for horizonator_move() and horizonator_init(), to allow this the height to be given in respect to the DEM instead of in absolute terms? Currently we have:

bool horizonator_init( // output
                       horizonator_context_t* ctx,

                       // input
                       float viewer_lat, float viewer_lon,
                       // output/input
                       // if viewer_z==NULL, auto-select a value; if *viewer_z >=
                       // 0, use that; if *viewer_z < 0, auto-select a value, and
                       // report it here
                       float* viewer_z,
                       int offscreen_width, int offscreen_height,
                       int render_radius_cells, // This should be given >0
                       float render_radius_m,   // or this, but not both

                       bool use_glut,
                       bool render_texture,
                       bool SRTM1,
                       const char* dir_dems,
                       const char* dir_tiles,
                       const char* tiles_name,
                       const char* tiles_url_fmt,
                       bool allow_downloads);
bool horizonator_move(horizonator_context_t* ctx,
                      // output/input
                      // if viewer_z==NULL, auto-select a value; if *viewer_z >=
                      // 0, use that; if *viewer_z < 0, auto-select a value, and
                      // report it here
                      float* viewer_z,
                      // input
                      float viewer_lat, float viewer_lon);

Among other things, this API breaks below sea level. Can you update the code to use this API instead?

bool horizonator_init( // output
                       horizonator_context_t* ctx,
                       // if non-NULL, report the elevation of the DEM here
                       float* viewer_z_dem,

                       // input
                       float viewer_lat, float viewer_lon,
                       float viewer_z, // either above sea level, or above the
                                       // DEM, depending on the next argument
                       bool viewer_z_is_given_above_dem,
                       int offscreen_width, int offscreen_height,
                       int render_radius_cells, // This should be given >0
                       float render_radius_m,   // or this, but not both

                       bool use_glut,
                       bool render_texture,
                       bool SRTM1,
                       const char* dir_dems,
                       const char* dir_tiles,
                       const char* tiles_name,
                       const char* tiles_url_fmt,
                       bool allow_downloads);
bool horizonator_move(// output
                      horizonator_context_t* ctx,
                      // if non-NULL, report the elevation of the DEM here
                      float* viewer_z_dem,
                      // input
                      float viewer_lat, float viewer_lon,
                      float viewer_z, // either above sea level, or above the
                                      // DEM, depending on the next argument
                      bool viewer_z_is_given_above_dem);

Seems reasonable? Then the default usages would pass viewer_z=0, viewer_z_is_give_above_dem=true. And YOU could pass larger viewer_z.

And if you make frontend changes, can you please modify the standalone.c and horizonator.cc? Let me know if that sounds reasonable. Thanks

[dkogan]

Can you also update the python API to use this interface update? horizonator-pywrap.c and the two .docstring files. Let me know if that makes sense. Thanks