Maps SDK for Qt display Geotiff with transparent background
I am evaluating the ArcGIS Maps SDK for Qt to see if it fits our needs. To test it, I have done a small project for a map and scene viewer. In both viewers, I import a GeoTIF (data/orofotomosaic.tif in the project) which is an RBGA image. However, the image is shown with with background instead of transparency (in the attached image there's also another GeoTIF displayed in green scale which is not relevant to this post):
The way I create that raster layer is:
Esri::ArcGISRuntime::Raster *raster = new
Esri::ArcGISRuntime::Raster("path/to/photomosaic.tif", parent);
Esri::ArcGISRuntime::RasterLayer *raster_layer = new Esri::ArcGISRuntime::RasterLayer(raster, parent);
How can I keep the transparent background of the imported TIF file?
I just stumpled upon this now as well. I thought one might be able to use a ColormapRenderer as illustrated here: Colormap renderer | ArcGIS Maps SDK for Qt | Esri Developer
However, using transparent colors does not seem to work. Funnily enough, when there are values that have no corresponding color they are rendered transparent! Is this a bug? Seems to me like it is...
In this example I defined 500 colors with the rules
< 250: Transparent. But it is rendered black!
< 300: Yellow.
< 400: Red.
> 400: Dark Red.
As you can see all values above 500 (i.e. more than the number of defined values), are rendered transparent!
Here is the code I used:
void ColormapTest::setup()
{
// [...]
Raster* raster = new Raster(filepath, this);
m_rasterLayer = new RasterLayer(raster, this);
ColormapRenderer* colormapRenderer = createColormapRenderer(m_rasterLayer);
m_rasterLayer->setRenderer(colormapRenderer);
m_map->operationalLayers()->append(m_rasterLayer);
}
ColormapRenderer*
ColormapTest::createColormapRenderer(QObject* parent)
{
QList<QColor> colors;
int maxValue = 500;
colors.reserve(maxValue);
for (int i = 0; i < maxValue; ++i) {
if (i < 250) {
colors.append(Qt::transparent);
} else if (i < 300) {
colors.append(Qt::yellow);
} else if (i < 400) {
colors.append(Qt::red);
} else {
colors.append(Qt::darkRed);
}
}
ColormapRenderer* colormapRenderer = new ColormapRenderer(colors, parent);
return colormapRenderer;
}
I don't understand how the ColormapRenderer is supposed to work ColormapRenderer Class | ArcGIS Maps SDK for Qt | Esri Developer
In the ctor one can only pass QList<QColor>. How can we define colors for negative values? Do we have to apply a raster function to normalize the values between 0 - 255 beforehand? If we rearrange the values so that everything above a certain value has no color defined, then we can render them fully transparent... Sadly no opacity is supported this way.
