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
|
#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),
// extra two pixels per row for border backfilling on either edge
stride(dim + 2),
encoding(_encoding),
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* dest = reinterpret_cast<uint32_t*>(image.data.get()) + stride + 1;
auto* source = reinterpret_cast<uint32_t*>(_image.data.get());
for (int32_t y = 0; y < dim; y++) {
memcpy(dest, source, dim * 4);
dest += stride;
source += dim;
}
// 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
auto* data = reinterpret_cast<uint32_t*>(image.data.get());
for (int32_t x = 0; x < dim; x++) {
auto rowOffset = stride * (x + 1);
// left vertical border
data[rowOffset] = data[rowOffset + 1];
// right vertical border
data[rowOffset + dim + 1] = data[rowOffset + dim];
}
// top horizontal border with corners
memcpy(data, data + stride, stride * 4);
// bottom horizontal border with corners
memcpy(data + (dim + 1) * stride, data + dim * stride, stride * 4);
}
// 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 ox = -dx * dim;
int32_t oy = -dy * dim;
auto* dest = reinterpret_cast<uint32_t*>(image.data.get());
auto* source = reinterpret_cast<uint32_t*>(o.image.data.get());
for (int32_t y = yMin; y < yMax; y++) {
for (int32_t x = xMin; x < xMax; x++) {
dest[idx(x, y)] = source[idx(x + ox, y + oy)];
}
}
}
int32_t DEMData::get(const int32_t x, const int32_t y) const {
const auto& unpack = getUnpackVector();
const uint8_t* value = image.data.get() + idx(x, y) * 4;
return value[0] * unpack[0] + value[1] * unpack[1] + value[2] * unpack[2] - unpack[3];
}
const std::array<float, 4>& DEMData::getUnpackVector() const {
// https://www.mapbox.com/help/access-elevation-data/#mapbox-terrain-rgb
static const std::array<float, 4> unpackMapbox = {{ 6553.6, 25.6, 0.1, 10000.0 }};
// https://aws.amazon.com/public-datasets/terrain/
static const std::array<float, 4> unpackTerrarium = {{ 256.0, 1.0, 1.0 / 256.0, 32768.0 }};
return encoding == Tileset::DEMEncoding::Terrarium ? unpackTerrarium : unpackMapbox;
}
} // namespace mbgl
|
