Problem concerning Scales/Resolutions and Tiled Services

pgs...@gmail.com

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Mar 8, 2021, 9:32:58 AM3/8/21

to mapstore-users

Hi all,

I have the following customised gridSet in Geoserver (using GeowebCache with Direct integration with GeoServer WMS)

So, I’ve customised the resolutions in mapstore to match geoserver scales, as you can see below:

{

"version": 2,

"map": {

"projection": "EPSG:25830",

"units": "m",

"center": {"x": 636000, "y": 4200000, "crs": "EPSG:25830"},

"zoom":6,

"maxExtent": [

227071.8572857892, 3901876.695336829,

772928.1427142108, 8942165.537905218

],

"mapOptions": {

"view": {

"resolutions": [

2187.6253656980857,

1093.8126828490429,

546.9063414245214,

273.4531707122607,

136.72658535613036,

68.36329267806518,

34.18164633903259,

17.090823169516295,

8.545411584758147,

4.272705792379074

]

}

},

"layers": [

……

However, you can see at following screenshot from a new map in mapstore missmatching scales with geoserver. This missmatching I think leads to problems due to the client making WMS requests (mapstore) that do not align with the grid of tiles that GeoWebCache has created.

I would be very grateful if anyone can help me with this problem or clarify me how it works.

Thanks a lot.

Petar Sapunar

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Mar 8, 2021, 9:42:55 AM3/8/21

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Hello pgs93h

as i recall, several people had the same problem. In essence the problem with "new.json" is that you are defining resolutions and not scales. i think you can just go something like this:

"scales": [

1:100,

1:200,

1:3000,

etc. search the github forum and mapstore groups i think you will find the answer.

https://groups.google.com/g/mapstore-users/c/J418lCt4mtQ/m/3_6CusdZCAAJ

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pgs...@gmail.com

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Mar 9, 2021, 6:39:09 AM3/9/21

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Sorry but I think I don't understand you. Your proposal about "scales" doesn't work (I've replaced 'resolutions' by 'scales' and filled with related scales ).

Besides, I've read your link and applied what Mauro Bartolomeoli says about

- scale = resolution * dpu where dpu = dpi * (100 / 2.54), where dpi = 96

and although at small scales (zoom out) works fine, but a bigger scales (zoom in, more details) appears again problems related to grid misalignment, as it showed in the following message:

400: Requested horizontal resolution: 2145.5411359375003 , best match: 2445.984905625 exceeds 10% threshold. Perhaps the client is configured with an incorrect set of scales (resolutions), or the DPI setting is off compared to the one in GWC ?

So, that makes me believe that mapstore uses different method to calculate scales versus geoserver. Any idea?

Regards.

Stefano Bovio

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Mar 15, 2021, 6:47:54 AM3/15/21

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Hi psg93h,

Sorry but I think I don't understand you. Your proposal about "scales" doesn't work (I've replaced 'resolutions' by 'scales' and filled with related scales ).

Scales property did not work before but it was recently added to MapStore master branch and it uses a list of scales denominators
https://github.com/geosolutions-it/MapStore2/pull/6577

Besides, I've read your link and applied what Mauro Bartolomeoli says about
- scale = resolution * dpu where dpu = dpi * (100 / 2.54), where dpi = 96

The scale box tools shows only the list of scales and it has not effect on the request and the missmatch seems due to different DPI used as you noted. https://github.com/geosolutions-it/MapStore2/blob/master/web/client/utils/MapUtils.js#L206
The gridset in GeoServer seems to use a DPI of ~90.7 and we are using it in the WMTS request to get the correct scales see here:
https://github.com/geosolutions-it/MapStore2/blob/master/web/client/components/map/openlayers/plugins/WMTSLayer.js#L57-L62

and although at small scales (zoom out) works fine, but a bigger scales (zoom in, more details) appears again problems related to grid misalignment, as it showed in the following message:
400: Requested horizontal resolution: 2145.5411359375003 , best match: 2445.984905625 exceeds 10% threshold. Perhaps the client is configured with an incorrect set of scales (resolutions), or the DPI setting is off compared to the one in GWC ?

I tried also to test that gridset locally and I did not find artifacts or misalignements on the different zoom levels,

these are the steps I followed:
- configured a new gridset EPSG:25830 on geoserver and assigned this new gridset to a layer

- add to localConfig the new projection in the projectionDefs property https://mapstore.readthedocs.io/en/latest/developer-guide/local-config/#projectiondefs-configuration
"projectionDefs": [{
"code": "EPSG:25830",
"def": "+proj=utm +zone=30 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs",
"extent": [-729785.76, 3715125.82, 945351.10, 9522561.39],
"worldExtent": [-16.1, 32.88, 40.18, 84.17]
}
- copied your new json configuration in a static map
- imported the layer in the map

wmts (cropped on the tile extents of gridset)

wms

tried also to zoom in but there were not visible artifact or misalignement on the tiles.

Hope this information could help,
Regards,

Stefano

To view this discussion on the web visit https://groups.google.com/d/msgid/mapstore-users/5ba8f462-79bf-4cd9-ab9d-ba59b6e012ffn%40googlegroups.com.

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Regards,

Stefano Bovio

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