1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
|
#include <mbgl/geometry/dem_data.hpp>
#include <mbgl/math/clamp.hpp>
namespace mbgl {
DEMData::DEMData(const PremultipliedImage& _image, Tileset::DEMEncoding encoding):
dim(_image.size.height),
border(std::max<int32_t>(std::ceil(_image.size.height / 2), 1)),
stride(dim + 2 * border),
image({ static_cast<uint32_t>(stride), static_cast<uint32_t>(stride) }) {
if (_image.size.height != _image.size.width){
throw std::runtime_error("raster-dem tiles must be square.");
}
auto decodeMapbox = [] (const uint8_t r, const uint8_t g, const uint8_t b){
// https://www.mapbox.com/help/access-elevation-data/#mapbox-terrain-rgb
return (r * 256 * 256 + g * 256 + b)/10 - 10000;
};
auto decodeTerrarium = [] (const uint8_t r, const uint8_t g, const uint8_t b){
// https://aws.amazon.com/public-datasets/terrain/
return ((r * 256 + g + b / 256) - 32768);
};
auto decodeRGB = encoding == Tileset::DEMEncoding::Terrarium ? decodeTerrarium : decodeMapbox;
std::memset(image.data.get(), 0, image.bytes());
for (int32_t y = 0; y < dim; y++) {
for (int32_t x = 0; x < dim; x++) {
const int32_t i = y * dim + x;
const int32_t j = i * 4;
set(x, y, decodeRGB(_image.data[j], _image.data[j+1], _image.data[j+2]));
}
}
// in order to avoid flashing seams between tiles, here we are initially populating a 1px border of
// pixels around the image with the data of the nearest pixel from the image. this data is eventually
// replaced when the tile's neighboring tiles are loaded and the accurate data can be backfilled using
// DEMData#backfillBorder
for (int32_t x = 0; x < dim; x++) {
// left vertical border
set(-1, x, get(0, x));
// right vertical border
set(dim, x, get(dim - 1, x));
//left horizontal border
set(x, -1, get(x, 0));
// right horizontal border
set(x, dim, get(x, dim - 1));
}
// corners
set(-1, -1, get(0, 0));
set(dim, -1, get(dim - 1, 0));
set( -1, dim, get(0, dim - 1));
set(dim, dim, get(dim - 1, dim - 1));
}
// This function takes the DEMData from a neighboring tile and backfills the edge/corner
// data in order to create a one pixel "buffer" of image data around the tile. This is
// necessary because the hillshade formula calculates the dx/dz, dy/dz derivatives at each
// pixel of the tile by querying the 8 surrounding pixels, and if we don't have the pixel
// buffer we get seams at tile boundaries.
void DEMData::backfillBorder(const DEMData& borderTileData, int8_t dx, int8_t dy) {
auto& o = borderTileData;
// Tiles from the same source should always be of the same dimensions.
assert(dim == o.dim);
// We determine the pixel range to backfill based which corner/edge `borderTileData`
// represents. For example, dx = -1, dy = -1 represents the upper left corner of the
// base tile, so we only need to backfill one pixel at coordinates (-1, -1) of the tile
// image.
int32_t _xMin = dx * dim;
int32_t _xMax = dx * dim + dim;
int32_t _yMin = dy * dim;
int32_t _yMax = dy * dim + dim;
if (dx == -1) _xMin = _xMax - 1;
else if (dx == 1) _xMax = _xMin + 1;
if (dy == -1) _yMin = _yMax - 1;
else if (dy == 1) _yMax = _yMin + 1;
int32_t xMin = util::clamp(_xMin, -border, dim + border);
int32_t xMax = util::clamp(_xMax, -border, dim + border);
int32_t yMin = util::clamp(_yMin, -border, dim + border);
int32_t yMax = util::clamp(_yMax, -border, dim + border);
int32_t ox = -dx * dim;
int32_t oy = -dy * dim;
for (int32_t y = yMin; y < yMax; y++) {
for (int32_t x = xMin; x < xMax; x++) {
set(x, y, o.get(x + ox, y + oy));
}
}
}
} // namespace mbgl
|
